CN100526495C - Boron-containing casting die steel and preparation method thereof - Google Patents

Abstract

The invention relates to boracic cast die steel and a preparation method thereof, which belongs to the die technical field. The boracic cast die steel comprises the following chemical compositions in percentage by weight (wt percent): 0.85 to 1.00 percent of C, 6.0 to 8.0 percent of Cr, 0.6 to 1.0 percent of Si, 0.8 to 1.5 percent of Mn, 2.2 to 2.8 percent of B, 0.25 to 0.5 percent of Al, 1.2 to 1.5 percent of Ti, 0.08 to 0.15 percent of N, 0.05 to 0.08 percent of Mg, 0.08 to 0.12 percent of RE, less than 0.04 percent of S, less than 0.04 percent of P, the balance being Fe. In the invention, molten steel is melted and poured and cast to a die, then kept between 950 DEG C and 1000 DEG C for 2h to 5h and treated by oil quenching and drawing temper between 180 DEG C and 250 DEG C for 6h to 8h, thereby making the boracic cast die steel. Compared with the prior art, the boracic cast die steel has the advantages of high intensity and rigidity, good toughness and wear resistance, low cost, etc.

Description

Boron-containing casting die steel and preparation method thereof

technical field

The invention belongs to the technical field of molds, in particular to boron-containing casting mold steel and a preparation method thereof.

Background technique

Mold is an essential tool in the production process of refractory products, and it works on friction brick presses or hydraulic presses ranging from tens to thousands of tons. During the working process, the mold is subjected to the abrasive wear of the hard particles of the refractory material, resulting in a decrease in service life, an increase in production cost, a decrease in production efficiency, and a serious impact on product quality. In recent years, with the development of large-scale and high-density refractory products, high-pressure molding equipment has appeared, which puts forward stricter requirements for molds. Therefore, it is an urgent task for mold workers to choose suitable materials and use advanced production technology to manufacture high-quality molds. For many years, my country's refractory industry has used carbon steel carburizing molds and partially deteriorated cast iron molds. With the development of production technology, the shortcomings of such molds have gradually been exposed. The former has a shallow hardened layer and is easy to deform after carburizing, while the latter is brittle and easy to break during use. In recent years, new materials for forming molds for refractory products have developed rapidly, and the application of high-chromium cast iron, hard alloys, steel-bonded hard alloys and high-alloy mold steels has created favorable conditions for improving the service life of molds.

Chinese invention patent CN87102001 discloses a process of spray welding wear-resistant coating on the surface of a refractory material mold. The coating material is a nickel-based self-fluxing alloy powder containing WC. With the help of a powder spray gun, the powder is heated to melt through the oxyacetylene flame zone Or semi-molten state, sprayed on the surface of the refractory mold, and then remelted by induction heating to obtain a 1-2.5mm thick wear-resistant coating, the coating hardness is 63-67HRC, and the bonding strength with the substrate is greater than 350MPa. Smooth, flat and dense. However, the spray welding wear-resistant coating of the mold is easy to crack and peel off during use, and the mold is prone to deformation during spray welding, which affects the surface quality of refractory products. Chinese invention patent CN1931547 also discloses a refractory brick mold prepared with a wear-resistant alloy composite plate, which is characterized in that low-carbon steel is used as a substrate, and a wear-resistant hard alloy layer with a certain thickness is formed on the substrate by fusion welding. The invention has a simple and reasonable technological process, can produce refractory brick molds with complex shapes, greatly improves its service life, and reduces mold costs. The refractory brick mold made of wear-resistant alloy composite plate has high wear resistance during use, and the wear-resistant alloy layer does not fall off. However, there are deficiencies in the manufacturing of refractory product molds by the invention, such as less grinding times and easy deformation during mold spray welding, which affects the surface quality of refractory products. Chinese invention patent CN1060878 also discloses a brick pressing mold for producing refractory bricks made of high wear-resistant alloy materials and a process method for making molds, which is through alloying and compound modification of high-chromium multi-element alloys, characterized in that The selection of the chemical composition of the alloy material; the formula and process of the compound modification treatment; the heat treatment conditions of the mold. The mold can be assembled, and the mold sleeve is a movable mold sleeve or a fixed mold sleeve with an enlarged inner cavity. The invention has high wear resistance and strong toughness, which improves the quality of refractory bricks. The mold of the invention also has the characteristics of short mold changing time, saving raw materials and energy, and long service life. However, because the mold material contains more chromium elements, expensive alloy elements such as nickel, copper, and tungsten are also added to improve the hardenability and wear resistance of the mold, resulting in an increase in mold production costs.

Contents of the invention

The purpose of the present invention is to solve the problems of the prior art, and provide a chemical composition of boron-containing casting mold steel and a preparation method thereof. Its main feature is to smelt carbon steel in an electric furnace, and add a certain amount of chromium to the steel to improve the hardenability of cast steel, and also add a certain amount of boron to generate high-hardness borides, improve the hardness of cast steel and Improve the wear resistance of cast steel. A certain amount of titanium is also added, mainly to refine the solidification structure, and improve the shape and distribution of borides. An appropriate amount of aluminum is also added to help improve the shape of borides and improve the strength and toughness of cast steel. And add rare earth magnesium alloy and nitrogen to further improve the structure of cast steel and improve the performance of cast steel.

The purpose of the present invention can be achieved through the following technical solutions:

The chemical composition and weight percentage of the boron-containing casting mold steel provided by the present invention are: C: 0.85-1.00%, Cr: 6.0-8.0%, Si: 0.6-1.0%, Mn: 0.8-1.5%, B: 2.2 ～2.8%, Al: 0.25～0.50%, Ti: 1.20～1.50%, N: 0.08～0.15%, Mg: 0.05～0.08%, RE: 0.08～0.12%, S<0.04%, P<0.04%, remainder The amount is Fe.

The boron-containing cast mold steel provided by the present invention is produced in an electric furnace, specifically comprising the following steps:

① Use steel scrap, ferrochrome, pig iron, ferrosilicon, ferromanganese, aluminum, ferrotitanium, ferroboron, rare earth magnesium alloy and nitrogen-containing ferrochrome, according to the weight percentage of the chemical composition in the target product C: 0.85 ~ 1.00%, Cr: 6.0 ～8.0%, Si: 0.6～1.0%, Mn: 0.8～1.5%, B: 2.2～2.8%, Al: 0.25～0.50%, Ti: 1.20～1.50%, N: 0.08～0.15%, Mg: 0.05～ 0.08%, RE: 0.08～0.12%, S<0.04%, P<0.04%, the balance is Fe for material preparation;

②Put scrap steel, ferrochrome and pig iron into the furnace for heating and melting, after molten steel is melted, add ferrosilicon and ferromanganese in sequence;

③ After adjusting the composition before the furnace, the temperature is raised to 1550-1580°C, then aluminum is added for deoxidation and alloying, then ferro-titanium and ferro-boron are added in sequence, and then the temperature of molten steel is raised to 1590-1620°C;

④Crush the rare earth magnesium alloy and nitrogen-containing ferrochromium into small pieces with a particle size of 6-10mm, dry them at 150-180°C, place them at the bottom of the ladle, and compound the molten steel in step ③ by pouring into the ladle deterioration treatment;

⑤ Pouring the molten steel after compound modification treatment into refractory products mold, the pouring temperature of molten steel is 1480～1500℃;

⑥ Heat the mold obtained in step ⑤ at 950-1000°C for 2-5 hours, then oil-cool and quench, and control the quenching oil temperature at 20-80°C;

⑦Tempering the quenched mold at 180-250°C, holding time for 6-8 hours for tempering, furnace cooling or air cooling after tempering, to obtain a boron-containing casting mold.

The performance of cast mold steel is determined by the metallographic structure, and a certain structure depends on the chemical composition and heat treatment process. The chemical composition of the present invention is determined as follows:

Carbon: Carbon is the main element that affects the hardness and toughness of cast mold steel. When the carbon content is high, the matrix hardenability and hardenability are good, the hardness is high, and the wear resistance is good. In addition, when the carbon content is high, the number of carbides in the casting structure More, it is also beneficial to improve the wear resistance of the die steel, but the increase of the carbon content will lead to the increase of the brittleness of the die steel and the enhancement of the quenching cracking tendency, and the carbon content should be controlled at 0.85-1.00%.

Boron: Boron is a special element with an atomic number of 5, which is between metals and nonmetals, and can be combined with metals and nonmetals. Adding a certain amount of boron to cast steel can easily form high-hardness borides and improve the wear resistance of cast steel. Part of boron is dissolved in the matrix, which is beneficial to improve the hardenability of cast steel. If the amount of boron added is too small, the amount of borides is small, and the effect on improving the wear resistance of the die steel is not obvious. If the amount of boron added is too large, the brittle borides will increase significantly, which will damage the strength and toughness of the die steel. Comprehensive consideration should be given to control the boron content at 2.2 ~2.8%.

Chromium: Chromium is added to the die steel. On the one hand, it can be dissolved in the matrix to improve the hardenability of the matrix. On the other hand, it can form carbides to improve the wear resistance of cast steel. Chromium can also be dissolved in borides and reduce borides. The role of brittleness, chromium also promotes the increase of the solid solution of boron in the matrix, which has the effect of indirectly improving the hardenability of cast steel. In addition, chromium can refine grains and improve tempering stability. Too much chromium added will increase the production cost of cast steel, so the chromium content should be controlled at 6.0-8.0% in comprehensive consideration.

Silicon: Silicon is solid-soluble in ferrite and austenite, and has obvious strengthening effect. Silicon can reduce the solubility of carbon in austenite, promote the precipitation of carbides, and increase strength and hardness. The affinity of silicon and oxygen is second only to aluminum and titanium, but stronger than manganese, chromium, vanadium, etc. plasticity and toughness. Considering comprehensively, the silicon content is controlled at 0.6-1.0%.

Manganese: Manganese can strongly increase the hardenability of steel, and it is easy to obtain martensitic structure after quenching. Manganese can also act as a deoxidizer and desulfurizer, and can purify molten steel, but high manganese content will promote coarse grains. Comprehensive consideration, manganese is controlled at 0.8-1.5%.

Rare earth, aluminum, and nitrogen: Adding rare earth, aluminum, and nitrogen to boron-containing cast steel can easily generate REAlO ₃ and AlN to nucleate primary austenite, which is beneficial to promote the refinement of primary austenite. Moreover, the rare earth and aluminum increase the surface tension of molten steel, making borides develop into lumps. Nitrogen also acts as an adsorbent, passivating the surface of the boride particles. The improvement of boride morphology is beneficial to the improvement of cast steel strength and hardness. Excessive addition of rare earth and aluminum will lead to more inclusions, which is not conducive to improving the strength and toughness of cast steel. If the amount of nitrogen added is too much, pores will easily appear in the casting mold, which will damage the mechanical properties and performance of the mold. Comprehensive consideration should be given to controlling the rare earth content at 0.08-0.12%, the nitrogen content at 0.08-0.15%, and the aluminum content at 0.25-0.50 %.

Titanium: Titanium is added to boron-containing cast steel, Ti+2B=TiB ₂ reaction occurs, and massive TiB ₂ is formed, which has a significant effect on improving the form and distribution of iron-boron compounds, and is beneficial to improve the mechanics of boron-containing cast steel performance. If the amount of titanium added is too much, coarse massive TiB ₂ will appear, which will reduce the strength and toughness of the cast steel, so the titanium content should be controlled at 1.20-1.50% comprehensively.

Magnesium: Magnesium is a surface active element, which is selectively adsorbed on the surface of the eutectic boride in the preferred growth direction during eutectic crystallization, forming an adsorption film, which hinders the growth of B, Fe, Cr and other atoms in the molten steel into eutectic boron The compound crystal reduces the growth rate of the preferred direction of the eutectic boride, resulting in a slowdown in the growth of the preferred direction, while the growth rate of other directions increases, which promotes the transformation of the eutectic boride from a network to a broken network and agglomerates .

Phosphorus and sulfur: Unavoidable trace impurities are brought into the raw materials, including phosphorus and sulfur, which are harmful elements. In order to ensure the strength, toughness and wear resistance of boron-containing casting die steel, the phosphorus content is controlled at 0.04% Below, the sulfur content is controlled below 0.04%.

The performance of cast mold steel is also related to the heat treatment process, which is determined in this way in the present invention.

In order to ensure that the cast mold steel obtains the martensitic structure, it is first necessary to heat it to 950-1000°C and keep it warm for 2-5 hours. Reduce tool steel hardness and wear resistance. If the heating temperature is too high or the holding time is too long, the quenched structure will be coarse, which will damage the strength and toughness of the die steel, and the energy consumption will be high and the efficiency will be low. Oil cooling after quenching can ensure that the quenched structure obtains a single martensite matrix. After the mold is quenched, it is tempered at 180-250°C, which can stabilize the structure and eliminate stress. If the tempering temperature is too low or the holding time is too short, the mold stress is large and it is easy to crack during use. If the tempering temperature is too high or the tempering holding time is too long, the hardness of the mold will decrease, and the wear resistance will decrease. Choosing tempering at 180-250°C and holding time for 6-8 hours will have a good effect.

Compared with prior art, the present invention has following advantage:

①The boron-containing casting mold steel of the present invention does not contain expensive alloy elements such as molybdenum, nickel, copper, etc., has low production cost, simple production process, and uses boron as the main alloy element. In addition to obviously improving hardenability, it also produces a large amount of high hardness Borides can significantly improve the wear resistance of molds.

②The boron-containing casting die steel of the present invention has high hardness, and adopts rare earth, aluminum, nitrogen, magnesium, titanium and other elements to refine the solidification structure, improve the form and distribution of borides, and improve the strength and toughness of the boron-containing casting die steel. The tensile strength exceeds 650Mpa, the impact toughness exceeds 12J/cm ² , and the hardness exceeds 65HRC.

③ The boron-containing casting mold steel of the present invention has excellent wear resistance, which is 30-50% higher than that of high-chromium white cast iron, but the production cost is 30-40% lower than that of high-chromium cast iron molds.

Detailed ways

Below in conjunction with embodiment the present invention is described in further detail:

Example 1

Melting boron-containing casting mold steel with a 500 kg medium-frequency induction furnace, the manufacturing process steps are:

① Mix steel scrap, ferrochrome and pig iron into the furnace to heat and melt, and then add ferrosilicon and ferromanganese in turn after molten steel is melted;

② After adjusting the ingredients before the furnace, the temperature is raised to 1572°C, then aluminum is added for deoxidation and alloying, then ferro-titanium and ferro-boron are added in sequence, and the temperature of molten steel is raised to 1618°C;

③Crush the rare earth magnesium alloy and nitrogen-containing ferrochrome into small pieces with a particle size of 6-10mm, dry them at 150-180°C, place them at the bottom of the ladle, and perform compound modification treatment on the molten steel by pouring into the ladle;

④ Pouring molten steel into refractory product molds, the pouring temperature of molten steel is 1493°C;

⑤ After the mold is kept at 980°C for 4 hours, it is oil-cooled and quenched, and the temperature of the quenching oil is controlled at 20-80°C;

⑥ After the mold is quenched, it is tempered at 220°C, the tempering holding time is 7 hours, and the furnace is cooled after tempering. The composition of die steel is shown in Table 1, and the mechanical properties of die steel are shown in Table 2.

element C Cr Si mn B Al Ti content 0.98 6.19 0.97 0.84 2.79 0.48 1.50 element N Mg RE S P Fe content 0.09 0.07 0.09 0.027 0.033 margin

Table 1 Die steel composition and content (weight%)

Tensile strength over Mpa Impact toughness J/cm² Hardness HRC 663.8 12.6 66.4

Table 2 Mechanical properties of die steel

Example 2

Using a 1000 kg medium frequency induction furnace to melt boron-containing casting die steel, the manufacturing process steps are:

① Mix steel scrap, ferrochrome and pig iron into the furnace to heat and melt, and then add ferrosilicon and ferromanganese in turn after molten steel is melted;

② After adjusting the composition before the furnace, the temperature is raised to 1555°C, then aluminum is added for deoxidation and alloying, then ferro-titanium and ferro-boron are added in sequence, and the temperature of molten steel is raised to 1597°C;

③Crush the rare earth magnesium alloy and nitrogen-containing ferrochrome into small pieces with a particle size of 6-10mm, dry them at 150-180°C, place them at the bottom of the ladle, and perform compound modification treatment on the molten steel by pouring into the ladle;

④ Pouring molten steel into refractory product molds, the pouring temperature of molten steel is 1489°C;

⑤ After the mold is kept at 960°C for 5 hours, it is oil-cooled and quenched, and the temperature of the quenching oil is controlled at 20-80°C;

⑥ After the mold is quenched, it is tempered at 250°C, the tempering time is 6 hours, and it is air-cooled after tempering. The composition of die steel is shown in Table 3, and the mechanical properties of die steel are shown in Table 4.

element C Cr Si mn B Al Ti content 0.87 7.80 0.63 1.46 2.28 0.27 1.25 element N Mg RE S P Fe content 0.15 0.05 0.11 0.023 0.038 margin

Table 3 Die steel composition and content (weight%)

Tensile strength over Mpa Impact toughness J/cm² Hardness HRC 672.7 12.9 66.1

Table 4 Mechanical properties of die steel

Example 3

Melting boron-containing casting mold steel with a 750 kg medium frequency induction furnace, the manufacturing process steps are:

① Mix steel scrap, ferrochrome and pig iron into the furnace to heat and melt, and then add ferrosilicon and ferromanganese in turn after molten steel is melted;

② After adjusting the composition before the furnace, the temperature is raised to 1569°C, then aluminum is added for deoxidation and alloying, then ferro-titanium and ferro-boron are added in sequence, and the temperature of molten steel is raised to 1603°C;

③Crush the rare earth magnesium alloy and nitrogen-containing ferrochrome into small pieces with a particle size of 6-10mm, dry them at 150-180°C, place them at the bottom of the ladle, and perform compound modification treatment on the molten steel by pouring into the ladle;

④ Pouring molten steel into refractory product molds, the pouring temperature of molten steel is 1495°C;

⑤ After the mold is kept at 1000°C for 2 hours, it is oil-cooled and quenched, and the temperature of the quenching oil is controlled at 20-80°C;

⑥ After the mold is quenched, it is tempered at 180°C, the tempering holding time is 8 hours, and the furnace is cooled after tempering. The composition of die steel is shown in Table 5, and the mechanical properties of die steel are shown in Table 6.

element C Cr Si mn B Al Ti content 0.91 7.06 0.81 1.27 2.60 0.39 1.41 element N Mg RE S P Fe content 0.10 0.07 0.09 0.027 0.032 margin

Table 5 Die steel composition and content (weight %)

Tensile strength over Mpa Impact toughness J/cm² Hardness HRC 681.4 13.2 65.7

Table 6 Mechanical properties of die steel

The refractory product mold made of the boron-containing casting mold steel of the present invention is used to press and form magnesia bricks on a 300-ton brick press in a refractory factory, and each set of molds can form more than 12,000 pieces each time. The amount of grinding each time is only 0.3-0.4mm, while in the past, only 3,000 pieces were formed each time using carburizing steel molds, and each grinding was 0.7-0.9mm. High chromium cast iron molds are formed about 9,000 pieces each time, and each time the grinding is 0.4-0.5mm. Using the boron-containing cast steel mold provided by the invention has small deformation, less grinding amount, long service life, good surface quality of refractory products, and good economic and social benefits.

Claims (2)

1, a kind of boron-containing casting die steel is characterized in that, the chemical ingredients of boron-containing casting die steel and weight percent thereof are: C:0.85～1.00%, Cr:6.0～8.0%, Si:0.6～1.0%, Mn:0.8～1.5%, B:2.2～2.8%, Al:0.25～0.50%, Ti:1.20～1.50%, N:0.08～0.15%, Mg:0.05～0.08%, RE:0.08～0.12%, S＜0.04%, P＜0.04%, surplus are Fe.

2, the preparation method of a kind of boron-containing casting die steel according to claim 1 is characterized in that, may further comprise the steps:

1. with steel scrap, ferrochrome, the pig iron, ferrosilicon, ferromanganese, aluminium, ferrotianium, ferro-boron, magnesium-rare earth with contain nitrogenous ferrochrome, according to target chemical component weight per-cent is got the raw materials ready in the product, C:0.85～1.00%, Cr:6.0～8.0%, Si:0.6～1.0%, Mn:0.8～1.5%, B:2.2～2.8%, Al:0.25～0.50%, Ti:1.20～1.50%, N:0.08～0.15%, Mg:0.05～0.08%, RE:0.08～0.12%, S＜0.04%, P＜0.04%, surplus are Fe;

2. put into the electric furnace heat fused after steel scrap, ferrochrome and the pig iron being mixed, molten steel adds ferrosilicon and ferromanganese after melting clearly successively;

3. the stokehold is adjusted to branch and temperature is risen to 1550～1580 ℃ after qualified, adds aluminium deoxidation and alloying then, adds ferrotianium and ferro-boron more successively, liquid steel temperature is risen to 1590～1620 ℃ then;

4. with magnesium-rare earth with contain nitrogenous ferrochrome and be crushed to the fritter that granularity is 6～10mm, after 150～180 ℃ of oven dry, place the casting ladle bottom, the molten steel of step in 3. carried out the composite inoculating processing with pouring method in the bag;

5. the pouring molten steel after composite inoculating being handled becomes refractory product mould, and the pouring molten steel temperature is 1480～1500 ℃;

6. the mould that 5. step is obtained is 950～1000 ℃ of insulation oil quenchinngs after 2～5 hours, and the quenching oil temperature is controlled at 20～80 ℃;

7. the mould after will quenching carries out temper at 180～250 ℃, tempering insulation time 6～8 hours, and the cold or air cooling of stove makes boron-containing casting die after the tempering.