CN103334052A - High-thermal conductivity high-abrasion resistance hot stamping die steel and preparation method thereof - Google Patents

Abstract

The invention relates to a novel high thermal conductivity and high wear resistance hot stamping die material. At present, the steels for hot stamping dies on the market are mainly high-alloy hot work die steels such as various improved H13 and H11. The composition of the steel of the present invention is calculated by mass percentage: C: 0.45-0.5%; Si: <0.2%; Mn: <0.20%; W: 1.0-2.0%; Mo: 2.0-3.5%; Cr: <0.30 %; the rest is Fe and unavoidable impurity elements, S: ≤0.03% in impurity elements; P: ≤0.03. Its characteristics are that simple C, Mo and W elements are the main elements, and the proportion of carbides is coordinated; the content of Mn, low Cr and ultra-low Si is maintained; the material is smelted in an electric furnace → electroslag remelting → annealing → high temperature After homogenization→forging→annealing, it has good machinability; after heat treatment (1060℃~1100℃quenching→multiple high-temperature tempering), it has the toughness and hardness of general hot stamping die steel such as H13 steel in performance. , Tempering stability and thermal fatigue performance are better; especially the lower thermal expansion coefficient, high thermal conductivity and high wear resistance make it more suitable for hot stamping.

Description

Steel for hot stamping die with high thermal conductivity and high wear resistance and preparation method thereof

technical field

The present invention relates to a steel with high thermal conductivity and high wear resistance for hot stamping dies and a preparation method thereof.

Background technique

With the rapid development of the automobile industry and the demand for lightweight automobiles, the demand for ultra-high-strength stamping parts is increasing. The cold stamping forming process requires a lot of pressure to obtain ultra-high-strength steel, which easily reduces the service life of the mold, and is also prone to problems such as cracking, wrinkling, and poor dimensional accuracy. The hot stamping forming process utilizes the plasticity and ductility of the metal at high temperature to increase and the yield strength to decrease, so it is widely used.

The steel plate hot stamping process is to heat a special high-strength steel plate to the austenitic temperature range, quickly move to the mold, and quickly stamp it. The parts are quenched and cooled through the mold equipped with a cooling circuit under the pressure of the press, and finally super High-strength stampings. When working, because the mold is in direct contact with the heated blank, when the hot metal is put into the cavity of the hot stamping mold, the surface of the cavity heats up sharply, and the surface layer generates compressive stress and strain during stamping and holding pressure, which makes the mold need Good thermal strength and thermal stability; but also to withstand strong plastic friction and wear, the mold also needs high wear resistance; in the process of holding pressure, the parts are quenched through the mold with cooling channels, in order to make The mold can quickly take away the heat of the steel plate and ensure the accuracy of the mold during service. The mold material must have a large thermal conductivity and a small thermal expansion coefficient; Affected by tensile stress and tensile strain, the die is prone to thermal fatigue under such alternating temperature conditions; and the hot stamping die steel is also subject to a large impact load during service, so the die must have excellent toughness . In order to prevent the roughening of the mold surface during service, the mold needs to have a higher hardness. Therefore, complex working conditions require hot stamping die materials to have high thermal conductivity, wear resistance, thermal strength, hardness, impact toughness, hardenability, thermal stability, and thermal fatigue resistance.

At present, the hot stamping die steel used in my country is the national standard GB/T1299-2000, the steel number is 4Cr5MoSiV1 (equivalent to North American standard H13 steel). The chemical composition of this hot stamping die steel adopts C 0.32-0.45wt%, Cr 4.75-5.50wt%, Mo 1.20-1.75wt%, V 0.80-1.20wt%, Si 0.80-1.2wt%, Mn 0.20-0.5wt% %, P≤0.03wt%, S≤0.03wt%. At present, Japanese companies use SKD61 hot work die steel (equivalent to North American standard H13 steel), Swedish hot stamping die suppliers use ORVAR, and German companies use CR7V and 1.2379. Theoretically, the thermal conductivity of ferrite in the structure of steel is the highest, about 71~80W/m K, the thermal conductivity of tempered martensite is 35W/m K, and the thermal conductivity of cementite is the lowest. 7W/m·K. The existing H13 hot stamping die steel is a medium-carbon medium-alloy steel, and the proportion of ferrite in the obtained tempered martensite is not high. From the perspective of heat conduction mechanism, for pure metals, heat conduction through free electron movement is the main mechanism. For free electron heat conduction, the resistance of heat conduction is mainly the scattering effect of lattice vibration phonons on free electrons. As the temperature increases, the lattice vibration intensifies, and the resistance of phonons to the movement of free electrons increases, resulting in a decrease in its thermal conductivity. Existing H13 steel contains many kinds of alloying elements, the existence of alloying elements leads to the distortion of the atomic iron lattice and reduces the thermal conductivity; especially the high Si element is contained in the chemical composition, and the difference between the outer electronic structure of Si and Fe Larger, will seriously reduce the thermal conductivity of steel. The wear resistance of H13 steel is mainly related to the content of Mo, V and C in the steel, but the hardness of H13 steel after quenching and tempering is 45-49HRC. When the working temperature is about 500°C, the wear resistance of the mold is not enough, and the service life Short, and the surface quality of the formed material is poor. the

Analysis of Chinese and foreign patent retrieval content for related technologies

By entering keywords related to the content of the present invention to search Chinese and foreign patents, it is found that the patent number related to the hot work die steel and its metallurgical manufacturing technology associated with this patent is

(1) Patent application number: 201110007324.4, name: new heat-resistant and wear-resistant alloy steel material for hot stamping dies, its chemical composition weight percentage content is: C=0.40~0.50, Si=0.3~0.5; Mn=0.65~0.85; P<0.025; S<0.005; Cr2.5~2.7; Mo=2.1~2.4; V=0.8~1.0; the rest are Fe and trace impurities.

(2) Patent application number: 200810046104.0, name: a new type of chromium-based hot work die steel and its heat treatment process, its chemical composition weight percentage content is: carbon C 0.35-0.7%, silicon Si 0.3-1.3%, manganese Mn 0.3 ～1.3%, chromium Cr 7.0～11.0%, tungsten W 0.4～1.2%, molybdenum Mo 0.4～1.2%, vanadium V 0.4～1.2%, nickel Ni 1.0%, sulfur S≤0.005%, phosphorus P≤0.030%, boron B 0.03%-0.10%, the range of nitride content is 0.02% ≤ nitride ≤ 0.20%, 0.02% ≤ nitrogen N ≤ 0.10%, and the rest is iron Fe.

(3) Patent application number: 201080014370.0, name: hot working tool steel with excellent toughness and thermal conductivity, its chemical composition weight percentage content is: C=0.2-1.2%; N=0-1%; B=0 -1%; Cr<1.5%; Ni=1.0-9; Si<0.4; Mn=0-3%; Al=0-2.5%; Mo=0-10%; W=0-15%; Ti=0 -3%; Ta=0-3%; Zr=0-3%; Hf=0-3%; V=0-4%; Nb=0-3%; Cu=0-4%; Co=0- 6%; S=0-1%; Se=0-1%; Te=0-1%; Bi=0-1%; As=0-1%; Sb=0-1%; Ca=0-1 %; the balance is composed of iron and unavoidable impurities, where %Ceq=%C+0.86*%N+1.2*%B, characterized by %Mo+1/2*%W>1.2.

(4) Patent application number: 200710170723.6, name: a hot work die steel with good thermal strength and high toughness, its chemical composition weight percentage content is: C 0.28～0.35, Si 0.20～0.50, Mn 0.20～0.80, Cr 4.50～5.50, Mo 2.00～2.80, V 0.4～0.80, P≤0.025, S≤0.025, Nb 0.05～0.20, N 0.01～0.03, the balance is Fe and unavoidable impurity elements.

The comparative analysis is as follows: From the comparison of the components, it can be seen that the element content of the chemical composition of the present invention is obviously different from that of patents 1-4, the mechanism of the element's effect on the performance of the material is also different, and the application environment of the material is also different.

(1) The similarity between the patent application 201110007324.4 and this patent is that in order to obtain heat-resistant and wear-resistant hot stamping die steel, the content of Si and Mn is lower, the content of Cr is controlled, and W and Mo are added. The two patents The principle of alloying adds V; adding V can refine the grains, and the formed VC improves wear resistance. The present invention controls lower Si, Mn, and Cr by comparison, mainly obtains more ferrite matrix through low alloying, thereby obtains more thermal conductivity, increases Mo content, and can also improve wear resistance sex. The effect of adding W is to make the steel obtain better high temperature strength and tempering stability.

(2) Patent 200810046104.0 increases the chromium content to 7~11%, which can improve the tempering temperature and corrosion resistance. But when the steel contains chromium and molybdenum, when Cr>3%, chromium will delay the coherent precipitation of Mo2C, and Mo2C is a strengthening phase that improves the high temperature strength and tempering resistance of steel. And the addition of alloying element Cr will reduce the thermal conductivity of steel. In contrast, the chemical composition of the present invention controls the Cr content below 0.3%, basically does not use Cr element, so that the hot stamping die steel manufactured by the present invention has better thermal conductivity, high temperature strength and tempering resistance. Patent 200810046104.0 differs from the present invention in that 1% nickel is added. Compared with the present invention, it has the feature of refining grains and increasing toughness by adding nickel to the steel. However, the present invention can obtain a finer structure without adding Ni. The only similarity between the chemical composition of the patent 200810046104.0 and the present invention is the addition of Mo, V and W elements, but the addition of Mo and W in the present invention is more finer than that of the patent 200810046104.0 High, which makes a large amount of tungsten and molybdenum carbides formed in the structure of the material to strengthen the structure, and the content of V is very close, mainly to form VC to increase wear resistance. The chemical composition of the present invention compared with it does not add nickel element, controls lower silicon, manganese, chromium element content, and reduces carbon content, increases Mo and W content, and its strengthening effect to performance is mainly through low Alloying (low silicon, low manganese and chromium), low carbon to obtain more ferrite matrix, thereby obtaining higher thermal conductivity, and the composite effect of multiple carbides of molybdenum and tungsten to obtain better high temperature strength and resilience of steel fire stability etc.

(3) The similarity between patent 201080014370.0 and the present invention is to obtain high thermal conductivity tool steel. The present invention adopts the control of lower C, Si, Mn, Cr elements, and adds W, V, and Mo, but the patent 201080014370.0 adds Ni, Nb, N, and B; Ni is beneficial to improve hardenability, and Nb can refine grains, The addition of B and N is beneficial to obtain high thermal conductivity. In order to coordinate the ratio of Mo, V and W to form carbides, the C content is controlled at 0.45~0.5 to obtain higher thermal conductivity. The role of adding Mo and V is to improve wear resistance, and adding W is to strengthen and improve tempering stability and thermal fatigue ability.

(4) The similarity between patent 200710170723.6 and the present invention is that the added Mo content is roughly the same, mainly for the precipitation of Mo2C in the martensite during tempering, so that the steel has a secondary hardening effect. However, patent 200710170723.6 has higher contents of Si, Mn, and Cr than the present invention, and Nb and N are added. V is added to refine grains, and the carbide obtained by Nb enhances the temper softening resistance of the material. In the present invention, the main purpose of increasing the V content is to obtain carbides to improve wear resistance and refine grains; the main purpose of adding W is to improve thermal stability. C is added to coordinate the formation of carbides and improve the wear resistance and high temperature stability of the material. Cr is reduced in order to obtain higher thermal conductivity.

Contents of the invention

Aiming at the defects existing in the prior art, the object of the present invention is a steel for hot stamping die with high thermal conductivity and high wear resistance and its preparation method. Its purpose is to use a simple chemical composition ratio to coordinate the ratio of C, W, V, and Mo to form carbides. Quenching at 1080°C is used to fully dissolve the alloying elements to achieve the purpose of improving the key performance indicators of the material such as thermal conductivity, wear resistance, hardness, impact toughness and tempering resistance stability. From the perspective of saving economic costs, C, Mo, W, and V are used as the main alloying elements to maintain low Mn, low Cr, and ultra-low Si content, and fully reduce the influence of Si and other elements on thermal conductivity. , so that the patented steel has high thermal conductivity. The main addition of Mo, V, and W elements makes a large amount of complex carbides of W, V, and Mo formed in the structure of the material to achieve a strengthening effect. The carbides of these three elements can increase the strength of the steel and ensure its strength. Toughness, and can make steel obtain good tempering stability, red hardness, hot strength, especially W, V can form special carbides to increase the wear resistance of steel. Therefore, a low-cost and economical hot stamping die steel with high thermal conductivity, high hardness, high wear resistance, good stability against tempering and good impact toughness has been developed.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A steel for hot stamping dies with ultra-high thermal conductivity, the alloy composition of which is mainly composed of the following elements (by mass percentage):

C: 0.45-0.50%;

Si: <0.2%;

Mn: <0.20%;

W: 1.0-2.0%;

Mo: 2.5-3.5%;

Cr: <0.30%;

V: 0.5-1.0%

The rest is Fe and unavoidable impurity elements, S: ≤0.03% in impurity elements; P: ≤0.03.

The following are the effects of the main chemical elements of the present invention:

C 0.45~0.5%

Carbon is mainly present in the form of carbides. When carbon exists in the form of the second phase, the damage to the thermal conductivity of steel is smaller than when it is dissolved in the matrix. It can make strong carbides and manganese weak carbides enter carbides from the matrix, thereby improving thermal conductivity. Therefore, this The patent coordinates the composition ratio of carbon, tungsten, vanadium, and molybdenum, so that they all form carbides without excessive carbon content; at the same time, carbon is one of the main chemical elements of high thermal strength hot work die steel, and part of carbon enters The matrix plays the role of solid solution strengthening, and the other part is to form carbides. The strong carbides formed by molybdenum and tungsten can be finely dispersed and precipitated during high temperature tempering to produce secondary hardening. The carbides formed by vanadium and tungsten can effectively increase abrasion resistance. The carbon content of this design is lower than that of the original material 4Cr5MoSiV1. The purpose is to obtain as much ferrite matrix as possible, thereby improving thermal conductivity and toughness, and improving the distribution and properties of carbides in the steel microstructure. , Improve the level and distribution of liquid carbides in steel. Therefore, if the carbon content is higher than the upper limit of the composition design, it will lead to the formation of excessive carbides and segregation of the structure, which will affect the impact toughness of the steel, especially the inhomogeneity of the liquid carbides in the steel is serious, making the steel The impact toughness is reduced; but the carbon element is lower than the design range of this composition, which will also cause the deviation of the equivalent of carbon and other alloying elements to form carbides, and cannot effectively form stable molybdenum carbides, tungsten carbides and various types. The composite action of carbides affects the hardness, impact toughness and high temperature properties of steel.

Si <0.2%

The electronic structure of the outer layer of silicon is quite different from that of Fe. Studies have shown that it will seriously reduce the thermal conductivity of steel. Therefore, the content of silicon in this design is controlled below 2%. Reducing the silicon content can make the macrostructure more uniform, and can reduce the overcooling of the components on the solidification interface during solidification, and increase the plasticity and toughness. The solid solution strengthening effect of Si is remarkable, no carbide is formed, and it is also insoluble in other carbides. In addition to improving the hardenability of steel, Si also helps to improve the dispersion of special carbides precipitated during high temperature tempering, which can make The secondary hardening peak increases, so Si is an effective element to increase the strength of the matrix and improve the tempering resistance. The role of silicon is to slow down the decomposition of martensite during the tempering process of the steel, and it can be transformed from austenite to martensite. The tempering process after the transformation of tensite effectively hinders the decomposition of martensite, which is mainly by inhibiting the growth of ε carbide points and expanding the stable area of ε carbide, delaying the transformation from ε-carbide to θ-carbide . Silicon delays the transformation of ε→θ, and can fully reduce the growth rate of cementite in steel during tempering. Silicon atoms precipitate from the θ phase and form a silicon atom-enriched region around the θ phase, inhibiting the growth of the θ phase. Growth and coarsening; in addition, silicon can effectively improve the temper softening resistance of steel.

However, when the amount of silicon is too high, the decarburization sensitivity of steel will be aggravated, and the overaging speed of carbide accumulation will increase, making it difficult to control. In addition, silicon and manganese work together to improve the high temperature performance of steel, such as high temperature temper softening resistance and thermal fatigue performance, which are beneficial to the service performance and life of hot work die steel. Based on the above points, this patent adds a small amount of Si.

Mn＜0.20%

In the steelmaking process, manganese can reduce hot brittleness and is a good deoxidizer and desulfurizer. It has a greater affinity with S and can avoid the formation of sulfide FeS with a low melting point on the grain boundary, and the existence of MnS with a certain plasticity with a higher melting point can prevent the thermal embrittlement caused by FeS and eliminate The harmful effects of sulfur improve the hot workability of steel. Dissolving manganese into austenite can improve the hardenability of steel. Mn has a solid solution strengthening effect, thereby increasing the strength and hardness of ferrite and austenite. Although its solid solution strengthening effect is not as good as that of carbon, phosphorus and silicon, it has almost no effect on the ductility of steel.

Although manganese is a weak carbide forming element and cannot form carbide strengthening, the addition of a certain amount of manganese can promote the decomposition of cementite and delay the precipitation and growth of carbides, which is beneficial to the thermal stability of steel . In addition, manganese can increase and stabilize the content of retained austenite in steel, which can improve the toughness and thermal fatigue resistance of steel.

However, if the manganese content is too high, it will promote the segregation of harmful elements, increase the brittleness, weaken the corrosion resistance of steel, reduce the thermal conductivity, welding performance, etc., and comprehensively consider its content to be controlled below 0.2%.

Cr ＜0.30%

Although chromium can be dissolved in ferrite, it can also form carbides. And most of the existing hot work die steels are added with chromium element. The types of chromium carbides are Cr7C3 and Cr23C6 carbides to strengthen the matrix, and the control of this chromium element makes the steel precipitate stable dispersion Phase, this kind of dispersed phase M7C3 and Cr23C6 can not only improve the tempering resistance of the steel, but also make the steel have a certain red hardness and improve the thermal strength of the steel. However, considering that when the tempering temperature is higher than 600 °C, the carbides of Cr will quickly aggregate and coarsen, making the steel's resistance to tempering stability poor, and in terms of thermal conductivity, the increase in Cr content is more important than the increase in W and Mo. The thermal conductivity of steel has a great influence on damage. Therefore, this design controls the chromium content in the range of <0.30%, and mainly uses the carbides of W and Mo to replace the chromium carbides, which can not only achieve the same effect, but also reduce the influence of Cr on thermal conductivity and Reduced steel alloy costs.

Mo: 2.5-3.5%

Molybdenum improves hardenability and heat strength, reduces temper brittleness, increases temper stability, and refines grains. Improves redness in tool steels. Molybdenum element is a strong carbide forming element, and it is also one of the important chemical elements in the composition design of this design. The addition amount of molybdenum element in this design is in the range of 2.5-3.5%. Because the solid solution temperature of molybdenum is not high, it can be dissolved in a large amount during low temperature quenching, and in the form of M2C in the process of tempering, it forms parallel thin needles (two-dimensional Lamellar) precipitates, maintains coherence with the matrix, and improves the high-temperature hardness of the steel. Therefore, by increasing the Mo content in the steel, while increasing the recovery and recrystallization temperature of tempered martensite, Mo can form relatively fine carbides in the steel, thereby further improving the thermal strength and thermal stability of the material. The addition of molybdenum element improves the stability of the steel austenite and the hardenability of the steel, and combines with the carbon element during the tempering process of the steel to form a larger amount of more stable M2C alloy carbide precipitation. The process is the precipitation of a dispersed particle strengthening phase, which is more uniformly distributed in the steel matrix and has a better secondary hardening effect. The control of the amount of molybdenum added in this range makes the steel obtain more M2C alloy carbides in the process of tempering, and produces a larger secondary strengthening effect, which plays an important role in improving the hardness and impact toughness of the steel role. In addition, the addition of tungsten in this patent makes molybdenum and tungsten form a variety of complex carbides, which not only increases the strength of the steel, but also increases the tempering stability and thermal strength of the steel.

W: 1. 0~2.0%

The role of tungsten is mainly to increase the tempering stability, red hardness, heat strength and form special carbides to increase the wear resistance of steel. The addition of molybdenum and tungsten elements in this patent makes a large amount of molybdenum and tungsten formed in the structure of the material. Tungsten carbides strengthen the structure and contribute to improving thermal conductivity.

V: 0.5%-1.0%

Vanadium element is a strong carbide forming element. Its strengthening effect in steel is similar to that of tungsten element. It can improve wear resistance, and at the same time it can hinder the growth of grains and play a role in refining grains. In order to obtain high wear resistance and coordinate the proportion of carbides, V is controlled at 0.5%-1.0%.

P ≤0.03%

In general, phosphorus is a harmful element in steel, which increases the brittleness of steel and reduces the impact toughness of steel. Therefore, the control of phosphorus element is a strict smelting requirement of steel in this technology, which has a certain impact on the performance index value of steel.

S ≤0.03%

Sulfur exists in steel mainly in the form of sulfides. It is generally believed that sulfur is one of the harmful elements in steel. Sulfur is easy to segregate in steel and deteriorates the quality of steel. If it exists in the form of FeS with a lower melting point, it will cause hot embrittlement of steel. To a certain extent, sulfur element is easy to cause the deterioration of the processing performance of steel, and it is easy to cause overheating and overburning of steel in the process of hot working. Therefore, controlling the sulfur content can ensure the processing performance and mechanical properties of the steel, especially to prevent the overheating phenomenon caused by the continuous forging process when the radial forging machine is forging the billet. And play a certain role in improving the microstructure of hot work die steel.

A method for preparing steel for an ultra-high thermal conductivity hot stamping die, which is used to prepare the above-mentioned steel for an ultra-high thermal conductivity hot stamping die. The method adopts the following steps:

(a) Melting: After the alloy is designed according to the above composition, it is smelted according to the traditional method. The batch material in the above formula is placed in the electric furnace and smelted at a temperature above 1500°C; then the steel ingot is poured and enters the next step to be use;

(b) Electroslag remelting: The electroslag remelting process is a voltage of 50V, a current of 2800A, a melting speed of 11mm/min, a depth of molten pool of 50mm, and an electroslag ingot specification of Φ120. After electroslag remelting, the content of gas and inclusions can be reduced, and a steel ingot with uniform composition, compact structure and high quality can be obtained;

(c) Annealing: keep warm at 700℃～900℃ for 8 hours and then cool with the furnace;

(d) Homogenization at high temperature: Heating the above-mentioned steel ingot to 1235-1250°C and keeping it warm for 8-10 hours to homogenize the steel composition, prevent composition segregation, improve the solidification structure of the material, and then place it in the air to cool;

(e) Forging: heat the steel ingot to 1200-1230°C for multi-directional forging, the final forging temperature is 900°C-950°C, the forging ratio should be greater than 6; post-forging annealing: anneal at 800°C-860°C for 8 hours, then cool with the furnace ;

(f) Annealing: Put the above-mentioned steel forging blank into a heating furnace, heat it to 660-700°C, keep it warm for 20-26h, then cool it to 200°C in the furnace, and then air-cool it to room temperature;

Heat treatment process: Quenching at 1060°C to 1100°C, tempering at 560°C to 640°C for 3 times, each tempering for 2 hours; in order to obtain higher thermal conductivity, more alloying elements must be dissolved into the matrix, so the quenching temperature is set at At least 1060°C.

Above; Finally, a new type of high thermal conductivity hot stamping die material is obtained.

Compared with the prior art, the present invention has the following outstanding advantages:

The invention relates to a new type of high thermal conductivity and high wear resistance hot stamping die material. In terms of alloying ideas, the steel of the invention is characterized by simple alloying, mainly composed of four elements: C, Mo, V and W; secondly , keep low Mn, ultra-low Si, Cr elements, so that the patented steel has high thermal conductivity and wear resistance; this can also save economic costs. The properties of the steel of the present invention are: after quenching at 1080°C, the hardness is 54.9HRC; after tempering at 200°C for 2 hours, the hardness is 55.5HRC; after tempering at 300°C for 2 hours, the hardness is 55.1HRC; after tempering at 400°C for 2 hours, the hardness is 53.9HRC; After tempering at 500°C for 2 hours, the hardness is 54.7HRC; after tempering at 520°C for 2 hours, the hardness is 54HRC; after tempering at 540°C for 2 hours, the hardness is 55.9HRC; after tempering at 560°C for 2 hours, the hardness is 55.5HRC; after tempering at 580°C, the hardness is 56.9 HRC; after tempering at 600°C for 2 hours, the hardness is 57.9; after tempering at 620°C for 2 hours, the hardness is 56.7; after tempering at 640°C for 2 hours, the hardness is 51.8HRC. Has excellent temper stability. After quenching at 1080°C + tempering at 560°C for 2 hours + tempering at 580°C for 2 hours + tempering at 600°C for 2 hours, the hardness can reach 56HRC, which is nearly 8 HRC higher than H13, which can improve the wear resistance of the mold and effectively prevent Brushing on the surface of the mold; quenching at a high temperature of 1080°C, so that the alloying elements can be fully dissolved into the matrix, with ultra-high thermal conductivity, see Table 1, the thermal conductivity is compared with that of the existing H13 steel at 700°C It is nearly 31% higher, 53% higher at 400°C, and nearly twice that of H13 at 200°C, which can greatly speed up the stamping cycle and increase production efficiency; the wear resistance is greatly improved compared with H13 steel .

Table 1 Thermal conductivity of imported H13, domestic H13 and invented steel at different temperatures (W/(m*k))

temperature 100 200 300 400 500 600 700 H13 22.24 23.72 24.49 25.4 25.56 27.36 25.44 invention steel 44.56 43 40.33 38.76 35.53 36.3 33.2

The steel of the present invention has good machinability after electric furnace smelting → electroslag remelting → annealing → high temperature homogenization → forging → annealing; after heat treatment (quenching + high temperature tempering), the steel of the present invention has good hot hardness, And has a high thermal conductivity, with high wear resistance.

Description of drawings

Fig. 1 is the comparison of the thermal conductivity of common H13 hot work die steel and steel of the present invention under each temperature of embodiment 1;

Fig. 2 is the microstructure of the quenched state of high thermal conductivity and high wear resistance hot stamping die steel of embodiment 2;

Fig. 3 is the microstructure of the tempered state of high thermal conductivity and high wear resistance hot stamping die steel of embodiment 2;

Fig. 4 is the observation and energy spectrum analysis of W, V and Mo carbides under the SEM electron microscope of the tempered structure of Example 3.

Figure 5 shows the energy spectrum elemental analysis of point 17 in Figure 4.

Fig. 6 is a scanning electron micrograph of the tempered state of high thermal conductivity hot stamping die steel HDCM3 in Example 3.

Detailed ways

The specific embodiment of the present invention is described below in conjunction with accompanying drawing now.

Example 1

Present embodiment has produced a kind of steel, and its concrete composition is as follows:

C: 0.45%;

Si: 0.15%;

Mn: 0.12%;

W: 2.55%;

Mo: 2.6%;

Cr: 0.18%;

V: 0.67%;

The rest is Fe and unavoidable impurity elements, S: ≤0.03% in impurity elements; P: ≤0.03%;

The preparation process and heat treatment process are as follows:

(a) Melting: After the alloy is designed according to the above composition, it is smelted according to the traditional method, the batch material in the above formula is placed in the electric furnace, and smelted at a temperature of 1530°C; then the steel ingot is poured, and the next step is ready for use ;

(b) Electroslag remelting: voltage 50V, current 2800A, melting speed 11mm/min, molten pool depth 50mm, electroslag ingot specification Φ120. After electroslag remelting, the content of gas and inclusions can be reduced, and a steel ingot with uniform composition, compact structure and high quality can be obtained;

(c) Annealing: heat at 900°C for 8 hours and then cool with the furnace;

(d) Homogenization at high temperature: Heating the steel ingot above to 1250°C and keeping it warm for 10 hours to homogenize the composition of the steel, prevent composition segregation, improve the solidification structure of the material, and then place it in the air to cool;

(e) Forging: heat the steel ingot to 1230°C for multi-directional forging, the final forging temperature is 950°C, and the forging ratio should be greater than 6; Annealing after forging: anneal at 860°C for 8 hours, then cool in the furnace;

(f) Annealing: Put the above-mentioned steel forging blank into a heating furnace, heat it to 700°C, keep it for 25 hours, then cool it to 200°C in the furnace, and then air cool it to room temperature;

(g) Heat treatment process: quenching at 1080°C for 45 minutes, tempering three times at 560-2h+580-2h+600-2h; under the recommended heat treatment process conditions, the hardness value is 57HRC, and the impact toughness value is 110-130J.

(h) Figure 1 shows the thermal conductivity test results. At 200°C, the thermal conductivity is 43 W/(m*K), and at 700°C, the thermal conductivity is 33.2 W/(m*K) . As the temperature increases, the thermal conductivity of the patented steel gradually decreases, but at 700°C, the thermal conductivity is nearly 31% higher than that of the H13 steel.

Example 2

Present embodiment has produced a kind of steel, and its concrete composition is as follows:

C: 0.50%;

Si: 0.08%;

Mn: 0.15%;

W: 1.8%;

Mo: 2.5%;

Cr: 0.08%;

V: 0.8%;

The rest is Fe and unavoidable impurity elements, S: ≤0.05% in impurity elements; P: ≤0.03%;

The preparation process and heat treatment process are as follows:

(a) Melting: After the alloy is designed according to the above composition, it is smelted according to the traditional method, the batch material in the above formula is placed in the electric furnace, and smelted at a temperature above 1500°C; then the steel ingot is poured, and the next step is to be use;

(b) Electroslag remelting: The electroslag remelting process is a voltage of 50V, a current of 2800A, a melting speed of 11mm/min, a depth of molten pool of 50mm, and an electroslag ingot specification of Φ120. After electroslag remelting, the content of gas and inclusions can be reduced, and a steel ingot with uniform composition, compact structure and high quality can be obtained;

(c) Annealing: heat at 800°C for 8 hours and then cool with the furnace;

(d) Homogenization at high temperature: Heating the above-mentioned steel ingot to 1250°C and holding it for 10 hours to homogenize the composition of the steel, prevent composition segregation, improve the solidification structure of the material, and then place it in the air to cool;

(e) Forging: heat the steel ingot to 1230°C for multi-directional forging, the final forging temperature is 950°C, and the forging ratio should be greater than 6; Annealing after forging: anneal at 860°C for 8 hours, then cool with the furnace;

(f) Annealing: Put the above-mentioned steel forging blank into a heating furnace, heat it to 700°C, keep it for 25 hours, then cool it to 200°C in the furnace, and then air cool it to room temperature;

(g) Heat treatment process: quenching at 1080°C for 45 minutes, tempering three times at 560-2h+600-2h+620-2h; under the recommended heat treatment process conditions, the hardness value is 56HRC, and the impact toughness value is 120-150J.

(h) As shown in Figure 1, the thermal conductivity test results are shown. At 200°C, the thermal conductivity is 44.2 W/(m*K), and at 700°C, the thermal conductivity is 34.2 W/(m*K) .

Example 3

Present embodiment has produced a kind of steel, and its concrete composition is as follows:

C: 0.48%;

Si: 0.12%;

Mn: 0.15%;

W: 1.8%;

Mo: 2.7%;

Cr: 0.18%;

V: 0.54%;

The rest is Fe and unavoidable impurity elements, S: ≤0.03% in impurity elements; P: ≤0.03%;

The preparation process and heat treatment process are as follows:

(a) Melting: After the alloy is designed according to the above composition, it is smelted according to the traditional method, the batch material in the above formula is placed in the electric furnace, and smelted at a temperature above 1500°C; then the steel ingot is poured, and the next step is to be use;

(b) Electroslag remelting: The electroslag remelting process is a voltage of 50V, a current of 2800A, a melting speed of 11mm/min, a depth of molten pool of 50mm, and an electroslag ingot specification of Φ120. After electroslag remelting, the content of gas and inclusions can be reduced, and a steel ingot with uniform composition, compact structure and high quality can be obtained;

(c) Annealing: heat at 900°C for 8 hours and then cool with the furnace;

(d) Homogenization at high temperature: heat the above-mentioned steel ingot to 1235°C and keep it warm for 10 hours to homogenize the steel composition, prevent composition segregation, improve the solidification structure of the material, and then place it in the air to cool;

(e) Forging: heat the steel ingot to 1210°C for multi-directional forging, the final forging temperature is 950°C, and the forging ratio should be greater than 6; Annealing after forging: anneal at 860°C for 8 hours, then cool with the furnace;

(f) Annealing: Put the above-mentioned steel forging blank into a heating furnace, heat it to 680°C, keep it for 24 hours, then cool it to 200°C in the furnace, and then air cool it to room temperature;

(g) Heat treatment process: heat preservation at 1080°C for 45 minutes, quenching, 560-2h+600-2h+640-2h and tempering three times; under the recommended heat treatment process conditions, the hardness value is 52HRC, and the impact toughness value is 160-180J.

(h) As shown in Figure 1, the thermal conductivity test results are shown. At 200°C, the thermal conductivity is 42.4W/(m*K), and at 700°C, the thermal conductivity is 32.2 W/(m*K) . the

Claims (3)

1. A steel for hot stamping dies with ultra-high thermal conductivity, characterized in that the alloy composition is mainly composed of the following elements, in terms of mass percentage: C: 0.45-0.50%; Si: <0.2%; Mn <0.2%; W: 1.0-2.0%; Mo: 2.5-3.5%; Cr: <0.2%; V: 0.5-1.0%; the rest is Fe and unavoidable impurity elements. 2. A steel for ultra-high thermal conductivity hot stamping dies according to claim, characterized in that the steel has a tempering hardness of 56-57HRC and a thermal conductivity of 42-44.5W/(m*K at 200°C ), at 700°C it is 32~33.5W/(m*K). 3. A preparation method of steel for ultra-high thermal conductivity hot stamping dies, for preparing the steel for ultra-high thermal conductivity hot stamping dies according to claim, the method adopts the following steps: (a) Melting: According to the composition of steel alloys for hot stamping dies with ultra-high thermal conductivity, in terms of mass percentage: C: 0.45-0.50%; Si: <0.2%; Mn<0.20%; W: 1.0-2.0%; Mo: 2.5-3.5%; Cr: <0.20%; V: 0.5-1%; the rest is Fe and unavoidable impurity elements; smelting is carried out according to the traditional method, and the batch material is placed in the electric furnace, at 1500 Melting at a temperature above ℃; then pouring ingots, the next step is to be used; (b) Electroslag remelting: voltage 50V, current 2800A, melting speed 11mm/min, molten pool depth 50mm, electroslag ingot specification Φ120; after electroslag remelting, the content of gas and inclusions can be reduced, and the composition can be uniform, Steel ingots with dense structure and high quality; (c) Annealing: keep warm at 700℃～900℃ for 8 hours and then cool with the furnace; (d) Homogenization at high temperature: Heating the above-mentioned steel ingot to 1235-1250°C and keeping it warm for 8-10 hours to homogenize the steel composition, prevent composition segregation, improve the solidification structure of the material, and then place it in the air to cool; (e) Forging: heat the steel ingot to 1200-1230°C for multi-directional forging, the final forging temperature is 900°C-950°C, and the forging ratio should be greater than 6; Annealing after forging: anneal at 800°C-860°C for 8 hours, then cool in the furnace ; (f) Annealing: Put the above-mentioned steel forging blank into a heating furnace, heat it to 660-700°C, keep it warm for 20-26h, then cool it to 200°C in the furnace, and then air-cool it to room temperature; (g) Heat treatment process: Quenching at 1060°C to 1100°C, tempering at 560°C to 640°C for 3 times, each tempering for 2 hours; finally a new type of alloy steel material for heat-resistant and wear-resistant hot stamping dies is obtained.

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