CN100510148C - High heat-intensity hot-work die steel material - Google Patents

Abstract

The invention relates to a hot work die steel material, which belongs to the technical field of alloy steel material manufacturing technology. The high thermal strength hot work die steel material of the present invention is characterized in that it has the following composition and weight percentage: Cr 3.5-4.0%, Mo 2.0-2.5%, V 1.0-1.5%, W 1.0-1.5%, Mn 0.1- 0.5, Ni 0.1~0.25%, C 0.3~0.35%, Si 0.1~0.5%, S 0.005~0.01%, P 0.01~0.02, Fe balance. The preparation process of the alloy steel is as follows: (1) melting, (2) electroslag remelting, (3) high temperature homogenization, (4) forging, (5) forging annealing, (6) blank forging, (7) annealing; Finally, the product hot work die steel is obtained. The mold steel has a relatively high service hardness, and the hardness is in the range of 48-54HRC; the room temperature impact toughness value of the material is greater than 300J, and has better thermal fatigue performance.

Description

High thermal strength hot work die steel material

technical field

The invention relates to a hot work die steel material, which belongs to the technical field of alloy steel material manufacturing technology.

Background technique

Hot work die steel generally operates under quite complex working conditions, and the performance requirements for die steel materials are also quite strict. When working, the material bears a great impact force. After the mold cavity is in contact with the high-temperature metal, the temperature itself often reaches 300-400°C, and the local temperature can reach 500-700°C, and some even reach about 1000°C. Heating and cooling. In the state of sometimes cold and sometimes hot, it is easy to cause thermal fatigue cracks on the working surface of the mold, that is, cracks; when the hot metal is forced to deform, it will rub against the surface of the mold cavity, and the mold is easily worn and its hardness is reduced; the mold is at high temperature. Mechanical stress cycles can also lead to plastic deformation and crack initiation. In addition, when the mold is used at a higher temperature, there will be a phenomenon of softness, that is, with the increase of the number of uses, the hardness of the mold will decrease, so that it cannot meet the performance requirements. Some materials will also be scrapped due to cracking due to insufficient high temperature toughness or insufficient cold and heat fatigue resistance. Therefore, how to make die steel have durable high-temperature strength and toughness is a research topic that researchers pay attention to.

The well-known H13 steel is a hot work die steel with excellent comprehensive properties. In general, H13 steel is often used as hot extrusion dies, aluminum alloy die-casting dies and plastic dies, but its service temperature should not exceed 600°C. It can also be used as cold extrusion die, cold extrusion steel pipe ring die, top piece, etc. It is a die steel that can be used for both cold and heat. When the working temperature is higher than 600°C, such as some steel or copper hot extrusion dies and copper alloy die-casting dies, the surface heating temperature can reach 700°C or even higher. At this time, H13 steel loses its original excellent performance. Although 3Cr2W8V alloy steel also has good thermal hardness, its thermal fatigue resistance is poor, and the mold often fails early due to cracks, which seriously limits its service life.

In view of this, many scientific researchers at home and abroad are committed to the research of new high-heat-strength hot-work die steels. Although many new steel types have been developed, and there are many steel types with excellent performance, most of them are aimed at A certain aspect of the problem was born, and the application field has certain limitations. Therefore, there is still a long way to go in the research of high thermal strength hot work die steel. People expect to obtain new hot work die steel materials with higher comprehensive performance and wider application range.

Contents of the invention

The object of the present invention is to provide a high thermal strength hot work die steel material and a preparation method thereof.

A high thermal strength hot work die steel material of the present invention is characterized in that it has the following composition and weight percentage: Cr 3.5-4.0%

Mo 2.0～2.5%

V 1.0～1.5%

W 1.0～1.5%

Mn 0.1～0.5%

Ni 0.1～0.25%

C 0.3～0.35%

Si 0.1～0.5%

S 0.005～0.01%

P 0.01～0.02%

Fe balance

A kind of preparation method of high thermal strength hot work die steel of the present invention is characterized in that having following technological process and steps:

(a) Melting: smelting according to the traditional conventional method, placing the batch material according to the above formula in an intermediate frequency induction furnace, and smelting at a temperature above 1500°C; then pouring steel ingots, and entering the next step for use;

(b) Electroslag remelting: using electric current to generate resistance heat through the electroslag layer to melt the alloy base material of the consumable electrode, the liquid metal falls in the form of molten droplets through the slag layer into the metal molten pool in the water-cooled crystallizer, and the steel ingot is formed by Gradually crystallize from bottom to top. 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. The alloy is further refined during remelting, and inclusions are removed by slag washing and floating in the molten pool. The durability and plasticity of the alloy are improved, and various macroscopic and microscopic defects are eliminated or alleviated;

(c) Homogenization at high temperature: then heating to a temperature of 1200-1240°C, and keeping it warm for 8-10 hours to homogenize the steel components, and then burying sand to cool;

(d) Forging: heating the above steel ingot to 1200-1230°C for rough forging, the final forging temperature is 940°C to obtain a forging;

(e) Annealing of forgings: annealing at 830°C for 8 hours, then cooling in the furnace;

(f) Blank forging: reheat to 1100-1300°C, and perform forging again in the temperature range of 930-1100°C:

(g) Annealing: at 810°C, it is annealed again for 7 hours, then cooled in the furnace, and finally the product hot work die steel is obtained.

The theoretical basis of the hot work die steel design composition formula of the present invention is as follows:

(1) Obtain steel grades with good comprehensive properties, generally medium carbon steel, too low a carbon content can not guarantee sufficient hardness, and too high a carbon content will easily cause insufficient toughness or cold and heat fatigue, so the mold steel of the present invention For medium carbon steel.

(2) The Cr element can increase the hardenability of the steel. It can be dissolved in both austenite and martensite. The solid solution of Cr helps to improve the stability and martensite stability of supercooled austenite. Tensile temper resistance. However, if the Cr content is too high (such as 5% Cr in H13 steel), when tempering after quenching, chromium and carbon can form high-chromium carbides, hindering the formation of vanadium carbides with high resistance to temper softening , thereby reducing the high-temperature heat strength of H13 steel, so the present invention slightly reduces the Cr content.

(3) W and Mo are high thermal strength forming elements, which can improve the high temperature strength and thermal stability of steel. Mo forms Mo ₂ C-type stable carbides after heat treatment, which can improve the temper softening resistance of steel. However, when the W content is too high, the cold and heat fatigue resistance of the steel will be significantly reduced. Generally, the W content should not exceed 3%.

(4) V is also a carbide-forming element with excellent stability, which can reduce the process sensitivity of steel. The carbides of V are dispersed and precipitated, which hinders the growth of grains and achieves the effect of refining grains; in the process of high temperature tempering, V is prone to obvious secondary hardening effect.

(5) Si can improve the hardenability of steel and also help to increase the secondary hardening peak of steel, so Si is beneficial to improve the strength and tempering resistance of the matrix.

The step of electroslag remelting is adopted in the present invention, which can improve the metallurgical quality of steel ingots, reduce impurity elements such as P and S, and reduce component segregation. The high-temperature homogenization of electroslag ingots can improve the primary carbides, followed by forging to improve the structure and composition of the steel ingots, so as to ensure the good comprehensive properties of the steel.

The hot work die steel material prepared by the method of the invention has higher Rockwell hardness, better thermal fatigue performance and better impact toughness at room temperature.

Description of drawings

Fig. 1 is a comparison diagram of the hardness-time change curves of the hot work die steel of the present invention and H13 steel.

Quenching at 1060°C + tempering twice at 600°C and then holding at 600°C, the graphs of the HRC hardness values of the two steel materials, the die steel of the present invention and the H13 steel, as a function of the holding time.

Detailed ways

Embodiments of the present invention will now be described in detail below.

Example 1

In the present embodiment, the composition and weight percentage of the die steel that adopts are as follows:

Cr 3.64%

Mo 2.32%

V 1.29%

W 1.29%

Mn 0.36%

Ni 0.15%

C 0.32%

Si 0.27%

S 0.002%

P 0.01%

Fe balance

Process and steps in the present embodiment are as follows:

(1) Melting: smelting according to the traditional conventional method, placing the batch material according to the above formula in an intermediate frequency induction furnace, and smelting at a temperature above 1500°C; then casting the ingot, and entering the next step for use;

(2) Electroslag remelting: use electric current to generate resistance heat through the electroslag layer to melt the alloy base material of the consumable electrode. The liquid metal falls in the form of molten droplets through the slag layer into the metal molten pool in the water-cooled crystallizer. Gradually crystallize from bottom to top. 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. The alloy is further refined during remelting, and inclusions are removed by slag washing and floating in the molten pool. The durability and plasticity of the alloy are improved, and various macroscopic and microscopic defects are eliminated or alleviated;

(3) High-temperature homogenization: Then heat up to a temperature of 1200-1240°C and keep it warm for 9 hours to homogenize the steel composition, and then bury it in sand to cool;

(4) Forging: Then heat the above ingot to 1200-1230°C for rough forging, and the final forging temperature is 940°C to obtain forgings;

(5) Annealing of forgings: annealing at 830°C for 8 hours, then cooling with the furnace;

(6) Blank forging: reheat to 1100-1300°C, and perform forging again in the temperature range of 930-1100°C;

(7) Annealing: at 810°C, anneal again for 7 hours, then cool with the furnace, and finally obtain the product hot work die steel.

Performance Testing

1. Hardness and impact toughness at room temperature under different conditions

The product hot working die steel that above-mentioned embodiment is obtained is done performance test, and the result is as follows:

(1) Quenching at 1020°C + twice tempering at 600°C

Its performance data are: hardness 49HRC, room temperature impact toughness value 275J.

(2) Quenching at 1060°C + twice tempering at 600°C

Its performance data is: hardness 50HRC, room temperature impact toughness value greater than 300J.

(3) Quenching at 1100°C + twice tempering at 600°C

Its performance data is: hardness 52HRC, room temperature impact toughness value greater than 300J.

2. The hardness-time change comparison between the mold steel of the present invention and the H13 steel

See Fig. 1 for the hardness-time variation curve comparison chart of the mold steel of the present invention and the H13 steel.

After quenching at 1060°C and tempering twice at 600°C, heat preservation at 600°C for two kinds of steel materials, that is, the change of the HRC hardness value of the die steel of the present invention and the H13 steel with the holding time, is clearly shown in the figure: ①The die steel of the present invention The hardness of the steel is significantly higher than that of the H13 steel under the same conditions, and it has better high temperature heat strength. ② The slope of the die steel of the present invention is obviously smaller than that of the H13 steel, which is relatively flat and stable, and has better resistance to tempering and softening than the H13 steel.

3. The thermal fatigue test comparison between the mold steel of the present invention and the H13 steel

After quenching at 1100°C + tempering twice at 600°C, the thermal fatigue test after 3000 cycles of the two steel types was observed by a stereoscopic electron microscope. It can be seen that the cracks on the surface of the mold steel of the present invention are significantly less than those of the H13 steel, and the crack group Small and uniform, distributed in a network without large cracks.

The composition and weight percentage of H13 steel as a comparison steel type are as follows:

Cr 5.06, Mo 1.55, V 1.04, W 0.029, Mn 0.443, C 0.395, Si 0.992, S 0.0062, P0.0165, Fe balance.

Claims (1)

1. A preparation method of high thermal strength hot work die steel, characterized in that the composition and weight percentage of the die steel are: Cr 3.5～4.0% Mo 2.0～2.5% V 1.0～1.5% W 1.0～1.5% Mn 0.1～0.5% Ni 0.1～0.25% C 0.3～0.35% Si 0.1～0.5% S 0.005～0.01% P 0.01～0.02% Fe balance; Concrete preparation process and steps are: (a) Melting: smelting according to the traditional conventional method, placing the batch material according to the above formula in an intermediate frequency induction furnace, and smelting at a temperature above 1500°C; then pouring steel ingots, and entering the next step for use; (b) Electroslag remelting: using electric current to generate resistance heat through the electroslag layer to melt the alloy base material of the consumable electrode, the liquid metal falls in the form of molten droplets through the slag layer into the metal molten pool in the water-cooled crystallizer, and the steel ingot is formed by Gradually crystallize from bottom to top; 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; the alloy is further refined during remelting, and inclusions are removed through slag washing and ingot. Floating in the molten pool; the durability and plasticity of the alloy are improved, and various macroscopic and microscopic defects are eliminated or alleviated; (c) Homogenization at high temperature: then heating to a temperature of 1200-1240°C, and keeping it warm for 8-10 hours to homogenize the composition of the steel ingot, and then bury it in sand to cool; (d) Forging: heating the above steel ingot to 1200-1230°C for rough forging, the final forging temperature is 940°C to obtain a forging; (e) Annealing of forgings: annealing at 830°C for 8 hours, then cooling in the furnace; (f) Blank forging: reheat to 1100-1300°C, and perform forging again in the temperature range of 930-1100°C: (g) Annealing: at 810°C, anneal again for 7 hours, then cool with the furnace, and finally obtain the product hot work die steel.

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