CN114427091A

CN114427091A - High-wear-resistance die steel product for hot stamping and additive manufacturing process thereof

Info

Publication number: CN114427091A
Application number: CN202011093740.6A
Authority: CN
Inventors: 孙正启; 陈扬; 刘明旺; 范成景; 孙乾钊
Original assignee: Wuxi Langxian Lightweight Technology Co ltd
Current assignee: Wuxi Langxian Lightweight Technology Co ltd
Priority date: 2020-10-14
Filing date: 2020-10-14
Publication date: 2022-05-03
Anticipated expiration: 2040-10-14
Also published as: CN114427091B

Abstract

The invention provides a high-wear-resistance die steel product for hot stamping and an additive manufacturing process thereof, wherein the die steel product comprises a cladding layer and a substrate which are arranged up and down, the cladding layer is made of high-speed steel, and the substrate is made of high-strength steel; the thickness of the cladding layer is 1-10mm, and the hardness is 52-62 HRC; the cladding layer comprises 0.6-0.9% of C and 5.0-11.0% of Cr + Mo + V; the thickness of the base body is 40-400mm, the hardness is 30-45HRC, a water channel is arranged in the base body, the diameter of the water channel is 5-15mm, and the distance from the water channel to the molded surface of the product is 5-20 m. The invention utilizes the characteristics of high energy density and rapid cooling of laser cladding and is matched with the design of wear-resistant powder components to realize high alloying and segregation-free of a cladding layer so as to improve the wear resistance and the cracking resistance of the die steel and reduce the manufacturing cost of die steel products.

Description

High-wear-resistance die steel product for hot stamping and additive manufacturing process thereof

Technical Field

The invention mainly relates to the technical field of die steel manufacturing, in particular to a high-wear-resistance die steel product for hot stamping and a material increase manufacturing process thereof, which are suitable for manufacturing die steel products such as hot stamping die inserts, hot cutter blocks, hot stamping punches and the like.

Background

With the development of weight reduction of automobiles, material processing techniques typified by hot stamping have been developed vigorously. It uses the principle of metal high-temperature plastic forming to complete the plastic forming of hot-press hardening steel such as 22MnB5 at 650-850 ℃, and carries out cold die quenching treatment on the plate under the pressure of 5-15 MPa. Compared with a high-strength steel cold stamping process, the process has the advantages that parts are almost free of springback, complex molded surface forming can be achieved, and the like, and the process quickly becomes a mainstream technology for achieving light weight of automobiles, and the market of related die steel reaches 100-200 million yuan/year. Generally, a hot stamping die is required to have a service life as long as 20-40 ten thousand times, and due to the fact that the hot stamping die bears cold and hot cyclic stress, friction and local stress concentration (waterway processing) generated by plate material flowing and domestic hot stamping equipment is unstable, service working conditions are complex and severe, and requirements on alloy design, purity and structure regulation and control of die steel are severe.

At present, hot stamping die steel is generally processed by adopting modes of component design, vacuum refining, electroslag remelting, isotropic forging and the like, so that the service life of the die steel is ensured. Patent No. CN101302599A, patent name: niobium microalloyed high-strength hot work die steel and a preparation method thereof, and provides a preparation process of the hot work die steel, which prepares the die steel by refining, electroslag remelting, homogenizing annealing and multidirectional forging. The equipment investment is high, the production process is complex, the manufacturing cost is extremely high, the industrial production almost comes from import, and related products account for more than 30% of the cost of the die.

In addition, the non-plating plate is adopted for hot stamping in China, a large amount of oxide skin is generated in the austenitizing process, so that the abrasion of the die insert and the punch abrasive grains and the adhesive abrasion are serious, the existing die is maintained very frequently, and the profile is subjected to profile reduction or die remaking every 10 ten thousand punching times due to the out-of-tolerance of the profile caused by the abrasion of the R angle of the die. Meanwhile, due to the instability of the production line, the frequency of mould cracking and scrapping is extremely high due to abnormal stamping such as material stacking of the plates and retention of impurities in the mould. Therefore, the existing die steel product, whether in component design or preparation process, cannot meet the requirements of hot stamping working condition and service life.

In summary, the existing hot stamping die steel utilizes electroslag remelting and other processes, and has the problems of macrosegregation, high manufacturing cost and low utilization rate of alloy elements, and the wear resistance can not meet the requirements of hot stamping complex working conditions.

In recent years, laser cladding is an advanced local material modification technology, and a powder and a substrate surface are fused together by a high-density laser beam through a coaxial powder feeding method and the like, so that a metallurgically bonded alloy layer is formed on the surface of a substrate. Patent application No. CN101392382B, patent name: a method and a device for strengthening surface modification by combining laser cladding with laser shot peening are provided, which combine laser cladding with shot peening to improve alloy performance. Patent application No. CN107164756B, patent name: a metal powder for repairing H13 die steel by laser cladding, provides C-Cr-Mo series iron-based powder, and performs surface repair on H13 steel by laser cladding. However, related research focuses on the fields of laser repair and local reinforcement, and no one is applied to the integrated manufacturing of the die steel product. More importantly, the method is limited by component design and cladding processes, the existing powder is generally low-carbon alloy steel and maraging steel, the content of carbide is low, the strength of a matrix is low, early wear failure of the die steel is caused, or micron-sized particles such as WC and SiC are added, and the die steel generates thermal stress fatigue within 5 ten thousand punching times. Therefore, the related products cannot meet the working condition requirement of hot stamping.

In conclusion, the high-wear-resistance die steel powder suitable for laser cladding is designed, the laser cladding process is improved, the structure and the performance of the die steel are superior to those of the existing hot stamping die steel, and the die steel powder also becomes a big problem in the field of additive manufacturing of the hot stamping die steel.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a high-wear-resistance die steel product for hot stamping, which comprises a cladding layer and a substrate, wherein the cladding layer and the substrate are arranged up and down;

the thickness of the cladding layer is 1-10mm, and the hardness is 52-62 HRC; the cladding layer comprises 0.6-0.9% of C and 3.0-6.0% of Cr + Mo + V; the cladding layer has higher wear resistance and tempering resistance;

the thickness of the base body is 40-400mm, the hardness is 30-45HRC, a water channel is arranged in the base body, the diameter of the water channel is 5-15mm, and the distance from the water channel to the molded surface of the product is 5-20 m.

Preferably, the high speed steel further comprises one or more of Si, Mn, Nb, Ti and Co.

Preferably, the cladding layer is provided with an intermediate layer, the intermediate layer is positioned in the transition between the cladding layer and the substrate, and the intermediate layer serves as a transition layer between the cladding surface layer and the substrate according to process requirements, so that the cladding formability of the surface alloy is improved, and thermal stress and phase change stress cracking are avoided.

Preferably, the matrix comprises the following components: 0.3 to 0.5 percent of C, 0.2 to 1.0 percent of Si, 0.4 to 1.5 percent of Mn, 0.2 to 2.0 percent of Cr and Mo, and the balance of Fe and impurities;

the cladding layer comprises the following components: 0.6 to 0.9 percent of C, 0.4 to 1.0 percent of Si, 0.5 to 1.0 percent of Mn + Ni, 4.0 to 8.0 percent of Cr + Mo + V, 0 to 0.5 percent of Nb + Ti and 0 to 3.0 percent of Co.

The alloy powder for the manufacture of the cladding layer has the following composition-limiting reasons:

1) 0.6 to 0.9 percent of carbon C. The most basic strengthening element in steel is also a key element for improving the hardness and wear resistance of materials. In the form of solid solution and carbide, and form carbide with Cr, Mo and V to raise the strength of the alloy. The research shows that the instantaneous highest temperature of the mold surface is 200-350 ℃ in the process of hot stamping and pressure maintaining of the plate. Therefore, tempering softening is not the main failure mode of the hot stamping die, and the existing die forged steel generally adopts hot-work die steel and does not meet the requirements of actual working conditions. However, the ductility and toughness of the alloy are reduced due to the excessively high content of C, the cladding cracking sensitivity is increased, and the corner collapse and stress fatigue are easy to occur in the hot stamping process. Therefore, the content of C is controlled to be 0.6-0.9 percent.

2) 0.4 to 1.0 percent of silicon Si. Exists in a solid solution form, and is beneficial to improving the room temperature strength, the hot strength and the cutting processing performance of the steel. In addition, certain Si is added into the die steel and is matched with Mo and Cr for use, so that the corrosion resistance and the oxidation resistance of the die steel can be improved, the oxidation behavior of a die steel product in the using process and the corrosion of cooling water to the inner wall of a die steel water channel are effectively inhibited, and the stress corrosion cracking of the die steel is avoided. The invention controls the Si content at 0.2-1.0%.

3) 0.2 to 1.0 percent of manganese plus nickel Mn plus Ni. Existing in a solid solution form, austenite stabilizing elements expand an austenite phase region and mainly play a role in solid solution strengthening. Meanwhile, Mn is a good deoxidizer and desulfurizer, the brittle transition temperature can be effectively reduced, and a certain amount of Mn can eliminate or reduce the thermal brittleness caused by P, S. And a certain amount of Mn and Ni is added, so that the cladding cracking sensitivity of the material can be reduced.

4) 5.0-11.0% of Cr + Mo + V. The carbide forming element can obviously improve the hardenability and the thermal stability of the die steel. In die steels, mainly in the form of carbide second phases, are important elements in determining die steel hardness and wear resistance. However, when the content is high or the compounding ratio is not proper, the toughness of the material is rapidly deteriorated. Researches show that the existing hot stamping die steel generally adopts higher Mo and V, can improve the yield point, the room temperature strength and the high temperature strength of the material, and a certain amount of Cr and Mo can also improve the corrosion resistance of the material, thereby avoiding the early cracking of a die steel runner. Wherein V can form more dispersed carbide and play a role in refining grains. However, when the content is too large, the cladding layer has more residual austenite, and needs to be tempered for removing, otherwise the service performance is unstable, and adhesive wear occurs.

5) 0 to 0.5 percent of niobium, titanium Nb and Ti. The strong carbide-forming elements, non-essential elements, in steel exist mainly in the form of dispersed carbides, which are used to strengthen the matrix grains. As the laser cladding solidification speed is higher, researches show that the addition of a certain amount of Nb and Ti can effectively refine the structure of the cladding layer, and improve the toughness, thermal stability and fatigue life of the hot stamping die. In addition, Ti has strong affinity with N, O, and can perform deoxidation effect to reduce coarse oxide inclusion in the cladding layer. Therefore, the Nb + Ti content is controlled to 0-0.5%.

6) 0 to 3.0 percent of cobalt Co. The compressive strength of the cladding layer on the surface of the die steel product can be improved in a solid solution strengthening mode. The die is used for die products such as hot cutter blocks, hot stamping punches and the like which bear large extrusion force, effectively inhibits the fatigue of early strain of the products caused by unstable service, and prolongs the service life of die steel products manufactured by laser cladding.

The preferred substrate composition for the die steel article is limited for the following reasons:

as the hot stamping holding pressure is usually controlled to be 5-25MPa, the high-strength die steel is not needed for the die steel product substrate. On the basis of the existing die steel, the invention properly reduces the contents of C, Cr, Mo and V, and improves the ductility and toughness by 2-3 times; compared with similar forged steel and additive manufacturing products, the method effectively inhibits the cracking risk of the die steel product caused by unstable machine tool or local stress concentration. In the invention, a certain amount of Ti, Nb and V are added, so that the grain refinement of the base material can be effectively improved, the thermal stability of the die steel product is also improved to a certain extent, and the tempering and softening of the base material caused by overhigh temperature due to the fact that a water path cannot be designed in products such as a hot cutter block and the like are prevented.

An additive manufacturing process for a high wear resistance die steel article for hot stamping, comprising the steps of:

s1: and (3) reducing the material of the base material: reducing the profile of the base material by taking the profile of the die steel product as a reference, wherein the over-cut amount of the profile of the base material is 0.1-5 mm;

s2: laser additive cladding: cleaning the surface of a base material, setting a feeding path of laser cladding according to the molded surface of a product, setting technological parameters of laser cladding according to the characteristics of cladding powder, controlling the pass overlapping rate to be 25-50%, the laser power to be 1-6kw, and the diameter of a light spot to be 0.2-3mm, cladding 1-4 layers of alloy layers on the surface of the base material, controlling the thickness of a single-layer alloy layer to be 0.1-3mm, and controlling the total thickness of cladding layers formed by the multiple alloy layers to be 0.2-2mm higher than the overcut amount of the base material;

s3: tempering the product: tempering the die steel product, wherein the tempering temperature is 450-600 ℃, and the tempering frequency is 1-3, because the cooling rate is as high as 100-1000 ℃/s in the laser cladding process, and the cladding layer structure is mainly martensite and retained austenite. Residual austenite and martensite in the cladding layer are eliminated through tempering, and the thermal stability and the anti-adhesion wear characteristic of the die steel cladding alloy layer are improved;

s4: and (3) finish machining of the product: and (4) performing material reduction processing on the area of the product cladding layer higher than the molded surface by taking the molded surface of the product as a reference to obtain a finished product.

Preferably, in step S2, the product substrate is preheated or heated on line according to the composition system characteristics of the powder and the substrate and the cladding process requirements, so that the temperature of the product substrate reaches 250-400 ℃;

when the product substrate is preheated, the heating temperature is 300-450 ℃;

when the product substrate is heated in-line, the heating temperature is 250-400 ℃.

The invention has the beneficial effects that: utilize laser cladding's high energy density and quick cooling characteristic, the cooperation is with the design of wearability powder composition, realizes that the high alloying of cladding layer, segregation-free improve the wearability and the anti fracture performance of mould steel, reduces the manufacturing cost of mould steel product, and is specific:

1. higher wear resistance: the content of C is 0.6-0.9%, the content of carbide is improved, fine matrix grains are obtained through the rapid cooling characteristic of laser cladding, and the compressive strength of the material is improved and the adhesive wear and extrusion deformation are reduced due to the addition of Co;

2. the hot cracking resistance is good: the surface stress in the processing process of the die steel product is reduced by preheating or online heating, and the cladding requirement of high-carbon equivalent powder can be met;

3. the die steel product has low cost: the product base material is selected from conventional alloy steel or carbon steel, only a high-performance alloy layer needs to be cladded on the surface layer, the consumption of expensive elements is low, the requirement of a simpler manufacturing process is met, and the manufacturing cost of the die steel is reduced by more than 50%;

4. the alloy utilization rate is high: the incoming material state of the traditional die steel product is square or round, the machining of the molding surface is completed by a material reducing machine cutter, the material utilization rate can only reach 50-75%, the die steel product is prepared by adopting laser cladding, the material utilization rate is up to more than 90%, and the cost of the die steel surface layer only needs to be controlled;

5. the product segregation is small: the laser has high energy density, can melt the material with high alloy content and realize the extremely rapid cooling of the material, so the crystal grain is finer and the alloy layer has almost no macrosegregation.

Drawings

FIG. 1 is a perspective view of a die steel article according to the present invention;

FIG. 2 is a front view of the present invention in relation to a die steel article;

FIG. 3 is a schematic plan view of the material increasing and decreasing process of the present invention, wherein a is a substrate, b is a material decreasing process of the substrate, c is laser material increasing and cladding, and d is a finish process of the product;

FIG. 4 is a perspective view of the present invention relating to material increase and decrease processing;

FIG. 5 is a schematic representation of the alloy layer structure of an article of the present invention;

FIG. 6 is a schematic view of the product of the present invention applied to a hot stamping die;

FIG. 7 is a schematic view of the product of the present invention applied to the lower die of a hot stamping die;

wherein:

1. an insert profile; 2. a waterway system; 3. the distance of the waterway from the molded surface; 4. the distance between the water paths; 5. an upper die holder; 6. an upper die insert (laser additive manufacturing); 7. a lower die insert (laser additive manufacturing); 8. a lower die holder; 9. a guide mechanism.

Detailed Description

In order to make the technical solutions of the present invention better understood and make the above features, objects, and advantages of the present invention more comprehensible, the present invention is further described with reference to the following examples. The examples are intended to illustrate the invention only and are not intended to limit the scope of the invention.

As shown in fig. 3 to 4, a high wear resistance die steel product for hot stamping according to the present invention includes: the steel plate comprises a cladding layer and a substrate which are arranged up and down, wherein the cladding layer is made of high-speed steel, and the substrate is made of high-strength steel;

the thickness of the cladding layer is 1-10mm, and the hardness is 52-62 HRC; the cladding layer comprises 0.6-0.9% of C and 3.0-6.0% of Cr + Mo + V;

In addition, according to the process requirement, an intermediate layer is arranged between the cladding layer and the matrix and serves as a transition layer between the cladding surface layer and the matrix, so that the cladding formability of the surface alloy is improved, and thermal stress and phase change stress cracking are avoided.

In this embodiment, the matrix preferably comprises the following components: 0.3 to 0.5 percent of C, 0.2 to 1.0 percent of Si, 0.4 to 1.5 percent of Mn, 0.2 to 2.0 percent of Cr and Mo, and the balance of Fe and impurities;

s3: tempering the product: tempering the die steel product at 450-600 ℃ for 1-3 times; the reason is that in the laser cladding process, the cooling rate is as high as 100-1000 ℃/s, and the cladding layer structure mainly comprises martensite and retained austenite. Through tempering, residual austenite and martensite in the cladding layer are eliminated, and the thermal stability and the anti-adhesion wear property of the die steel cladding alloy layer are improved.

Preferably, in the present embodiment, in step S2, the substrate of the product is preheated or heated on-line according to the composition system characteristics of the powder and the substrate and the cladding process requirements, so that the temperature of the substrate of the product reaches 250-400 ℃;

Specifically, the following examples are set forth to illustrate:

for an insert used for a hot stamping die, die forged steel such as Dievar, W360 and Q-grade H13 is mostly adopted in the prior industry, and the problem of high abrasion speed exists in a non-plating plate hot stamping environment. According to the table 1, on the basis of H13 die steel, the powder system HS-P improves the content of C to 0.70-0.80% and the content of Cr to 7.00-8.00% to improve the wear resistance of the material, and solves the problem that the R angle of an insert of a hot stamping die is easy to wear. Meanwhile, a layer of high-performance powder HS-P is cladded on the cheap base material HS-S through laser cladding, and the structure segregation-free and high fatigue performance of the cladded alloy layer HS-P is obtained. In addition, compared with the imported die steel on the market, the preparation cost is reduced by 50-75%.

Table 1: the die steel composition table of the invention

The preparation process comprises the following steps:

1) preparation of powder: HS-P powder was prepared by gas atomization and the powder was sieved to obtain a powder with a particle size of 10-150 microns.

2) Preparing a base material: the HS-S base material is prepared by a casting-forging method, and the heat treatment hardness is controlled to be 38-40 HRC. See fig. 3-4 (a).

3) And (3) reducing the material of the base material: the base material was cut into pieces and over-cut by 2.5mm depending on the molded surface of the product. See FIGS. 3-4 (b).

4) Stress relief annealing: the substrate is stress-relieved annealed at 300-400 c, and subsequently, the substrate surface is cleaned with an acetone solvent.

5) Laser additive cladding: cladding 2 layers on the surface of the substrate, controlling the thickness of a single layer to be 1.6mm, controlling the pass overlapping rate to be 30-40%, and selecting 2KW as laser power. See FIGS. 3-4 (c).

6) Tempering treatment: and tempering the product at 500-550 deg.c for 3 times, with the hardness of the cladding layer controlled at 56-60 HRC.

7) And (3) finish machining of the product: and (3) performing cutting and material reducing processing on the area (1.6 x 2-2.5 mm is 0.7mm) of the higher profile of the cladding layer by taking the profile of the product as a reference, and finishing the preparation of the die insert. See FIGS. 3-4 (d).

Second, organization and Performance comparison

The following is a comparison with a Q-grade H13 material commonly used in hot stamping. The H13 die steel comprises 0.35-0.42% of C, 0.20-0.50% of Mn, 0.80-1.20% of Si, 4.75-5.50% of Cr, 0.80-1.20% of V and 1.20-1.50% of Mo, and is processed by vacuum melting, electroslag remelting, multidirectional forging and other processes. Generally, the structure characteristics of H13 die steel have macrosegregation bands which are not eliminated during tempering, and the matrix has uneven grain size distribution and coarse grains. FIG. 5 shows the structure of the cladding layer of the HS die steel product of the invention, and although a small amount of pore defects exist, the structure is finer and no macrosegregation band exists in the structure.

Through comparison of actual service of hot stamping, the HS die steel has the failure mode of mainly abrasion without integral cracking. The matrix material HS-S of the die steel product has the plasticity and toughness far higher than that of H13 die steel, and can effectively prevent the crack of the cladding layer from expanding to the matrix when receiving unstable loading force; cracks generated in the H13 die steel can extend to the water channel, and the die insert leaks water and is early scrapped. In addition, the profile temperature of the HS die steel product is maintained between 100 and 120 ℃ while the profile temperature of the H13 die steel is maintained between 110 and 135 ℃ during continuous production, which also indicates that the HS die steel product has better heat conduction performance. Specific results are shown in the following table:

table: the invention is compared with the performance of the same type die steel product

The above-described embodiments are merely illustrative of the principles and utilities of the present patent application and are not intended to limit the present patent application. Modifications and variations can be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of this patent application. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical concepts disclosed in the present application shall be covered by the claims of this patent application.

Claims

1. A high-wear-resistance die steel product for hot stamping is characterized by comprising a cladding layer and a substrate which are arranged up and down, wherein the cladding layer is made of high-speed steel, and the substrate is made of high-strength steel;

the thickness of the cladding layer is 1-10mm, and the hardness is 52-62 HRC; the cladding layer comprises 0.6-0.9% of C and 5.0-11.0% of Cr + Mo + V;

2. A high wear resistance die steel article for hot stamping according to claim 1, wherein: the high speed steel further comprises one or more of Si, Mn, Nb, Ti and Co.

3. A high wear resistance die steel article for hot stamping according to claim 2, wherein: the cladding layer is provided with an intermediate layer, and the intermediate layer is located at the transition between the cladding layer and the substrate.

4. A high wear resistance die steel article for hot stamping according to claim 3, wherein: the matrix comprises the following components: 0.3 to 0.5 percent of C, 0.2 to 1.0 percent of Si, 0.4 to 1.5 percent of Mn, 0.2 to 2.0 percent of Cr and Mo, and the balance of Fe and impurities;

5. An additive manufacturing process for a high wear resistance die steel article for hot stamping, comprising the steps of:

s3: tempering the product: tempering the die steel product at 450-600 ℃ for 1-3 times;

6. The additive manufacturing process for a high wear resistant die steel article for hot stamping according to claim 5, wherein: in the step S2, the product substrate is preheated or heated on line according to the component system characteristics of the powder and the substrate and the cladding process requirements, so that the temperature of the product substrate reaches 250-400 ℃;