CN104525913A - Guardrails and a manufacturing method thereof - Google Patents

Abstract

The object of the present invention is to provide a guard rail, the surface of the working part of which has a carbide coating, and to provide a preparation method for obtaining such a guard rail. The guard rail has a carbide coating on the upper and lower surface working parts. The quasi-single crystal WC dense ceramic layer, the micron WC ceramic layer and the composite layer of WC and matrix are distributed sequentially in a gradient from outside to inside, and are applied on the surface of carbon steel. In the present invention, the matrix and the tungsten composite body obtained by casting are introduced with an external carbon source, heated and kept warm, so that a carbide coating is formed on the surface of the matrix. The coating and the matrix are metallurgically bonded, and the bonding force is very strong. It overcomes the problems of non-metallurgical bonding between the existing hard particles and the metal matrix, the bonding force is weak, and the particles are easy to fall off, and the wear resistance of the working surface of the guard rail is greatly improved.

Description

Guard rail and preparation method thereof

technical field

The invention relates to a guard rail with a wear-resistant coating and a preparation method thereof, in particular to a guard rail with a wear-resistant carbide coating and a preparation method thereof, in particular to a wear-resistant carbide applied to the surface of carbon steel Coated composite guard rail and preparation method thereof.

Background technique

The railway guard rail is one of the essential parts at the railway turnout, which is used to ensure the safe and smooth passage of the train when passing the turnout. At present, the guard rails used in railway turnouts are generally made of rail steel. The guard rails made of rail steel are not high in hardness and poor in wear resistance. Under the impact and friction of high-speed wheels, the guard rail working surface (similar to the rail One side) wearing and tearing is faster, and service life is lower, and this has undoubtedly increased the on-site maintenance workload and use cost, and has a strong impact on train driving safety. In recent years, in order to improve the service life of the guard rail, various countries have conducted research on strengthening the guard rail from different aspects. At this stage, it is often used to prepare reinforced coatings on the surface, which can ensure that the wear resistance and other mechanical properties of the surface can be greatly increased on the basis of the original characteristics of the substrate, and the service life of parts such as guard rails can be improved, and the cost can be reduced.

The coating of carbide material is a kind of material that is widely used at this stage. It has the characteristics of high hardness and excellent wear resistance. Covering the surface of the metal alloy substrate by coating can improve the resistance of parts made of the substrate material. Grinding and longevity. Carbide materials have the characteristics of high hardness and excellent wear resistance. Among them, WC is a common coating material, which has the following characteristics:

(1) Tungsten carbide has high strength, high hardness and high modulus;

(2) WC has good toughness, good impact load resistance and wear resistance, and has good interfacial corrosion resistance when combined with the matrix, and it has good wettability with steel, and the wetting angle between the two is zero;

(3) Secondly, my country is a country rich in tungsten, so it is very suitable to choose WC as the reinforcement phase in terms of technical, economic and social benefits.

Therefore, WC coating is widely used as chipless cold and hot metal processing tools, cutting tools, various molds, wear-resistant, heat-resistant and corrosion-resistant parts surfaces, etc.

At present, the surface coating technology of metal materials includes: laser cladding method, high temperature self-propagating sintering technology, powder metallurgy technology, material vapor deposition technology (including: chemical vapor deposition (CVD), physical vapor deposition (PVD)), etc. The method of material coating includes chemical vapor deposition method, physical vapor deposition method, thermal spraying method, hot-dipping method, etc., but these methods have the disadvantages of demanding production equipment, low production efficiency, and low coating bonding strength.

Therefore, how to obtain a WC-phase coating on the working surface of the guard rail, and choose a preparation method with simple production equipment and short process flow, to obtain a coating with good adhesion to the substrate, not easy to fall off, and excellent mechanical properties and wear resistance is a must. Problems to be solved.

Contents of the invention

The object of the present invention is to provide a kind of guard rail, the surface of its guard rail has a kind of wear-resistant coating, and the core of guard rail is still carbon steel substrate, and this wear-resistant carbide coating is WC dense ceramic layer, and its chemical Good stability and wear resistance, low friction coefficient, high hardness, low surface energy and low heat transfer; and further, a preparation method for obtaining the above guard rail is provided.

Further, the present invention also provides a composite guard rail, which has a gradient composite coating on its guard rail surface, and the gradient composite coating is a carbide coating, which is preferably coated on the surface of a metal substrate to improve its surface hardness. wear resistance and fracture toughness, especially on carbon steel or cast iron surfaces, and provides a preparation method for obtaining said coatings.

The guard rail has a wear-resistant coating on its working part. The coating is beneficial to ensure that the working surface of the guard rail has high hardness and good wear resistance, while the inside of the guard rail matrix has good toughness.

For realizing the object of the present invention, the present invention adopts following technical scheme:

A kind of guardrail, the surface has wear-resistant coating, and this wear-resistant coating is WC dense ceramic layer; Preferably, WC dense ceramic layer is quasi-single crystal phase, and described quasi-single crystal phase refers to, between polycrystalline phase Compared with the single crystal phase, the crystal orientation is highly consistent, the grain boundaries are significantly reduced, and the atomic arrangement is relatively orderly.

More preferably, along the longitudinal section of the WC dense ceramic layer, its thickness is 50-180 μm, preferably 100-180 μm; preferably, wherein the volume fraction of WC is greater than 80%, preferably greater than 85%, preferably, its particle size is 10 -50 μm, preferably 20-50 μm.

In addition, the present invention also provides a guard rail with a gradient composite coating on the surface. The gradient composite coating is a carbide coating, including a WC dense ceramic layer, a micron WC ceramic layer, a WC and a matrix that are sequentially distributed in a gradient. fusion layer.

Preferably, the WC dense ceramic layer is a quasi-single crystal phase, which means that it is between a polycrystalline phase and a single crystal phase. Compared with a polycrystalline phase, the crystal orientation is more consistent and the grain boundaries are obvious Reduced, and the atomic arrangement is relatively orderly microstructure.

More preferably, along the longitudinal section of the WC dense ceramic layer, its thickness is 50-180 μm, preferably 100-180 μm; preferably, wherein the volume fraction of WC is greater than 80%, preferably greater than 85%, preferably, its particle size is 10 -50 μm, preferably 20-50 μm.

Further preferably, along the longitudinal section of the micron WC ceramic layer, its thickness is 70-180 μm, preferably 130-180 μm; wherein the volume fraction of WC is greater than 75%, preferably greater than 80%, and its particle size is 5-30 μm, preferably 6 -25 μm.

More preferably, along the longitudinal section of the fusion layer between WC and the matrix, its thickness is 60-300 μm, preferably 100-300 μm; wherein the volume fraction of WC is 40-80%, preferably 60-80%, and its particle size is 1-20 μm, preferably 5-10 μm.

Preferably, the gradient composite coating has a total thickness of 180-660 μm; preferably 330-660 μm.

More preferably, the matrix structure is one or more of pearlite, martensite, ferrite, bainite, austenite and sorbite according to different heat treatment methods; preferably, the gradient composite coating is Applied to carbon steel surfaces.

The invention provides a method for preparing a guard rail, wherein the surface of the guard rail is provided with a wear-resistant coating, comprising the following steps:

1. Prepare a tungsten plate first. Preferably, the purity of tungsten should be controlled at 99.7-99.99%. Preferably, the tungsten plate is surface-treated first; preferably, the thickness of the tungsten plate is 0.2-3mm;

2. Make the guard rail lost foam according to the size of the guard rail. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. Fix the tungsten plate on the surface, and then fix an external carbon source on the surface of the tungsten plate so that it is closely combined with the tungsten plate; preferably, use polystyrene foam to make the guardrail lost foam; preferably, the external carbon source is graphite paper, Graphite paper is above grade 3, with a purity of 99%, and a thickness of 0.1-0.35mm;

3. Make sand molds according to the size of the guard rails, one guard rail for each box, and two boxes for splitting. Put the lost foam of the guard rails together with the tungsten plate and the external carbon source in the sand mold cavity; preferably, harden with CO ₂ water glass Sand, coated sand, self-setting resin sand or green sand to make sand molds;

4. Smelting the carbon steel substrate into molten steel; preferably, the temperature is controlled at 1610-1630°C;

5. Using the lost foam vacuum suction casting process, the above molten steel is poured into the above-mentioned sand mold with the guard rail mold, tungsten plate and carbon source placed. After the molten steel is cooled and solidified, the casting is taken out and the sand is cleaned to obtain the guard rail matrix It is a carbon steel matrix, and the working surface of the guard rail is a composite of carbon steel and tungsten plate; preferably, the pouring temperature is controlled at 1610-1630°C; more preferably, the pouring time is 40-50 seconds; further preferably, a Minutes later, top up the riser; preferably, cool to room temperature.

6. Put the guard rail complex obtained after casting into a heat preservation furnace with a protective atmosphere for heat preservation, and finally cool with the furnace to form a wear-resistant coating on the surface of the guard rail, while the guard rail matrix is still a carbon steel matrix.

Among them, the wear-resistant coating is a WC dense ceramic layer.

Preferably, the WC dense ceramic layer is obtained by controlling the holding time and holding temperature in step 6); preferably, the WC dense ceramic layer is a quasi-single crystal phase, and the quasi-single crystal phase refers to a phase between a polycrystalline phase and a single crystal phase. Among the crystal phases, compared with the polycrystalline phase, the crystal orientation is highly consistent, the grain boundaries are significantly reduced, and the atomic arrangement is relatively orderly.

The present invention also provides a method for preparing a guard rail, which has a gradient composite coating on the body, comprising the following steps:

1. Prepare a tungsten plate first, preferably, wherein the purity of tungsten is controlled at 99.7-99.99%. Preferably, the thickness of the tungsten plate is 0.2-3mm;, preferably, the tungsten plate is first surface-treated;

2. Make the guard rail lost foam according to the size of the guard rail. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. Fix the tungsten plate on the surface, and then fix an external carbon source on the surface of the tungsten plate to make it closely bonded to the tungsten plate; preferably, use polystyrene foam to make the guard rail lost foam;

3. Make sand molds according to the size of the guard rails, one guard rail for each box, and two boxes for splitting. Put the guard rails together with the tungsten plate and the external carbon source in the sand mold cavity; preferably, use CO ₂ water glass to harden the sand, Coated sand, self-setting resin sand or green sand to make sand molds;

4. Smelting the carbon steel substrate into molten steel; preferably, the temperature is controlled at 1610-1630°C;

5. Using the lost foam vacuum suction casting process, the above molten steel is poured into the above-mentioned sand mold with the guard rail mold, tungsten plate and carbon source placed. After the molten steel is cooled and solidified, the casting is taken out and the sand is cleaned to obtain the guard rail matrix It is a carbon steel matrix, and the working surface of the guard rail is a composite of carbon steel and tungsten plate; preferably, the pouring temperature is controlled at 1610-1630°C; preferably, the pouring time is 40-50 seconds; more preferably, one minute Finally, add pouring at the riser; preferably, after cooling at room temperature, after the molten steel is cooled and solidified, the casting is taken out, sand-cleaned, and the guard rail matrix obtained is a carbon steel matrix, and the working surface of the guard rail is a composite of carbon steel and tungsten plate body;

6. Put the coated outer carbon source of the guard rail complex obtained after casting into a heat preservation furnace with a protective atmosphere to keep warm, and finally cool with the furnace, so as to form a gradient composite coating on the surface of the guard rail head and rail waist, and the guard rail The rail matrix is still a carbon steel matrix.

7. The resulting guard rail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure.

Preferably, the thickness of the titanium plate is 0.2-3mm; if it is less than 0.2mm, the tungsten plate has completely reacted during the casting and compounding process, and the WC dense ceramic layer cannot be obtained, and the WC particles in a dispersed distribution are directly generated; if it exceeds 3mm, the diffusion distance will increase. Big and underpowered.

Preferably, in step 6, the dense ceramic layer of quasi-single crystal phase WC is obtained by strictly controlling the relationship between the holding temperature and time. The ceramic layer presents a relatively obvious quasi-single crystal structure. Under the optical microscope, it shows that the grain boundaries are reduced, and the dislocations affecting the fracture toughness are also correspondingly reduced. Instead, the subgrain boundaries are increased, which effectively improves the crack resistance of the ceramic layer.

Preferably, by controlling the holding time and holding temperature in step 6), the gradient composite coating, that is, the carbide coating, is obtained, and the carbide coating includes a quasi-single crystal phase WC dense ceramic layer, a micron WC ceramic layer, and a gradient distribution in sequence. layer, the fusion layer of WC and matrix.

More preferably, the total thickness of the gradient composite coating that can be finally obtained at the holding temperature, the holding time and the gradient composite coating conforms to the following formula

L＝kTlogt ^1/2 +b ₀

in:

L——the total thickness of the gradient composite coating (μm),

k——is a constant, the value is 0-1, k≠0,

T - reaction temperature,

t—response time,

b ₀ ——response initial thickness, that is, the thickness of the composite layer formed between the molten steel and the tungsten plate after pouring.

In summary, the gradient composite coating, including the WC dense ceramic layer, has high hardness. The WC dense ceramic layer is a quasi-single crystal phase, and the quasi-single crystal phase means that the arrangement of atoms does not have the same lattice as a general single crystal, but still has a strict order, showing a geometric arrangement; crystal orientation The consistency is high, the grain boundaries are significantly reduced, and the atomic arrangement is relatively orderly. The quasi-single crystal phase is between the polycrystalline phase and the single crystal phase. Compared with the polycrystalline phase, the grain boundaries of the quasi-single crystal phase are significantly reduced, the dislocation density is low, and there are more sub-grain boundaries, so the hardness is significantly improved. ; Compared with the single crystal phase, it has lower requirements on the preparation method, and the structure is more stable.

Preferably, in step 1), the steps of surface treatment are as follows:

In the first step of pickling, choose 300ml/L hydrochloric acid or 60ml/L phosphoric acid or 120ml/L hydrogen peroxide, and then rinse with running water;

In the second step of pickling, choose 300ml/L hydrofluoric acid or 200ml/L sulfuric acid or 240ml/L hydrogen peroxide, and then rinse with running water;

The third step is to polish the surface, choose 800 mesh or finer Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol.

More preferably, the external carbon source in step 2 is graphite paper; preferably, the graphite paper is above grade three, with a purity of 99%, and a thickness of 0.1-0.35 mm.

Preferably, in step 6), the temperature is raised to 1000-1140°C, the temperature rise rate is controlled at 7°C/min, and the holding time is 2-8h, preferably 4-8h.

Preferably, the selected carbon steel matrix is low carbon steel, medium carbon steel or high carbon steel.

Preferably, the protective gas is argon or nitrogen, and the gas flow rate is 4-8ml/min.

Among them, the holding temperature should be strictly controlled within the above range. If the temperature is higher than 1140°C, there will be too much liquid phase in the reaction process, so that the bulk quasi-phase single crystal WC will directly generate dispersed WC particles, and the quasi-single crystal cannot be obtained. Phase-dense WC ceramic layer; but the temperature is lower than 1000 ° C, the solubility of W is too low, and the reaction cannot proceed forward. Similarly, the holding time should also be maintained in a reasonable interval. If the time exceeds 8 hours, the dense WC ceramic layer in the quasi-single crystal phase will disappear, and the reaction will diffuse to form the fusion of dispersed WC particles and the matrix. If it is less than 2 hours, the WC obtained by the reaction will be too large. Less, the thickness of the coating is difficult to guarantee, the best should be kept at 4-8h.

More preferably, the carbon steel composite with carbide coating is further heat-treated to obtain a more suitable matrix structure: heat treatment at 550-800°C, the matrix is pearlite structure; heat treatment at 220-450°C, the matrix is shellfish Tensite structure; heat treatment below 220 ℃, the matrix is martensite structure.

The guard rail uses carbon steel as the matrix, and the selected carbon steel matrix is low-carbon steel, medium-carbon steel and high-carbon steel, preferably: Q275A, Q255AF, 45 steel, T12A, T8, ZG270-450, etc., see national standards GB221-79. The matrix structure is one or more of pearlite, martensite, ferrite, bainite, austenite and sorbite according to different heat treatment methods.

In the present invention, after the steel-tungsten composite body is obtained by casting, an external carbon source is introduced, and a carbide coating can be directly formed on the surface of the working part of the guard rail by means of heating and diffusion. Very strong, overcomes the problem of non-metallurgical bonding between the existing hard particles and the metal matrix, the bonding force is weak, and the particles are easy to fall off, and the mechanical properties of the coating are greatly improved. Moreover, the method is simple to operate, does not require complex equipment, and the obtained guard rail has good performance. Different heat treatment methods make the working surface of the guard rail and the substrate itself have different mechanical properties, which meet the different performance requirements of each part in actual production. Due to the formation of a dense quasi-single crystal ceramic layer on the surface, the ceramic layer presents a more obvious quasi-single crystal structure. Under the optical microscope, the grain boundaries are reduced, and the dislocations that affect the fracture toughness are correspondingly reduced, and the subgrain boundaries are increased instead. Effectively improve the crack resistance of the ceramic layer. Therefore, the maximum hardness of the guard rail surface can reach 2000-2400HV _0.05 , and the relative wear resistance is 10-22 times that of the matrix. The definition of described relative wear resistance is: take base material as standard sample, under the same load, the ratio of the wear amount produced by the measured coating to the wear amount produced by the standard sample is called the relative wear resistance of the coating, so It is also referred to as the relative wear resistance of the coating several times that of the substrate, and the same parameter testing standards as described below are the same.

This is because the WC dense ceramic layer is a quasi-single crystal structure, has good chemical stability and wear resistance, and has low friction coefficient, high hardness, low surface energy and low heat transfer. In contrast, the hardness of the micron WC ceramic layer can only reach 1200-2000HV _0.05 , and its relative wear resistance is 6-10 times that of the matrix.

Description of drawings

Fig. 1 is the layout diagram of the outer carbon source and the tungsten plate on the outer wall of the wear-resistant pipe lost foam before casting;

Figure 2 is a composite guard rail after heat treatment and a schematic diagram of the organization of each part;

Fig. 3 is a microstructure diagram of a quasi-single crystal phase WC dense ceramic layer;

Fig. 4 is a microstructure diagram of a micron WC ceramic layer.

In the figure, 1. graphite paper, 2. tungsten plate, 3. WC dense ceramic layer, 4. micron WC ceramic layer, 5. fusion layer of WC and substrate, 6. substrate, 7. sand mold, 8. guard rail lost foam .

Detailed ways

Preferred embodiments of the present invention are described below, and it should be understood that the preferred embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

Embodiment 1: the preparation method of guard rail, comprises the steps:

1. First prepare a tungsten plate 2, in which the purity of tungsten should be controlled at 99.7%. The tungsten plate 2 should be surface treated first, the steps are as follows:

The first step is pickling, choose 300ml/L hydrochloric acid, and then rinse with running water;

In the second step of pickling, choose 300ml/L hydrofluoric acid, and then rinse with running water;

The third step is to polish the surface, use 800 mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol. The thickness of the tungsten plate 2 is controlled at 0.2mm.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. Fix the tungsten plate on the surface of the rail head and the rail waist of the lost foam, and then fix the graphite paper 1 on the surface of the tungsten plate so that it is closely combined with the tungsten plate, as shown in Figure 1. The graphite paper 1 is above grade three, with a purity of 99%, and a thickness of 0.1mm.

3. According to the size of the guard rail, use _CO2 water glass hardened sand to make the sand mold 7, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7 middle;

4. The carbon steel substrate is smelted into molten steel, the temperature is controlled at 1630°C, and the selected carbon steel substrate is low carbon steel Q275A.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1630°C, and the pouring time is preferably 40 seconds. Minutes later, add pouring at the riser, after cooling at room temperature, after the molten steel is cooled and solidified, take out the casting, clean the sand, and obtain the guard rail matrix as a carbon steel matrix, and the working surface of the guard rail is a composite of carbon steel and tungsten plate;

6. Put the guard rail complex obtained after casting into a holding furnace with a protective atmosphere to keep warm, raise the temperature to 1000°C, control the heating rate at 7°C/min, hold the heat for 2 hours, and finally cool to room temperature with the furnace, so that the A gradient composite coating is formed on the surface of the guard rail head and rail waist, while the guard rail matrix is still a low carbon steel Q275A matrix. The protective gas is argon, and the gas flow rate is 5ml/min.

7. The obtained guard rail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure. The heat treatment process is: heat treatment below 220° C., and the matrix 6 is a martensitic structure.

The gradient composite coating includes a WC dense ceramic layer 3, which is a quasi-single crystal phase, with a particle size of 10 μm; along the longitudinal section of the coating, its thickness is 50 μm, and the volume fraction of WC is 85%.

Further, it also includes a micron WC ceramic layer 4 located under the above-mentioned quasi-single crystal WC dense ceramic layer 3, along the longitudinal section of the coating, its thickness is 70 μm, the volume fraction of WC is 80%, and its particle size is 5 μm.

Furthermore, it also includes the fusion layer 5 of WC and the substrate under the above-mentioned quasi-single crystal WC dense ceramic layer 3 and the micron WC ceramic layer 4, along the longitudinal section of the coating, its thickness is 60 μm, and the volume fraction of WC is 80%, and its particle size is 1 μm. At this time, the carbide coating is a composite coating, as shown in Figure 2, which can be composed of a quasi-single crystal WC dense ceramic layer 3, a micron WC ceramic layer 4, and a fusion layer 5 between WC and the substrate, and is sequentially formed from the outside to the inside. Gradient distribution with a total thickness of 180 μm. The Q275A carbon steel matrix is martensite. The hardness of the surface of the guard rail is 2000HV _0.05 , and the relative wear resistance is 14 times that of the steel matrix.

Embodiment 2: the preparation method of guard rail, comprises the steps:

1. Prepare a tungsten plate 2 first, wherein the purity of tungsten should be controlled at 99.8%. The tungsten plate 2 should be surface treated first, and the thickness of the tungsten plate 2 should be controlled at 0.8mm. Proceed as follows:

The first step is pickling, 60ml/L phosphoric acid, and then rinse with running water;

The second step is pickling, 200ml/L sulfuric acid, and then rinse with running water;

The third step is to polish the surface with 1000-mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. The tungsten plate is fixed on the surface of the rail head and the rail waist of the lost foam, and then the graphite paper 1 is fixed on the surface of the tungsten plate so that it is closely combined with the tungsten plate. The graphite paper 1 is above grade three, with a purity of 99%, and a thickness of 0.2mm.

3. According to the size of the guard rail, make the sand mold 7 with coated sand, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7.

4. The carbon steel substrate is smelted into molten steel, the temperature is controlled at 1630°C, and the selected carbon steel substrate is low carbon steel Q255AF.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1630°C, and the pouring time is preferably 45 seconds. Minutes later, add pouring at the riser, cool at room temperature, and after the molten steel is cooled and solidified, take out the casting and clean the sand to obtain a carbon steel base for the guard rail, and a composite of carbon steel and tungsten plate on the working surface of the guard rail.

6. Put the guard rail complex obtained after casting into a holding furnace with a protective atmosphere to keep warm, raise the temperature to 1050°C, control the heating rate at 7°C/min, hold the heat for 4 hours, and finally cool to room temperature with the furnace, so that the A gradient composite coating is formed on the surface of the guard rail head and rail waist, while the base of the guard rail is still a low carbon steel Q255AF base. The protective gas is nitrogen, and the gas flow rate is 6ml/min.

7. The obtained guard rail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure. The heat treatment process is: heat treatment at 650° C., and the matrix 6 is pearlite structure.

The gradient composite coating includes a WC dense ceramic layer 3, as shown in Figure 3, which is a quasi-single crystal phase with a particle size of 30 μm; along the longitudinal section of the coating, its thickness is 130 μm; wherein the volume fraction of WC is 80 %.

Further, it includes a micron WC ceramic layer 4 located under the above-mentioned quasi-single crystal WC dense ceramic layer 3, as shown in Figure 4, along the longitudinal section of the coating, its thickness is 150 μm, and the volume fraction of WC is 75%. The diameter size is 15 μm.

Furthermore, it also includes a fusion layer 5 of WC and substrate located under the above-mentioned quasi-single crystal WC dense ceramic layer 3 and micron WC ceramic layer 4, along the longitudinal section of the coating, its thickness is 200 μm, wherein the volume fraction of WC is 65%, and its particle size is 10 μm. At this time, the carbide coating is a composite coating, which can be composed of the quasi-single crystal WC dense ceramic layer 3, the micron WC ceramic layer 4, and the fused layer 5 of WC and the substrate, and is distributed in a gradient from outside to inside. The total thickness is 480 μm. The Q255AF carbon steel matrix is pearlite. The hardness of the guard rail surface is 2150HV _0.05 , and the wear resistance is 15 times that of the steel matrix.

Embodiment 3: the preparation method of guard rail, comprises the steps:

1. Prepare a tungsten plate 2 first, wherein the purity of the tungsten is controlled at 99.8%, and the thickness of the tungsten plate 2 is controlled at 1mm. The tungsten plate 2 should be surface treated first, the steps are as follows:

The first step is pickling, 120ml/L hydrogen peroxide, and then rinse with running water;

The second step is pickling, 240ml/L hydrogen peroxide, and then rinse with running water;

The third step is to polish the surface with 1000-mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. The tungsten plate is fixed on the surface of the rail head and the rail waist of the lost foam, and then the graphite paper 1 is fixed on the surface of the tungsten plate so that it is closely combined with the tungsten plate. The graphite paper 1 is above grade three, with a purity of 99% and a thickness of 0.35mm.

3. According to the size of the guard rail, make the sand mold 7 with self-setting resin sand, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7.

4. The carbon steel substrate is smelted into molten steel, the temperature is controlled at 1620°C, and the selected carbon steel substrate is medium carbon steel 45 steel.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1620°C, and the pouring time is preferably 50 seconds. Minutes later, add pouring at the riser, cool at room temperature, and after the molten steel is cooled and solidified, take out the casting and clean the sand to obtain a carbon steel base for the guard rail, and a composite of carbon steel and tungsten plate on the working surface of the guard rail.

6. Put the guard rail complex obtained after casting into a holding furnace with a protective atmosphere to keep warm, raise the temperature to 1100°C, control the heating rate at 7°C/min, hold the heat for 4 hours, and finally cool down to room temperature with the furnace, so that the A gradient composite coating is formed on the surface of the guard rail head and rail waist, while the guard rail matrix is still a medium carbon steel 45 steel matrix. The protective gas is nitrogen, and the gas flow rate is 6ml/min.

7. The obtained guardrail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure. The heat treatment is carried out at 700° C., and the matrix 6 is a pearlite structure.

The gradient composite coating includes WC dense ceramic layer 3, which is a quasi-single crystal phase, and its particle size is 35 μm; along the longitudinal section of the coating, its thickness is 160 μm, and the volume fraction of WC is 80%.

Further, the micron WC ceramic layer 4 located under the quasi-single crystal WC dense ceramic layer 3 has a thickness of 170 μm along the longitudinal section of the coating, a volume fraction of WC of 75%, and a particle size of 20 μm.

Furthermore, it also includes the fusion layer 5 of WC and the substrate under the above-mentioned quasi-single crystal WC dense ceramic layer 3 and the micron WC ceramic layer 4, along the longitudinal section of the coating, its thickness is 260 μm, wherein the volume fraction of WC is 50%, and its particle size is 16 μm. At this time, the carbide coating is a composite coating, which can be composed of the quasi-single crystal WC dense ceramic layer 3, the micron WC ceramic layer 4, and the fused layer 5 of WC and the substrate, and is distributed in a gradient from outside to inside. The total thickness is 590 μm, and the 45 steel carbon steel matrix is pearlite. The hardness of the guard rail surface is 2200HV _0.05 , and the wear resistance is 16 times that of the steel matrix.

Embodiment 4: the preparation method of guard rail, comprises the steps:

1. Prepare a tungsten plate 2 first, wherein the purity of tungsten should be controlled at 99.99%. The tungsten plate 2 should be surface treated first, and the steps are as follows:

In the first step of pickling, choose 60ml/L phosphoric acid, and then rinse with running water;

The second step is pickling, 200ml/L sulfuric acid, and then rinse with running water;

The third step is to polish the surface, use 1200 mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol. The thickness of the tungsten plate 2 is controlled at 2mm.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. The tungsten plate is fixed on the surface of the rail head and the rail waist of the lost foam, and then the graphite paper 1 is fixed on the surface of the tungsten plate so that it is closely combined with the tungsten plate. The graphite paper 1 is above grade three, with a purity of 99% and a thickness of 0.15 mm.

3. According to the size of the guard rail, make the sand mold 7 with green sand, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7.

4. The carbon steel substrate is smelted into molten steel, the temperature is controlled at 1630°C, and the selected carbon steel substrate is low carbon steel Q275A.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1630°C, and the pouring time is preferably 50 seconds. Minutes later, add pouring at the riser, cool at room temperature, and after the molten steel is cooled and solidified, take out the casting and clean the sand to obtain a carbon steel base for the guard rail, and a composite of carbon steel and tungsten plate on the working surface of the guard rail.

6. Put the guard rail complex obtained after casting into a holding furnace with a protective atmosphere for heat preservation, raise the temperature to 1140°C, control the temperature rise rate at 7°C/min, keep the heat preservation time for 8h, and finally cool to room temperature with the furnace, so that the A gradient composite coating is formed on the surface of the guard rail head and rail waist, while the guard rail matrix is still a low carbon steel Q275A matrix. The protective gas is nitrogen, and the gas flow rate is 6ml/min.

7. The obtained guard rail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure. The heat treatment process is: heat treatment at 450° C., and the matrix 6 is a bainite structure.

The gradient composite coating includes WC dense ceramic layer 3, which is a quasi-single crystal phase, and its particle size is 45 μm; along the longitudinal section of the coating, its thickness is 180 μm; the volume fraction of WC is 85%.

Further, the micron WC ceramic layer 4 located under the quasi-single crystal WC dense ceramic layer 3 has a thickness of 180 μm along the longitudinal section of the coating, a volume fraction of WC of 75%, and a particle size of 30 μm.

Furthermore, it also includes the fusion layer 5 of WC and the substrate under the above-mentioned quasi-single crystal WC dense ceramic layer 3 and the micron WC ceramic layer 4, along the longitudinal section of the coating, its thickness is 300 μm, wherein the volume fraction of WC is 40%, and its particle size is 20 μm. In summary, the carbide coating is a composite coating, which is composed of the quasi-single crystal WC dense ceramic layer 3, the micron WC ceramic layer 4 and the fusion layer 5 of WC and the substrate, and is distributed in a gradient from outside to inside. Its total thickness is 660 μm. The Q275A carbon steel matrix is bainite. The hardness of the guard rail surface is 2400HV _0.05 , and the wear resistance is 22 times that of the steel matrix.

Embodiment 5: the preparation method of guard rail, comprises the steps:

1. First prepare a tungsten plate 2, in which the purity of tungsten should be controlled at 99.7%. The thickness of the tungsten plate 2 is controlled at 3mm. The tungsten plate 2 should be surface treated first, the steps are as follows:

The first step is pickling, choose 300ml/L hydrochloric acid, and then rinse with running water;

The second step is pickling, 240ml/L hydrogen peroxide, and then rinse with running water;

The third step is to polish the surface, use 800 mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. The tungsten plate is fixed on the surface of the rail head and the rail waist of the lost foam, and then the graphite paper 1 is fixed on the surface of the tungsten plate so that it is closely combined with the tungsten plate. The graphite paper 1 is above grade three, with a purity of 99% and a thickness of 0.25mm.

3. According to the size of the guard rail, use _CO2 water glass hardened sand to make the sand mold 7, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7 middle.

4. The carbon steel substrate is smelted into liquid steel, the temperature is controlled at 1620°C, and the selected carbon steel substrate is medium carbon steel 50 steel.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1620°C, and the pouring time is preferably 40 seconds. Minutes later, add pouring at the riser, cool at room temperature, and after the molten steel is cooled and solidified, take out the casting and clean the sand to obtain a carbon steel base for the guard rail, and a composite of carbon steel and tungsten plate on the working surface of the guard rail.

6. Put the guard rail complex obtained after casting into a holding furnace with a protective atmosphere to keep warm, raise the temperature to 1000°C, control the heating rate at 7°C/min, hold the heat for 8 hours, and finally cool down to room temperature with the furnace, so that the A gradient composite coating is formed on the surface of the guard rail head and rail waist, while the guard rail matrix is still a medium carbon steel 50 steel matrix. The protective gas is nitrogen, and the gas flow rate is 7ml/min.

7. The obtained guard rail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure. The heat treatment process is: heat treatment at 400° C., and the matrix 6 is a bainite structure.

The gradient composite coating includes WC dense ceramic layer 3, which is a quasi-single crystal phase, and its particle size is 25 μm; along the longitudinal section of the coating, its thickness is 150 μm; the volume fraction of WC is 85%.

Further, it includes a micron WC ceramic layer 4 located under the quasi-single crystal WC dense ceramic layer 3, along the longitudinal section of the coating, its thickness is 160 μm, the volume fraction of WC is 75%, and its particle size is 15 μm.

Furthermore, it also includes a fused layer 5 of WC and substrate located under the above-mentioned quasi-single crystal WC dense ceramic layer 3 and micron WC ceramic layer 4, along the longitudinal section of the coating, its thickness is 230 μm, wherein the volume fraction of WC is 75%, and its particle size is 9 μm. In summary, the carbide coating is a composite coating, which can be composed of the quasi-single crystal WC dense ceramic layer 3, the micron WC ceramic layer 4, and the fusion layer 5 of WC and the substrate, and is distributed in a gradient from outside to inside. The total thickness is 540 μm. The carbon steel matrix of the 50 steel is bainite. The hardness of the surface of the guard rail is 2100HV _0.05 , and the wear resistance is 14 times that of the steel matrix.

Embodiment 6: the preparation method of guard rail, comprises the steps:

1. Prepare a tungsten plate 2 first, wherein the purity of tungsten should be controlled at 99.99%, and the thickness of the tungsten plate 2 should be controlled at 2 mm. The tungsten plate 2 should be surface treated first, the steps are as follows:

The first step is pickling, choose 120ml/L hydrogen peroxide, and then rinse with running water;

The second step is pickling, 240ml/L hydrogen peroxide, and then rinse with running water;

The third step is to polish the surface, use 1200 mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. The tungsten plate is fixed on the surface of the rail head and the rail waist of the lost foam, and then the graphite paper 1 is fixed on the surface of the tungsten plate so that it is closely combined with the tungsten plate. The graphite paper 1 is above grade three, with a purity of 99% and a thickness of 0.25mm.

3. According to the size of the guard rail, make the sand mold 7 with coated sand, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7.

4. The carbon steel substrate is smelted into molten steel, the temperature is controlled at 1610°C, and the selected carbon steel substrate is high carbon steel T8.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1610°C, and the pouring time is preferably 50 seconds. Minutes later, add pouring at the riser, cool at room temperature, and after the molten steel is cooled and solidified, take out the casting and clean the sand to obtain a carbon steel base for the guard rail, and a composite of carbon steel and tungsten plate on the working surface of the guard rail.

6. Put the guard rail complex obtained after casting into a holding furnace with a protective atmosphere for heat preservation, raise the temperature to 1050°C, control the temperature rise rate at 7°C/min, and keep the heat preservation time for 2 hours, and finally cool to room temperature with the furnace, so that the A gradient composite coating is formed on the surface of the guard rail head and rail waist, while the guard rail matrix is still a high carbon steel T8 matrix. The protective gas is argon, and the gas flow rate is 8ml/min.

7. The obtained guard rail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure. The heat treatment process is: heat treatment below 220° C., and the matrix 6 is a martensitic structure.

The gradient composite coating includes a WC dense ceramic layer 3, which is a quasi-single crystal phase, and its particle size is 20 μm; along the longitudinal section of the coating, its thickness is 60 μm, and the volume fraction of WC is 85%.

Further, the micron WC ceramic layer 4 located under the quasi-single crystal WC dense ceramic layer 3 has a thickness of 80 μm along the longitudinal section of the coating, a volume fraction of WC of 80%, and a particle size of 10 μm.

Furthermore, it also includes the fusion layer 5 of WC and the substrate under the above-mentioned quasi-single crystal WC dense ceramic layer 3 and the micron WC ceramic layer 4, along the longitudinal section of the coating, its thickness is 70 μm, and the volume fraction of WC is 70%, and its particle size is 6 μm. In summary, the carbide coating is a composite coating, which can be composed of a quasi-single crystal WC dense ceramic layer 3, a micron WC ceramic layer 4, and a fusion layer 5 between WC and the substrate. is 210 μm. The T8 carbon steel matrix is martensite. The hardness of the guard rail surface is 2050HV _0.05 , and the wear resistance is 10 times that of the steel matrix.

Embodiment 7: the preparation method of guard rail, comprises the steps:

1. First prepare a tungsten plate 2, in which the purity of tungsten should be controlled at 99.9%. The tungsten plate 2 should be surface treated first, the steps are as follows:

In the first step of pickling, choose 60ml/L phosphoric acid, and then rinse with running water;

In the second step of pickling, choose 200ml/L sulfuric acid, and then rinse with running water.

The third step is to polish the surface, use 1000 mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol.

The thickness of the tungsten plate 2 is controlled at 1mm.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. The tungsten plate is fixed on the surface of the rail head and the rail waist of the lost foam, and then the graphite paper 1 is fixed on the surface of the tungsten plate so that it is closely combined with the tungsten plate. The graphite paper 1 is above grade three, with a purity of 99% and a thickness of 0.15mm.

3. According to the size of the guard rail, make the sand mold 7 with self-setting resin sand, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7.

4. The carbon steel substrate is smelted into molten steel, the temperature is controlled at 1630°C, and the selected carbon steel substrate is low carbon steel ZG270-500.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1630°C, and the pouring time is preferably 45 seconds. Minutes later, add pouring at the riser, cool at room temperature, and after the molten steel is cooled and solidified, take out the casting and clean the sand to obtain a carbon steel base for the guard rail, and a composite of carbon steel and tungsten plate on the working surface of the guard rail.

6. Put the guard rail complex obtained after casting into a holding furnace with a protective atmosphere for heat preservation, raise the temperature to 1100°C, control the temperature rise rate at 7°C/min, keep the heat preservation time for 2h, and finally cool down to room temperature with the furnace, so that the A gradient composite coating is formed on the surface of the guard rail head and rail waist, while the guard rail matrix is still a low carbon steel ZG270-500 matrix. The protective gas is nitrogen, and the gas flow rate is 8ml/min.

7. The obtained guard rail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure, and the heat treatment is performed below 600°C, and the matrix 6 is pearlite structure.

The gradient composite coating includes WC dense ceramic layer 3, which is a quasi-single crystal phase, and its particle size is 30 μm; along the longitudinal section of the coating, its thickness is 80 μm; the volume fraction of WC is 85%.

Further, it includes a micron WC ceramic layer 4 located under the bulk quasi-single crystal WC dense ceramic layer 3, along the longitudinal section of the coating, its thickness is 90 μm, the volume fraction of WC is 80%, and its particle size is 15 μm.

Furthermore, it also includes a fused layer 5 of WC and substrate located under the above-mentioned quasi-single crystal WC dense ceramic layer 3 and micron WC ceramic layer 4, along the longitudinal section of the coating, its thickness is 80 μm, wherein the volume fraction of WC is 55%, and its particle size is 15 μm. In summary, the carbide coating is a composite coating, which can be composed of the quasi-single crystal WC dense ceramic layer 3, the micron WC ceramic layer 4, and the fusion layer 5 of WC and the substrate, and is distributed in a gradient from outside to inside. The total thickness is 230 μm. The ZG270-500 carbon steel matrix is pearlite. The hardness of the surface of the guard rail is 2150HV _0.05 , and the wear resistance is 15 times that of the ZG270-500 steel matrix.

Embodiment 8: the preparation method of guard rail, comprises the steps:

1. Prepare a tungsten plate 2 first, in which the purity of tungsten should be controlled at 99.8%. The thickness of the tungsten plate 2 is controlled at 3mm. The tungsten plate 2 should be surface treated first, the steps are as follows:

The first step is pickling, choose 120ml/L hydrogen peroxide, and then rinse with running water;

In the second step of pickling, choose 240ml/L hydrogen peroxide, and then rinse with running water.

The third step is to polish the surface, use 1200 mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. The tungsten plate is fixed on the surface of the rail head and the rail waist of the lost foam, and then the graphite paper 1 is fixed on the surface of the tungsten plate so that it is closely combined with the tungsten plate. The graphite paper 1 is above grade three, with a purity of 99%, and a thickness of 0.3 mm.

3. According to the size of the guard rail, make the sand mold 7 with green sand, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7.

4. The carbon steel substrate is smelted into molten steel, the temperature is controlled at 1620°C, and the selected carbon steel substrate is medium carbon steel 45 steel.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1620°C, and the pouring time is preferably 45 seconds. Minutes later, add pouring at the riser, cool at room temperature, and after the molten steel is cooled and solidified, take out the casting and clean the sand to obtain a carbon steel base for the guard rail, and a composite of carbon steel and tungsten plate on the working surface of the guard rail.

6. Put the composite obtained after casting into a holding furnace with a protective atmosphere for heat preservation, raise the temperature to 1120°C, control the temperature rise rate at 7°C/min, and hold the heat for 8 hours, and finally cool down to room temperature with the furnace, so that Gradient composite coating is formed on the surface of rail head and rail waist, while the matrix of guard rail is still medium carbon steel 45 steel matrix. The protective gas is nitrogen, and the gas flow rate is 6ml/min.

7. The obtained guard rail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure. The heat treatment is carried out at 550° C., and the matrix 6 is pearlite structure.

The gradient composite coating includes WC dense ceramic layer 3, which is a quasi-single crystal phase, and its particle size is 40 μm; along the longitudinal section of the coating, its thickness is 170 μm; the volume fraction of WC is 80%.

Further, the micron WC ceramic layer 4 located under the quasi-single crystal WC dense ceramic layer 3 has a thickness of 170 μm along the longitudinal section of the coating, a volume fraction of WC of 75%, and a particle size of 25 μm.

Furthermore, it also includes the fusion layer 5 of WC and the substrate under the above-mentioned bulk quasi-single crystal WC dense ceramic layer 3 and the micron WC ceramic layer 4. Along the longitudinal section of the coating, its thickness is 280 μm, wherein the volume fraction of WC It is 45%, and its particle size is 18 μm. In summary, the carbide coating is a composite coating, which can be composed of the quasi-single crystal WC dense ceramic layer 3, the micron WC ceramic layer 4, and the fusion layer 5 of WC and the substrate, and is distributed in a gradient from outside to inside. The total thickness is 630 μm, and the 45 steel carbon steel matrix is pearlite. The hardness of the surface of the guard rail is 2300HV _0.05 , and the wear resistance is 18 times that of the steel matrix.

Embodiment 9: the preparation method of guard rail, comprises the steps:

1. Prepare a tungsten plate 2 first, in which the purity of tungsten should be controlled at 99.8%. The tungsten plate 2 should be surface treated first, the steps are as follows:

In the first step of pickling, choose 60ml/L phosphoric acid, and then rinse with running water;

In the second step of pickling, choose 200ml/L sulfuric acid, and then rinse with running water;

The third step is to polish the surface, use 1000 mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol. The thickness of the tungsten plate 2 is controlled at 1.5mm.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. The tungsten plate is fixed on the surface of the rail head and the rail waist of the lost foam, and then the graphite paper 1 is fixed on the surface of the tungsten plate so that it is closely combined with the tungsten plate. The graphite paper 1 is above grade three, with a purity of 99%, and a thickness of 0.2mm.

3. According to the size of the guard rail, use _CO2 water glass hardened sand to make the sand mold 7, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7 middle.

4. The carbon steel substrate is smelted into molten steel, the temperature is controlled at 1630°C, and the selected carbon steel substrate is low carbon steel Q275A.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1630°C, and the pouring time is preferably 40 seconds. Minutes later, add pouring at the riser, cool at room temperature, and after the molten steel is cooled and solidified, take out the casting and clean the sand to obtain a carbon steel base for the guard rail, and a composite of carbon steel and tungsten plate on the working surface of the guard rail.

6. Put the composite obtained after casting into a holding furnace with a protective atmosphere for heat preservation, raise the temperature to 1000°C, control the heating rate at 7°C/min, keep the heat for 4 hours, and finally cool down to room temperature with the furnace, so that the guard rail Gradient composite coating is formed on the surface of rail head and rail waist, while the base of guard rail is still low carbon steel Q275A base. The protective gas is nitrogen, and the gas flow rate is 6ml/min.

7. The obtained guardrail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure. The heat treatment is carried out at 450° C., and the matrix 6 is a bainite structure.

The gradient composite coating includes WC dense ceramic layer 3, which is a quasi-single crystal phase, and its particle size is 15 μm; along the longitudinal section of the coating, its thickness is 70 μm; the volume fraction of WC is 85%.

Further, the micron WC ceramic layer 4 located under the quasi-single crystal WC dense ceramic layer 3 has a thickness of 80 μm along the longitudinal section of the coating, a volume fraction of WC of 80%, and a particle size of 10 μm.

Furthermore, it also includes a fused layer 5 of WC and the substrate located under the bulk quasi-single crystal WC dense ceramic layer 3 and the micron WC ceramic layer 4. Along the longitudinal section of the coating, its thickness is 60 μm, wherein the volume fraction of WC It is 75%, and its particle size is 5 μm. In summary, the carbide coating is a composite coating, which is composed of the quasi-single crystal WC dense ceramic layer 3, the micron WC ceramic layer 4 and the fusion layer 5 of WC and the substrate, and is distributed in a gradient from outside to inside. The total thickness is 210 μm. The Q275A matrix is bainite. The hardness of the guard rail surface is 2050HV _0.05 , and the wear resistance is 12 times that of the steel matrix.

Embodiment 10: the preparation method of guard rail, comprises the steps:

1. First prepare a tungsten plate 2, in which the purity of tungsten should be controlled at 99.9%. The tungsten plate 2 should be surface treated first, the steps are as follows:

In the first step of pickling, choose 60ml/L phosphoric acid, and then rinse with running water;

In the second step of pickling, choose 200ml/L sulfuric acid, and then rinse with running water.

The third step is to polish the surface, use 900 mesh Al ₂ O ₃ sandpaper, and finally clean it ultrasonically with alcohol. The thickness of the tungsten plate 2 is controlled at 3mm.

2. According to the size of the guard rail, use polystyrene foam to make the lost foam of the guard rail 8. According to the working force of the guard rail, the main wear parts are the rail head and the rail waist surface of the guard rail. The tungsten plate is fixed on the surface of the rail head and the rail waist of the lost foam, and then the graphite paper 1 is fixed on the surface of the tungsten plate so that it is closely combined with the tungsten plate. The graphite paper 1 is above grade three, with a purity of 99%, and a thickness of 0.1mm.

3. According to the size of the guard rail, make the sand mold 7 with coated sand, one guard rail for each box, and two boxes for splitting. Put the guard rail lost foam 8 together with the tungsten plate and graphite paper 1 into the cavity of the sand mold 7.

4. The carbon steel substrate is smelted into molten steel, the temperature is controlled at 1620°C, and the selected carbon steel substrate is medium carbon steel 45 steel.

5. Using the lost foam vacuum suction casting process, pour the above molten steel into the above sand mold 7 with the guard rail mold, tungsten plate and graphite paper 1, the pouring temperature is controlled at 1620°C, and the pouring time is preferably 50 seconds. Minutes later, add pouring at the riser, cool at room temperature, and after the molten steel is cooled and solidified, take out the casting and clean the sand to obtain a carbon steel base for the guard rail, and a composite of carbon steel and tungsten plate on the working surface of the guard rail.

6. Put the composite obtained after casting into a holding furnace with a protective atmosphere for heat preservation, raise the temperature to 1050°C, control the temperature rise rate at 7°C/min, and hold the heat for 8 hours, and finally cool down to room temperature with the furnace, so that Gradient composite coating is formed on the surface of rail head and rail waist, while the matrix of guard rail is still medium carbon steel 45 steel matrix. The protective gas is nitrogen, and the gas flow rate is 6ml/min.

7. The obtained guardrail with gradient composite coating is further heat-treated to obtain a more suitable matrix structure. The heat treatment is carried out at 350° C., and the matrix 6 is a bainite structure.

The gradient composite coating includes WC dense ceramic layer 3, which is a quasi-single crystal phase, and its particle size is 35 μm; along the longitudinal section of the coating, its thickness is 180 μm; the volume fraction of WC is 80%.

Further, the micron WC ceramic layer 4 located under the quasi-single crystal WC dense ceramic layer 3 has a thickness of 170 μm along the longitudinal section of the coating, a volume fraction of WC of 75%, and a particle size of 20 μm.

Furthermore, it also includes a fused layer 5 of WC and substrate located under the above-mentioned quasi-single crystal WC dense ceramic layer 3 and micron WC ceramic layer 4, along the longitudinal section of the coating, its thickness is 280 μm, wherein the volume fraction of WC is 60%, and its particle size is 12 μm. In summary, the carbide coating is a composite coating, which can be composed of the quasi-single crystal WC dense ceramic layer 3, the micron WC ceramic layer 4, and the fusion layer 5 of WC and the substrate, and is distributed in a gradient from outside to inside. The total thickness is 630 μm. The carbon steel matrix of the 45 steel is bainite. The hardness of the surface of the guard rail is 2200HV _0.05 , and the wear resistance is 16 times that of the 45 steel matrix.

Comparative example 1, its preparation method is as follows: tungsten carbide particles are directly clad on the surface of carbon steel by laser cladding method to obtain a coating with a thickness of 30 μm and a volume fraction of 80%. The hardness of the obtained coating is 1650HV _0.05 , which is resistant to The abrasiveness is 2-3 times that of the steel matrix.

In the comparative example, the laser surface modification technology has high production costs, low production efficiency, difficult control of process parameters, and the use of adhesives during use will cause pores and slag inclusions; and there is no WC dense ceramic layer and micron WC ceramics in the composite layer layer, the thickness of the composite layer and the WC content are small, and the WC particle size is large; at the same time, the composite process is only to infiltrate the gap between the external hard chromium carbide particles and to melt and sinter the external particles, and the hard chromium carbide particles The non-metallurgical combination with the metal matrix has very weak binding force, and the particles are easy to fall off or have oxidation and inclusion problems. Therefore, its mechanical properties are poor.

Claims (21)

1. a guard rail, its surface has wear-resistant coating, it is characterized in that: described wear-resistant coating is WC dense ceramic layers.

2. guard rail as claimed in claim 1, is characterized in that: WC dense ceramic layers is as the criterion monocrystalline phase, and described accurate monocrystalline refers to mutually, between polycrystalline phase with monocrystalline phase, compared to polycrystalline phase, uniform orientation is high, crystal boundary obviously reduces, and the microscopic structure that atomic arrangement is more orderly.

3. guard rail as claimed in claim 1 or 2, it is characterized in that: along coating longitudinal profile, its thickness is 50-180 μm, is preferably 100-180 μm; Preferably, wherein the volume fraction of WC is greater than 80%, is preferably greater than 85%; Preferably, its particle diameter is 10-50 μm, is preferably 20-50 μm.

4. a guard rail, its surface has gradient composite coating, it is characterized in that: described gradient composite coating is carbide coating, comprises the fused layer of the WC dense ceramic layers of distribution gradient successively, micron WC ceramic layer, WC and matrix.

5. guard rail as claimed in claim 4, is characterized in that: WC dense ceramic layers is as the criterion monocrystalline phase, and described accurate monocrystalline refers to mutually, between polycrystalline phase with monocrystalline phase, compared to polycrystalline phase, uniform orientation is high, crystal boundary obviously reduces, and the microscopic structure that atomic arrangement is more orderly.

6. the guard rail as described in claim 4 or 5, is characterized in that: along WC dense ceramic layers longitudinal profile, and its thickness is 50-180 μm, is preferably 100-180 μm; Preferably, wherein the volume fraction of WC is greater than 80%, is preferably greater than 85%; Preferably, its particle diameter is 10-50 μm, is preferably 20-50 μm.

7. the guard rail as described in one of claim 4-6, it is characterized in that: along micron WC ceramic layer longitudinal profile, its thickness is 70-180 μm, be preferably 130-180 μm, preferably, the volume fraction of WC is greater than 75%, be preferably greater than 80%, preferably, the particle diameter of WC is 5-30 μm, is preferably 6-25 μm.

8. the guard rail as described in one of claim 4-7, it is characterized in that: along the fused layer longitudinal profile of WC and matrix, its thickness is 60-300 μm, preferred 100-300 μm, preferably, wherein the volume fraction of WC is 40%-80%, be preferably 60%-80%, preferably, the particle diameter of WC is 1-20 μm, is preferably 5-10 μm.

9. the guard rail as described in one of claim 4-8, is characterized in that: gradient composite coating gross thickness is 180-660 μm, more preferably at 330-660 μm.

10. the guard rail as described in one of claim 4-9, is characterized in that: matrix is not all one or more in pearlite, martensite, ferrite, bainite, austenite and sorbite according to heat treatment; Preferably, this gradient composite coating is applied in steel surface.

The preparation method of 11. 1 kinds of guard rails as described in one of claim 1-3, is characterized in that, guard rail surface has wear-resistant coating, comprises the steps:

1), first prepare a tungsten plate, preferably, wherein the purity of tungsten should control at 99.7-99.99%, and preferably, described tungsten plate thickness is 0.2-3mm; Preferably, tungsten plate is first by addition surface treatment;

2), guard rail evaporative pattern is made according to guard rail size, according to the work force-bearing situation of guard rail, the position of its key wear is rail head and the web of the rail surface of guard rail, accordingly at rail head and the web of the rail surface fixed tungsten plate of guard rail evaporative pattern, then in tungsten plate surface fixed outer carbon source, itself and tungsten plate are combined closely; Preferably, guard rail evaporative pattern is made with polystyrene foam plastics; Preferably, described external carbon source is graphite paper, and graphite paper is more than three grades, purity 99%, and thickness is 0.1-0.35mm;

3), according to guard rail size make sand mold, every case guard rail, two casees somatotypes, are placed in sand mold die cavity by guard rail in the lump together with tungsten plate and external carbon source; Preferably, CO is used ₂waterglass hardened sand, precoated sand, self-hardening resin sand or tide mould sand make sand mold;

4), carbon steel base material is smelted for molten steel; Preferably, temperature controls at 1610-1630 DEG C;

5), adopt evaporative pattern process for suction casting, above-mentioned molten steel is poured in the above-mentioned sand mold being placed with guard rail mould, tungsten plate and carbon source, after molten steel cooled and solidified, take out foundry goods, sand removal process, obtaining guard rail matrix is plain steel, and guard rail working surface is the complex of carbon steel and tungsten plate; Preferably, pouring temperature controls at 1610-1630 DEG C; Preferably, the duration of pouring is that 40-50 is advisable second; More preferably, after one minute, at hot topping; Preferably, room temperature cooling;

Step 6), the guard rail complex that obtains having cast puts into the holding furnace inside holding with protective atmosphere, finally cools to room temperature with the furnace, thus form wear resistant carbide coating on guard rail surface, and guard rail matrix is still plain steel;

Wherein, wear resistant carbide coating is WC dense ceramic layers.

The preparation method of 12. guard rails as claimed in claim 11, it is characterized in that: WC dense ceramic layers is as the criterion monocrystalline phase, described accurate monocrystalline refers to mutually, between polycrystalline phase with monocrystalline phase, compared to polycrystalline phase, uniform orientation is high, crystal boundary obviously reduces, and the microscopic structure that atomic arrangement is more orderly; Preferably, step 6) in obtain this WC dense ceramic layers by controlling temperature retention time, holding temperature.

The preparation method of 13. 1 kinds of guard rails as described in one of claim 4-10, is characterized in that, guard rail surface has gradient composite coating guard rail, comprises the steps:

1), first prepare a tungsten plate, preferably, wherein the purity of tungsten should control at 99.7-99.99%, and preferably, described tungsten plate thickness is 0.2-3mm; Preferably, tungsten plate 2 is first by addition surface treatment;

2), according to guard rail size, guard rail evaporative pattern is made with polystyrene foam plastics, according to the work force-bearing situation of guard rail, the position of its key wear is rail head and the web of the rail surface of guard rail, accordingly at rail head and the web of the rail surface fixed tungsten plate of guard rail evaporative pattern, then in tungsten plate surface fixed outer carbon source, itself and tungsten plate are combined closely; Preferably, guard rail evaporative pattern is made with polystyrene foam plastics;

3), according to guard rail size make sand mold, every case guard rail, two casees somatotypes, are placed in sand mold die cavity by guard rail in the lump together with tungsten plate and external carbon source; Preferably, CO is used ₂waterglass hardened sand, precoated sand, self-hardening resin sand or tide mould sand make sand mold;

4), carbon steel base material is smelted for molten steel; Preferably, temperature controls at 1610-1630 DEG C;

5), adopt evaporative pattern process for suction casting, above-mentioned molten steel is poured in the above-mentioned sand mold being placed with guard rail mould, tungsten plate and carbon source, after molten steel cooled and solidified, take out foundry goods, sand removal process, obtaining guard rail matrix is plain steel, and guard rail working surface is the complex of carbon steel and tungsten plate; Preferably, pouring temperature controls at 1610-1630 DEG C; Preferably, the duration of pouring is that 40-50 is advisable second; More preferably, after one minute, at hot topping; Preferably, room temperature cooling;

6) the guard rail complex, by having cast obtained puts into the holding furnace inside holding with protective atmosphere, finally cools to room temperature with the furnace, thus forms gradient composite coating at guard rail rail head and web of the rail surface, and guard rail matrix is still plain steel;

7), the guard rail with gradient composite coating of gained by further heat treatment to obtain more suitably matrix.

The preparation method of 14. guard rails as claimed in claim 13, it is characterized in that: by rate-determining steps 6) in temperature retention time, holding temperature obtain this gradient composite coating and carbide coating, described carbide coating comprises the fused layer of the accurate monocrystalline phase WC dense ceramic layers of distribution gradient successively, micron WC ceramic layer, WC and matrix.

The preparation method of 15. guard rails as claimed in claim 14, is characterized in that: holding temperature, temperature retention time and the gross thickness of gradient composite coating that finally can obtain meet following formula,

L＝kTlogt ^1/2+b ₀

Wherein:

The gross thickness (μm) of L---gradient composite coating,

K---be constant, value is 0-1, k ≠ 0,

T---reaction temperature (K),

T---the reaction time (s),

B ₀---reaction original depth (μm), the thickness of the composite bed formed after namely molten steel is poured into a mould and between tungsten plate.

The preparation method of 16. guard rails as described in one of claim 13-15, is characterized in that: described step 1) in, surface-treated step is as follows:

First step pickling, selects the hydrogen peroxide of the hydrochloric acid of 300ml/L or the phosphoric acid of 60ml/L or 120ml/L, rear running water;

Second step pickling, selects the hydrogen peroxide of the hydrofluoric acid of 300ml/L or the sulfuric acid of 200ml/L or 240ml/L, rear running water;

3rd step surface finish, selects 800 orders or thinner Al2O3 sand paper, finally uses alcohol ultrasonic cleaning.

The preparation method of 17. guard rails as described in one of claim 13-16, is characterized in that: described step 2) in external carbon source be graphite paper; Preferably, described graphite paper 1 is more than three grades, purity 99%, and thickness is 0.1-0.35mm.

The preparation method of 18. guard rails as described in one of claim 13-17, is characterized in that: described step 6) in, be warming up to 1000-1140 DEG C of insulation, preferably, programming rate controls at 7 DEG C/min, and temperature retention time is 2-8h, preferred 4-8h.

The preparation method of 19. guard rails as described in one of claim 13-18, is characterized in that: selected plain steel is mild steel, medium carbon steel or high-carbon steel.

The preparation method of 20. guard rails as described in one of claim 13-19, it is characterized in that: described protection gas is argon gas or nitrogen, gas flow is 4-8ml/min.

The preparation method of 21. guard rails as described in one of claim 13-20, is characterized in that: described step 7) in heat treatment step be: heat-treat at 800-550 DEG C, matrix is pearlitic structrure; Or heat-treat at 220-450 DEG C, matrix is bainite structure; Or heat-treat below 220 DEG C, matrix is martensitic structure.