阅读说明：本技术 一种提高热模钢热硬性和高温耐磨性的热处理工艺 (Heat treatment process for improving hot hardness and high-temperature wear resistance of hot die steel ) 是由 苗昕旺 谷志刚 臧玉郡 王丹丹 刘希德 宋佳健 孙明 马宇 李金红 于 2019-10-12 设计创作，主要内容包括：一种提高热模钢热硬性和高温耐磨性的热处理工艺,将木炭、尿素颗粒、碳酸钠粉末和铬酐混合得到碳氮强渗合剂；将热模钢制工件和碳氮强渗合剂同时装入渗箱中,密封渗箱的箱盖；将渗箱放入坩埚式电炉中850℃～950℃恒温进行强渗碳氮,然后淬火处理后,将热模钢制工件直接浸入淬火油中冷却,空冷后,放入箱式中温回火炉中进行两次回火,得到高热硬性、高温高耐磨性热模钢工件。优点是：操作简便、成本低廉且效果明显,获得的热模钢表面硬度可达62HRC以上,在600℃温度下的高温耐磨性超过同种热模钢常规热处理件的2倍以上,可有效提高热作模具的使用寿命。(A heat treatment process for improving hot hardness and high-temperature wear resistance of hot die steel comprises mixing charcoal, urea particles, sodium carbonate powder and chromic anhydride to obtain strong carbon-nitrogen cementing agent; simultaneously loading a hot die steel workpiece and a strong carbonitriding agent into a infiltration box, and sealing a box cover of the infiltration box; and (3) putting the infiltration box into a crucible type electric furnace for strong infiltration carbonitriding at a constant temperature of 850-950 ℃, then directly immersing the hot die steel workpiece into quenching oil for cooling after quenching treatment, and putting the hot die steel workpiece into a box type medium temperature tempering furnace for tempering twice after air cooling to obtain the hot die steel workpiece with high hot hardness and high temperature and high wear resistance. The advantages are that: the method has the advantages of simple and convenient operation, low cost and obvious effect, the surface hardness of the obtained hot die steel can reach more than 62HRC, the high-temperature wear resistance at the temperature of 600 ℃ is more than 2 times of that of the conventional heat treatment piece of the same hot die steel, and the service life of the hot die can be effectively prolonged.)

1. A heat treatment process for improving hot hardness and high-temperature wear resistance of hot die steel is characterized by comprising the following steps of:

the method comprises the following specific steps:

(1) preparing strong carbonitriding agent

The strong carbon nitrogen cementing agent comprises the following components in percentage by weight: 43 to 48 percent of charcoal with the granularity less than or equal to 5 mm; 50 to 55 percent of urea particles with the granularity of 1 to 2 mm; 1.2 to 1.5 percent of sodium carbonate powder; 0.5 to 0.8 percent of chromic anhydride; mixing to obtain a strong carbonitriding agent;

(2) Strong cementation of carbon and nitrogen

welding a infiltration box by using a stainless steel plate, simultaneously filling a hot die steel workpiece and a strong carbonitriding agent into the stainless steel infiltration box, then uniformly sealing a box cover of the infiltration box after bentonite is formed into a mud shape by using water glass and water according to the mass ratio of 1: 2; then the infiltration box is put into a crucible type electric furnace which is heated to 800 ℃, the temperature is raised to 850-950 ℃, and the constant temperature is kept for 4-8 hours for strong infiltration carbonitriding;

(3) Quenching

After the constant-temperature strong-cementation carbonitriding is finished, heating the furnace temperature to the conventional quenching temperature of hot die steel for quenching treatment, discharging a stainless steel cementation box, opening the box, taking out a hot die steel workpiece in the box, directly immersing the hot die steel workpiece in quenching oil, cooling to 190-200 ℃, taking out the hot die steel workpiece, and air-cooling to room temperature;

(4) Tempering

And (3) putting the hot die steel workpiece subjected to strong carburization, carbonitriding and re-quenching into a box type medium-temperature tempering furnace, heating to 580 ℃, carrying out heat preservation and tempering for 2 hours, taking out of the furnace, carrying out oil cooling to room temperature, then putting into the tempering furnace for the second time, heating to 500 ℃, carrying out heat preservation and tempering for 1 hour, and carrying out oil cooling to room temperature to obtain the hot die steel workpiece with high hot hardness, high temperature and high wear resistance.

2. the heat treatment process for improving hot hardness and high temperature wear resistance of hot die steel as claimed in claim 1, wherein: the infiltration box is made of a 1Cr18Ni9Ti stainless steel plate with the thickness of 6mm by double-side welding.

3. The heat treatment process for improving hot hardness and high temperature wear resistance of hot die steel as claimed in claim 1, wherein: when the carbonitriding agent and the hot mould steel workpiece are boxed, the carbonitriding agent with the thickness of 20mm is uniformly paved at the bottom of the box, the hot mould steel workpiece is placed on the carbonitriding agent, the interval between the workpiece and the interval between the workpiece and the box wall are more than 10mm, the carbonitriding agent is filled in the workpiece and the box wall and tamped, and the vertical distance between the top of the hot mould steel workpiece and the inner surface of the box cover of the infiltration box is more than or equal to 40 mm.

4. the heat treatment process for improving hot hardness and high temperature wear resistance of hot die steel as claimed in claim 1, wherein: the quenching heating temperature is 1040 ℃, and the heat preservation is carried out for 0.5 to 1 hour for quenching treatment.

5. the heat treatment process for improving hot hardness and high temperature wear resistance of hot die steel as claimed in claim 1, wherein: the hot die steel is H11 steel, H13 steel or H21 steel.

6. The heat treatment process for improving hot hardness and high temperature wear resistance of hot die steel as claimed in claim 1, wherein: after the hot die steel is subjected to strong carbonitriding and composite heat treatment, the surface diffusion layer thickness is 1.8-2.0 mm.

7. The heat treatment process for improving hot hardness and high temperature wear resistance of hot die steel as claimed in claim 1, wherein: after the hot die steel is subjected to strong carburization, carbonitriding and composite heat treatment, the hardness of a surface carburized layer is 700HV_0.2～820HV_0.2To (c) to (d); the Rockwell hardness of the surface of the workpiece tempered at 580 ℃ can reach 64 HRC.

Technical Field

The invention relates to a heat treatment process for improving hot hardness and high-temperature wear resistance of hot die steel, in particular to a heat treatment process for improving hot hardness and high-temperature wear resistance of hot die steel by carrying out composite heat treatment of strengthening and carburizing carbonitriding elements on common hot die steel with high alloy content, such as 4Cr5MoSiV (H11), 4Cr5MoSiV1(H13) and 3Cr2W8V (H21) to increase the content of carbon and nitrogen in the surface layer of the hot die steel and then quenching.

Background

Hot work die steel is a steel grade used for manufacturing high temperature solid and liquid metal forming dies in the hot work forming production of metal products. The hot working die mainly comprises a hot forging die, a hot extrusion die, a die-casting die and the like, and in the hot forming production process, the die bears larger pressure and impact force, and simultaneously, after repeatedly contacting with high-temperature metal, the surface of the die also bears extremely high hot abrasion, cold and hot fatigue, hot corrosion and the like. Therefore, the hot working mold must have high temperature strength and hot hardness, high temperature softening resistance, thermal fatigue and thermal wear resistance, and high toughness, oxidation resistance and corrosion resistance. Research shows that the failure modes of the high-alloy hot-working die in the production process are mainly high-temperature thermal wear failure and cold-hot fatigue failure, so that the improvement of the high-temperature strength and the high-temperature hardness (hot hardness) of the surface of the high-alloy hot-working die is a main way for prolonging the service life of the high-alloy hot-working die.

At present, high alloy hot-work die steel commonly used at home and abroad, such as 4Cr5MoSiV (H11), 4Cr5MoSiV1(H13), 3Cr2W8V (H21) and other materials, contains more elements such as Cr, Mo, Si, W, V and the like which can improve tempering stability, hot hardness, hardenability and refined crystal grains, after the die is manufactured, the die is generally quenched at 1050-1150 ℃ and then tempered for a plurality of times at 500-650 ℃, so that the steel die can obtain fine needle tempering, retained austenite and a small amount of granular alloy carbide, has good strength and hardness and enough impact toughness, but for the high-temperature strength, the high-temperature hardness, the hot hardness and the high-temperature wear resistance of the steel, although the fixed hot processing and heat treatment specifications for the high alloy hot die steel for the common hot extrusion molding and die casting molding at home and abroad can ensure the normal hot extrusion and die casting molding production of metal materials, but because the final heat treated high-temperature hardness and high-temperature hardness are not high, generally, the wear resistance is between 45HRC and 50HRC, and the problems of easy softening at high temperature and easy wear at high temperature still exist, so that the service life of the die is not high generally. The hot working die material is expensive, the manufacturing cost of the die is high, and if the service life is too long, the production cost of the product is too high.

In order to prolong the service life of a high-alloy hot-working die, many researchers have done a lot of research work on how to improve the surface property of the die steel for many years, and the research work is already applied to production, and certain results are obtained. The method mainly comprises the following steps: carburizing the surface of the die by a high-temperature gas or solid method, low-temperature ion nitriding, nitrocarburizing by a low-temperature salt bath method, multi-element co-carburizing by a low-temperature salt bath method, modifying the surface of the die by a high-energy beam and the like. Although the surface strengthening method can improve the surface high-temperature performance of the hot die steel to different degrees, the method has the problems of unobvious effect, overhigh production cost, complex operation, unsuitability for application in medium and small enterprises and the like. Therefore, it is necessary to research an effective process which is simple and convenient to operate, low in cost, obvious in effect, strong in adaptability and suitable for surface chemical heat treatment strengthening of high-alloy-content hot die steel.

disclosure of Invention

the invention aims to solve the technical problem of providing a heat treatment process which is simple and convenient to operate, low in cost, obvious in effect and suitable for medium-sized and small enterprises and can improve the hot hardness and the high-temperature wear resistance of hot die steel, the surface hardness of the obtained hot die steel can reach over 62HRC, the surface hardness of the hot die steel can still be kept over 64HRC after the hot die steel is heated for a long time at 600 ℃, the high-temperature wear resistance of the hot die steel at the temperature of 600 ℃ is more than 2 times of that of a conventional heat treatment piece of the same hot die steel, and the service life of a hot die can be effectively prolonged.

The technical solution of the invention is as follows:

A heat treatment process for improving hot hardness and high-temperature wear resistance of hot die steel comprises the following specific steps:

(1) Preparing strong carbonitriding agent

the strong carbon nitrogen cementing agent comprises the following components in percentage by weight: 43 to 48 percent of charcoal with the granularity less than or equal to 5 mm; 50 to 55 percent of urea particles with the granularity of 1 to 2 mm; 1.2 to 1.5 percent of sodium carbonate powder; chromic anhydride (CrO)₃)0.5 to 0.8 percent; mixing to obtain a strong carbonitriding agent;

(2) Strong cementation of carbon and nitrogen

Welding a infiltration box by using a stainless steel plate, simultaneously filling a hot die steel workpiece and a strong carbonitriding agent into the stainless steel infiltration box, and uniformly sealing a box cover of the infiltration box after bentonite is formed into a mud shape by using water glass and water according to the mass ratio of 1: 2; then the infiltration box is put into a crucible type electric furnace which is heated to 800 ℃, the temperature is raised to 850-950 ℃, and the constant temperature is kept for 4-8 hours for strong infiltration carbonitriding;

(3) Quenching

After the constant-temperature strong-cementation carbonitriding is finished, heating the furnace temperature to the conventional quenching temperature of hot die steel for quenching treatment, discharging a stainless steel cementation box, opening the box, taking out a hot die steel workpiece in the box, directly immersing the hot die steel workpiece in quenching oil, cooling to 190-200 ℃, taking out the hot die steel workpiece, and air-cooling to room temperature;

(4) Tempering

and (3) putting the hot die steel workpiece subjected to strong carburization, carbonitriding and re-quenching into a box type medium-temperature tempering furnace, heating to 580 ℃, carrying out heat preservation and tempering for 2 hours, taking out of the furnace, carrying out oil cooling to room temperature, then putting into the tempering furnace for the second time, heating to 500 ℃, carrying out heat preservation and tempering for 1 hour, and carrying out oil cooling to room temperature to obtain the hot die steel workpiece with high hot hardness, high temperature and high wear resistance.

Furthermore, the infiltration box is formed by welding a 1Cr18Ni9Ti stainless steel plate with the thickness of 6mm on both sides.

Further, when the carbonitriding agent and the hot mould steel workpiece are boxed, firstly, the carbonitriding agent with the thickness of 20mm is uniformly paved at the bottom of the box, the hot mould steel workpiece is placed on the carbonitriding agent, the interval between the workpiece and the interval between the workpiece and the box wall are respectively more than 10mm, the carbonitriding agent is filled in the workpiece and the box wall and tamped, and the vertical distance between the top of the hot mould steel workpiece and the inner surface of the box cover of the infiltration box is more than or equal to;

Further, the quenching heating temperature is 1040 ℃, and the quenching treatment is carried out after the heat preservation for 0.5 to 1 hour.

Further, the hot die steel is H11 steel, H13 steel or H21 steel.

further, after the hot die steel is subjected to strong carburization, carbonitriding and composite heat treatment, the depth of the surface carburized layer reaches 1.8-2.0 mm; the microstructure of the surface layer is that granular and short rod-shaped alloy carbides are uniformly distributed on an acicular tempered martensite matrix; the metallographic structure of the H13 steel is shown in FIGS. 3 and 4.

Further, after the hot die steel is subjected to strong carburization, carbonitriding and composite heat treatment, the hardness of the surface carburized layer of the hot die steel is 700HV_0.2～820HV_0.2To (c) to (d); the Rockwell hardness of the surface of the test piece tempered at 580 ℃ can reach 64 HRC; wherein the abrasion resistance of the H13 steel at the high temperature of 600 ℃ is more than twice of that of a conventional quenched test piece.

Fundamental principles and performance of the invention

The hot-work die steel with high alloy content, such as 4Cr5MoSiV, 4Cr5MoSiV1, 3Cr2W8V, and the like, contains more alloy elements for improving the thermal stability and forming carbide, although the carbon content of the steel is only between 0.3 and 4.0 percent, the steel belongs to the range of hypereutectoid steel, is used as a hot-work die material at the temperature of below 600 ℃, has good high-temperature strength and hot hardness and certain toughness, and can meet the use requirements of most hot-work forming processing. However, the specified carbon content sometimes results in insufficient high temperature hardness of the mold surface in certain specific application environments, which results in early high temperature wear and softening and premature failure. If the carbon content of the whole mould is increased, the toughness of the mould matrix is reduced. The invention relates to a powder method hot die steel which is subjected to strong carburization carbonitriding and composite heat treatment (C-N + C method for short), and aims to improve the high-temperature hardness and the high-temperature wear resistance of the surface of a die by changing chemical components and metallographic structures in a certain depth of the surface layer of the die on the premise of not changing the core structure and the performance of the hot die steel die, so that the service life of the hot die is prolonged.

The surface layer structure of the test die can be completely different from that of the common quenching die by the means of high-temperature carbonitriding and then heating quenching composite heat treatment by using the charcoal, the urea, the sodium carbonate and the chromic anhydride carbonitriding agent. The surface structure of a common quenching die is lath-shaped tempered martensite (see figure 5), the surface of the die subjected to the (C-N + C) composite treatment is a fine acicular tempered martensite matrix on which dense granular and short rod-shaped alloy carbides and nitrides are uniformly distributed, and the existence of the carbides and the nitrides obviously plays roles in precipitation strengthening and dispersion strengthening on a steel matrix, so the hardness of the quenched die and the hardness of the quenched die after two times of tempering at different temperatures are obviously higher than those of the common quenching die. The carbon and nitrogen in these alloy carbides and nitrides originate from the strongly cementation process, while the alloying elements are inherent in the material. When the die after the strengthening and carburizing quenching is subjected to primary tempering at 580 ℃ and secondary tempering at 500 ℃, obvious secondary hardening is generated due to dispersion and precipitation of carbon and nitrogen compounds, and the hot hardness and the high-temperature wear resistance of the steel are improved. When the die is in service at the temperature of about 600 ℃, granular carbon and nitrogen compounds which are dispersed and distributed in the surface layer of the die play a pinning role in a martensite matrix, so that the movement and multiplication of dislocation in the die material are hindered under the action of high temperature and external force, and the internal slippage of metal is prevented, thereby improving the high-temperature strength and high-temperature wear resistance of the material and effectively prolonging the service life of the die.

The invention has the beneficial effects that:

H11, H13, H21 hot work die steel material for manufacturing hot extrusion die and die casting die is processed by charcoal, urea, sodium carbonate and chromic anhydride (C-N + C), the surface and the inside of the hot work die steel material can form a hardening area with the depth of more than 2mm, and the surface hardness can reach 820HV_0.2(ii) a After heating and heat preservation at 580 ℃, the high alloy content hot die steel workpiece treated by the (C-N + C method) can obtain a high carbon nitrogen hardened layer with the thickness of more than 2mm, the layer has good high-temperature mechanical property, and the Rockwell hardness of the surface of the workpiece at 600 ℃ can still reach 64 HRC; the result of the abrasion test piece shows that the abrasion resistance of the abrasion test piece at the high temperature of 600 ℃ is twice higher than that of the conventional quenching test pieceThe high-temperature wear-resistant composite material has high hot hardness and excellent high-temperature wear resistance, and simultaneously keeps good substrate toughness, so that the high-temperature service life of the type of die can be effectively prolonged, and the application field and the application range of the die material are enlarged. The composite heat treatment process (C-N + C) for carbonitriding quenching has the advantages of simple method, convenient operation, strong adaptability, no need of special equipment and low production cost, and is extremely suitable for metal hot extrusion and die-casting production of small and medium-sized enterprises.

drawings

FIG. 1 is a graph showing a carbonitriding quenching composite heat treatment (C-N + C) process according to the present invention (corresponding to example 1);

FIG. 2 is a schematic view of a carbonitrided workpiece loaded into a diffusion box and encapsulated as used in the present invention;

FIG. 3 is a metallographic structure diagram of a surface layer of a H13 steel test piece obtained by the present invention (corresponding to example 1) at 50 Xmagnification;

FIG. 4 is a metallographic structure diagram of a surface layer of a H13 steel test piece obtained by the present invention (corresponding to example 1) at 500 Xmagnification;

FIG. 5 is a metallographic structure diagram of a structure of a conventional quenched surface layer of H13 steel obtained by the present invention (corresponding to comparative example 1) at 500 Xmagnification;

FIG. 6 is a comparison graph of the change in Rockwell hardness after carbonitriding quenching of H11, H13, and H21 steels according to the present invention (corresponding to example 1) and after tempering at different temperatures in a conventional quenching of H13 steels (corresponding to comparative example 1);

FIG. 7 is a graph showing the hardness of the surface layer after carbonitriding hardening (C-N + C) of H13 steel according to the present invention (corresponding to example 1) and conventional hardening (corresponding to comparative example 1);

FIG. 8 is a comparison of the results of the pin-on-disc type frictional wear test of the H13 steel carbonitriding quenched (C-N + C) according to the present invention (corresponding to example 1) and conventional quenched (corresponding to comparative example 1) at a high temperature of 600 ℃.

Detailed Description