CN114427091B

CN114427091B - High-wear-resistance die steel product for hot stamping and additive manufacturing process thereof

Info

Publication number: CN114427091B
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: 2024-03-26
Anticipated expiration: 2040-10-14
Also published as: CN114427091A

Abstract

The invention provides a high-wear-resistance die steel product for hot stamping and an additive manufacturing process thereof, comprising a cladding layer and a matrix, wherein the cladding layer is made of high-speed steel, and the matrix is made of high-strength steel; the thickness of the cladding layer is 1-10mm, and the hardness is 52-62HRC; the cladding layer comprises 0.6-0.9% of C and 5.0-11.0% of Cr+Mo+V; the thickness of the matrix is 40-400mm, the hardness is 30-45HRC, a waterway is arranged in the matrix, the diameter of the waterway is 5-15mm, and the distance between the waterway and the molded surface of the product is 5-20m. The invention utilizes the high energy density and rapid cooling characteristic of laser cladding, and is matched with the design of wear-resistant powder components, thereby realizing high alloying of the cladding layer, improving the wear resistance and cracking resistance of the die steel without segregation and reducing the manufacturing cost of the die steel product.

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 an additive manufacturing process thereof, which are suitable for manufacturing die steel products such as hot stamping die inserts, hot cutting 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 vigorously developed. The method utilizes the principle of metal high-temperature plastic forming, finishes plastic forming of the 22MnB5 hot-press hardened steel at 650-850 ℃ and carries out cold die quenching treatment on the plate under the pressure of 5-15 MPa. Compared with the high-strength steel cold stamping process, the cold stamping process has the advantages of almost no rebound of parts, capability of realizing complex profile forming and the like, and rapidly becomes a mainstream technology for realizing the weight reduction of automobiles, and the market of relevant die steel is as high as 100-200 hundred million yuan/year. In general, a hot stamping die is required to have service life as long as 20-40 ten thousand times, and is complicated and severe in service working condition due to bearing cold and hot circulating stress, friction generated by plate flowing and local stress concentration (waterway processing) and unstable domestic hot stamping equipment, and extremely severe in alloy design, purity and structure regulation and control requirements of die steel.

At present, hot stamping die steel is usually processed by adopting modes such as component design, vacuum refining, electroslag remelting, isotropic forging and the like, so that the service life of the die steel is ensured. Published invention patent, patent number CN101302599a, patent name: a niobium microalloying high strength hot work die steel and a preparation method thereof, which provides a preparation process of the hot work die steel, wherein the die steel is prepared through 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 industry almost comes from import, and related products occupy more than 30% of the die cost.

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 abrasive particles of the die insert and the punch are worn seriously, the existing die is maintained very frequently, the molded surface is out of tolerance due to the abrasion of the R angle of the die, and the molded surface is reduced or the die is remade every 10 ten thousand times of punching. Meanwhile, due to instability of a production line, the frequency of die cracking and scrapping caused by abnormal stamping of plate material stacking, sundry retention dies and the like is extremely high. Therefore, the existing die steel products cannot meet the requirements of hot stamping working conditions and service life no matter the existing die steel products are designed by components or prepared by a process.

In summary, the existing hot stamping die steel has the problems of macrosegregation, high manufacturing cost and low utilization rate of alloy elements by utilizing processes such as electroslag remelting and the like, and the wear resistance cannot meet the requirements of hot stamping complex working conditions.

In recent years, laser cladding has been used as an advanced material local modification technique, which fuses powder and a substrate surface together by a laser beam of high bulk density by a method such as coaxial powder feeding, thereby forming a metallurgically bonded alloy layer on the substrate surface. Published invention patent, application number CN101392382B, patent name: a method and a device for modifying the surface of laser cladding and laser shot peening are provided, which combine laser cladding and shot peening to improve the alloy performance. Published invention patent, application number CN107164756B, patent name: a metal powder for repairing H13 die steel for laser cladding is provided, which is C-Cr-Mo iron-based powder, and the surface of H13 steel is repaired by laser cladding. However, the related research is focused on the fields of laser repair and local reinforcement, and no one is applied to the integrated manufacturing of die steel products. More critical, the existing powder is usually low-carbon alloy steel and maraging steel, the carbide content is low, the matrix strength is low, early wear failure of the die steel is caused, or micron-sized particles such as WC and SiC are added, so that the die steel is subjected to thermal stress fatigue within 5 ten thousand times of impact. Therefore, the related products cannot meet the working condition requirements of hot stamping.

In summary, the design of the high-wear-resistance die steel powder suitable for laser cladding, and the improvement of the laser cladding process, the tissue and the performance superior to those of the existing hot stamping die steel are obtained, and the method also becomes a great difficulty in the field of hot stamping die steel additive manufacturing.

Disclosure of Invention

In order to overcome 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 matrix, wherein the cladding layer is made of high-speed steel, and the matrix is made of high-strength steel;

the thickness of the cladding layer is 1-10mm, and the hardness is 52-62HRC; 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 stability;

the thickness of the matrix is 40-400mm, the hardness is 30-45HRC, a waterway is arranged in the matrix, the diameter of the waterway is 5-15mm, and the distance between the waterway and the molded surface of the product is 5-20m.

Preferably, the high speed steel further comprises one or more of Si, mn, nb, ti and Co.

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

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

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

The reason why the composition of the alloy powder used for the production of the cladding layer is limited is as follows:

1) 0.6 to 0.9 percent of C. The most basic strengthening elements in steel are also key elements for improving the hardness and wear resistance of the material. In the form of solid solution and carbide, forms carbide with Cr, mo and V to improve alloy strength. It was found that the instantaneous maximum temperature of the die surface was 200-350 c during the hot stamping and pressure maintaining of the panel. Therefore, tempering softening is not a main failure mode of the hot stamping die, and the conventional die forging steel commonly adopts hot die steel and does not meet the requirements of actual working conditions. However, too high a C content reduces the toughness of the alloy, and the sensitivity to cladding cracking increases, and corner chipping and stress fatigue are liable to occur during hot stamping. Therefore, the invention controls the C content to be 0.6-0.9%.

2) 0.4 to 1.0 percent of Si. The solid solution form is favorable for improving the room temperature strength, the hot strength and the cutting processability 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 oxidation resistance of the die steel can be improved, the oxidation behavior of a die steel product in the use process and the corrosion of cooling water to the inner wall of a die steel water channel can be effectively inhibited, and the die steel stress corrosion cracking is avoided. The Si content is controlled to be 0.2-1.0%.

3) 0.2 to 1.0 percent of manganese, nickel Mn and Ni. The austenite stabilizing element exists in a solid solution form, enlarges the austenite phase region, and mainly plays a role in solid solution strengthening. Meanwhile, mn is a good deoxidizer and desulfurizing agent, can effectively reduce the brittle transition temperature, and a certain amount of Mn can eliminate or weaken the hot shortness caused by P, S. And a certain amount of Mn and Ni are added, so that the cladding cracking sensitivity of the material can be reduced.

4) 5.0 to 11.0 percent of chromium, molybdenum, vanadium, cr, mo and V. The carbide forming element can obviously improve the hardenability and the thermal stability of the die steel. In die steel, it exists mainly in the form of carbide second phase, which is an important element determining hardness and wear resistance of die steel. However, when the content is high or the ratio is improper, the toughness of the material is drastically deteriorated. The research shows that the existing hot stamping die steel generally adopts higher Mo and V, so that the yield point, the room temperature strength and the high temperature strength of the material can be improved, and a certain amount of Cr and Mo can also improve the corrosion resistance of the material, so that the early cracking of a die molten steel channel is avoided. Wherein, V can form more dispersed carbide to refine crystal grains. However, when the content is too high, the cladding layer is caused to have more retained austenite, and multiple tempering is required to eliminate the retained austenite, 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, and optional elements, in the steel are mainly in the form of dispersed carbides for strengthening the matrix grains. As the laser cladding solidification speed is higher, researches show that the structure of the cladding layer can be effectively refined by adding a certain amount of Nb and Ti, and the toughness, the thermal stability and the fatigue life of the hot stamping die are improved. In addition, ti has extremely strong affinity with N, O, can play a role in deoxidization, and reduces coarse oxide inclusions in the cladding layer. Thus, the Nb+Ti content is controlled to 0 to 0.5%.

6) Cobalt Co 0-3.0%. The compressive strength of the cladding layer on the surface of the die steel product can be improved by the solid solution strengthening mode. The method is used for die products with larger extrusion force, such as hot cutter blocks, hot punching heads and the like, so that fatigue of early strain of the products caused by unstable service is effectively inhibited, and the service life of the die steel products manufactured by laser cladding is prolonged.

The preferred substrate composition for die steel products is defined for the following reasons:

since the hot stamping dwell pressure is generally controlled to be 5-25MPa, high strength die steel is not required for die steel product substrates. The invention properly reduces the contents of C and Cr+Mo+V on the basis of the existing die steel, and improves the toughness by 2-3 times; compared with similar forged steel and additive manufactured products, the cracking risk of die steel products caused by unstable machine tools or local stress concentration is effectively restrained. In the invention, the grain refinement of the base material can be effectively improved by adding a certain amount of Ti, nb and V, the thermal stability of die steel products is also improved to a certain extent, and the tempering and softening of the base material caused by too high temperature generated by the fact that waterways cannot be designed in products such as hot cutting blocks and the like are prevented.

An additive manufacturing process for hot stamping high-wear-resistance die steel products, which is characterized by comprising the following steps of:

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

s2: laser additive cladding: cleaning the surface of a substrate, setting a feeding path of laser cladding according to the molded surface of the product, setting technological parameters of laser cladding according to the characteristic of cladding powder, controlling the pass lap ratio to be 25-50%, controlling the laser power to be 1-6kw, controlling the diameter of a light spot to be 0.2-3mm, cladding 1-4 alloy layers on the surface of the substrate, controlling the thickness of a single 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 over-cut of the substrate;

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

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

Preferably, in step S2, preheating or on-line heating is performed on the product substrate according to the component system characteristics of the powder and the substrate and the requirements of the cladding process, 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: by utilizing the high energy density and the rapid cooling characteristic of laser cladding and matching with the design of wear-resistant powder components, the high alloying and no segregation of the cladding layer are realized to improve the wear resistance and the cracking resistance of the die steel, and the manufacturing cost of the die steel product is reduced, specifically:

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

2. the heat crack resistance is good: the surface stress in the processing process of the die steel product is reduced by preheating or on-line heating, so that the cladding requirement of high-carbon equivalent powder can be met;

3. the die steel product has low cost: the substrate material of the product is conventional alloy steel or carbon steel, only a high-performance alloy layer is required to be clad on the surface layer, so that the consumption of expensive elements is low, the requirement of a simplified 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 traditional die steel product is square or round in feeding state, the profile processing is finished by a material reduction mechanical cutting tool, and the material utilization rate can only reach 50-75%, the die steel product is prepared by adopting laser cladding, the material utilization rate is as high as more than 90%, and only the cost of the die steel surface layer is required to be controlled;

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

Drawings

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

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

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

FIG. 4 is a schematic perspective view of the present invention for increasing or decreasing material processing;

FIG. 5 is a drawing of the structure of the alloy layer of the article of the present invention;

FIG. 6 is a schematic diagram 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 a lower die of a hot stamping die;

wherein:

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

Detailed Description

The present invention will be further described with reference to the following examples in order to better understand the technical solutions of the present invention and to make the above features, objects and advantages of the present invention more clearly understood. The examples are only for illustrating the present invention and are not intended to limit the scope of the present invention.

As can be seen from fig. 3 to 4, a high wear resistant die steel product for hot stamping according to the present invention comprises: the high-speed steel alloy comprises a cladding layer and a substrate, 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 52-62HRC; the cladding layer comprises 0.6-0.9% of C and 3.0-6.0% of Cr+Mo+V;

In addition, according to the technology needs, be provided with the intermediate level between cladding layer and the base member, the intermediate level acts as the transition layer between cladding top layer and the base member, and the purpose is to improve the cladding formability of top layer alloy, avoids taking place thermal stress and phase transition stress fracture.

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

s3: tempering the product: tempering the die steel product at 450-600 ℃ for 1-3 times; this is because the cooling rate is as high as 100-1000 deg.c/s during laser cladding, and the cladding layer structure is mainly composed of 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.

In the preferred embodiment, in step S2, the product substrate is preheated or heated online according to the component system characteristics of the powder and the substrate and the requirements of the cladding process, so that the temperature of the product substrate reaches 250-400 ℃;

Specifically, the following examples are presented to illustrate:

in the insert for hot stamping dies, die forging steel such as Dievar, W360 and Q-grade H13 is widely used in the prior art, and there is a problem that the wear rate is high in the hot stamping environment of non-plated plates. According to Table 1, the powder system HS-P improves the C content to 0.70-0.80% and the Cr content to 7.00-8.00% on the basis of H13 die steel, so as to improve the wear resistance of the material and solve the problem that the R angle of the insert of the hot stamping die is easy to wear. Meanwhile, a layer of high-performance powder HS-P is clad on the low-cost base material HS-S through laser cladding, so that the structure non-segregation and high fatigue performance of the clad alloy layer HS-P are 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

1. The preparation process comprises the following steps:

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

3) And (3) processing a base material: cutting and cutting the base material to 2.5mm according to the product profile. See fig. 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: 2 layers are clad on the surface of the substrate, the single-layer thickness is controlled to be 1.6mm, the pass lap ratio is controlled to be 30-40%, and the laser power is 2KW. See fig. 3-4 (c).

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

7) And (3) product finishing: and (3) taking the product profile as a reference, cutting and reducing the material by taking the area (1.6x2-2.5=0.7 mm) of the cladding layer higher than the profile area, and finishing the preparation of the die insert. See fig. 3-4 (d).

2. Tissue and performance comparison

The following is in comparison with the hot stamping usual material Q grade H13. 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 subjected to vacuum melting, electroslag remelting, multidirectional forging and other processes. Generally, the microstructure characteristics of H13 die steel are characterized by macrosegregation bands that are not eliminated during tempering and coarse grains are present as matrix grain size distribution is uneven. FIG. 5 shows the cladding layer structure of the HS product of the die steel of the invention, which is finer and has no macrosegregation band therein, although a small amount of void defects exist.

The comparison of actual service of hot stamping shows that the HS die steel failure mode of the invention is mainly abrasion and has no integral cracking phenomenon. 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 being subjected to unstable loading force; and cracks generated by H13 die steel can extend to a waterway, so that the die insert leaks water and is scrapped early. In addition, the present invention HS die steel product maintains the profile temperature at 100-120 ℃ and the H13 die steel maintains the profile temperature at 110-135 ℃ during continuous production, which also demonstrates that the present invention HS die steel has better heat conduction properties. The specific results are shown in the following table:

table: the invention is compared with the performance of similar die steel products

The above-described embodiments are merely illustrative of the principles of the present application and their effectiveness, and are not intended to limit the present application. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the present application. Accordingly, it is intended that all equivalent modifications and variations which may be accomplished by those skilled in the art without departing from the spirit and technical spirit of the present invention 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 matrix which are arranged up and down; the thickness of the cladding layer is 1-10mm, and the hardness is 52-62HRC; the thickness of the matrix is 40-400mm, the hardness is 30-45HRC, a waterway is arranged in the matrix, the diameter of the waterway is 5-15mm, and the distance between the waterway and the molded surface of the product is 5-20mm; an intermediate layer is arranged on the cladding layer, and the intermediate layer is positioned at the transition between the cladding layer and the substrate; the matrix comprises the following components: 0.35-0.40% of C, 0.60-1.00% of Mn, 0.40-0.60% of Si, 1.40-2.00% of Cr, 0.30-0.60% of Mo, 0.10-0.30% of V, and the balance of Fe and impurities; the cladding layer comprises the following components: 0.70-0.80% of C, 0.40-0.60% of Mn, 0.60-0.80% of Si, 7.00-8.00% of Cr, 1.00-1.50% of Mo, 2.50-3.00% of V, and the balance of Fe and impurities.

2. Additive manufacturing process for hot stamped high wear resistant die steel product according to claim 1, characterized by the following steps: s1: and (3) processing a base material: performing material reduction processing on the profile of the base material by taking the profile of the die steel product as a reference, wherein the over-cutting amount of the profile of the base material is 0.1-5mm; 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 characteristic of cladding powder, controlling the pass lap ratio to be 25-50%, controlling the laser power to be 1-6kw, controlling the diameter of a light spot to be 0.2-3mm, cladding 1-4 alloy layers on the surface of the base material, controlling the thickness of a single alloy layer to be 0.1-3mm, and controlling the total thickness of cladding layers formed by the plurality of alloy layers to be higher than the over-cutting amount of the base material by 0.2-2mm; s3: tempering the product: tempering the die steel product at 450-600 ℃ for 1-3 times; s4: and (3) product finishing: and taking the molded surface of the product as a reference, and performing material reduction processing on the area of the product cladding layer higher than the molded surface to obtain a finished product.

3. Additive manufacturing process for hot stamped high wear resistant die steel product according to claim 2, characterized in that: 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 ℃.

4. An additive manufacturing process for hot stamped high wear resistant die steel product according to claim 3, characterized by: when preheating the article substrate, the heating temperature is 300-450 ℃.

5. An additive manufacturing process for hot stamped high wear resistant die steel product according to claim 3, characterized by: when the product substrate is heated in-line, the heating temperature is 250-400 ℃.