CN116288054A - Stress cracking resistant medium-low carbon 3D printing die steel and heat treatment method thereof - Google Patents

Abstract

The invention relates to a stress cracking resistant medium-low carbon 3D printing die steel and a heat treatment method thereof, and belongs to the technical field of 3D printing. The die steel material comprises 0.1-0.6wt% of carbon element, 5.0-15.0wt% of chromium element, 1.0-5.0wt% of nickel element, 0-3.0wt% of molybdenum element, 0-1.0wt% of vanadium element, 0-1.0wt% of niobium element, 0-1.0wt% of titanium element, 0-1.0wt% of zirconium element and the balance of iron element, wherein the material contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium. The mass percentage of carbon atoms dissolved in the matrix is less than 0.2wt% by adjusting the types and the proportions of the strong carbide forming elements, so that the residual stress is reduced, and the large-size part is printed without stress cracking. And then the hardness, strength, toughness, wear resistance and service life of the die steel are improved through multi-step heat treatment.

Description

Stress cracking resistant medium-low carbon 3D printing die steel and heat treatment method thereof

Technical Field

The invention relates to a stress cracking resistant medium-low carbon 3D printing die steel and a heat treatment method thereof, and belongs to the technical field of 3D printing.

Background

The 3D printing is a technology for finally obtaining a solid structure by stacking materials layer by layer through an automatic control system based on a three-dimensional model of a part and through data processing, and has the characteristics of short production period, high material utilization rate, no limitation of a space structure and the like, and is widely paid attention in recent years. The selective laser melting technology (SLM) is used for melting and forming metal powder by laser, has application to the die industry on a certain scale, provides a solution for die manufacturing with a complex structure, and simultaneously enables the die to be more convenient and efficient in the production and manufacturing process. Based on the characteristics of the 3D printing layer-by-layer manufacturing, when the SLM technology is used for manufacturing, heat distribution difference exists at each part of the part, so that the cooling shrinkage degree is uneven, macroscopic stress is generated, and macroscopic stress cracking is even caused at stress concentration positions such as part corners. With the industrial upgrade of the mold industry, the efficient manufacture of mold products with complex structures by using a precision technology has become a new development trend. Among these, the rational choice of printing materials is the fundamental approach to solve SLM stress cracking, improve manufacturing efficiency and obtain high performance mold products. At present, if the SLM technology is used for melting and molding the traditional medium and low carbon die steel (such as S136, H13 and the like), although the material has the advantages of high hardness, good wear resistance, low cost and the like, the carbon-containing martensitic structure formed by the material in the printing process can greatly increase the hardness and brittleness of the printed part, the increase of residual stress tends to induce macroscopic stress cracking when manufacturing parts of larger size (300 x 300 mm) or more complex structure, and thus cannot meet the requirements of actual production and manufacture. Existing 3D printing die steel materials (such as 18Ni300, corrax and the like) are carbon-free or ultralow-carbon precipitation hardening steel or maraging steel, and although the structural size of the 3D printing die steel materials can be unrestricted, the materials lack strengthening effect of internal carbide, so that poor wear resistance is caused, and the service life of a die is severely limited; and the material has high content of alloy elements such as nickel, molybdenum, cobalt and the like, and high material cost, and severely restricts the application of the material in the field of 3D printing dies. Therefore, there is a need in the art to develop a stress crack resistant medium and low carbon 3D printing die steel.

Disclosure of Invention

The invention aims to solve the technical problem of how to obtain a middle-low carbon 3D printing die steel with stress cracking resistance; and how to solve the problems of macroscopic stress cracking of the existing 3D printing medium-low carbon die steel, poor wear resistance of the existing 3D printing die material, high cost and the like.

In order to solve the problems, the technical scheme adopted by the invention is to provide the stress cracking resistant medium-low carbon 3D printing die steel, which comprises the following elements in percentage by mass: 0.1-0.6wt% of carbon element, 5.0-15.0wt% of chromium element, 1.0-5.0wt% of nickel element, 0-3.0wt% of molybdenum element, 0-1.0wt% of vanadium element, 0-1.0wt% of niobium element, 0-1.0wt% of titanium element, 0-1.0wt% of zirconium element and the balance of iron element, wherein the total mass percentage of the elements is 100wt%.

Preferably, the die steel contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium; the mass percentage of carbon atoms dissolved in the matrix is less than or equal to 0.2wt% by adjusting the types and the proportions of the strong carbide forming elements.

Preferably, the die steel contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium; by adjusting the types and the proportions of the strong carbide forming elements, the content of the alloy elements is ensured, and meanwhile, the formula (1) is also required to be satisfied:

the invention provides a stress cracking resistant medium-low carbon 3D printing die steel, which comprises the following elements in percentage by mass: 0.2-0.4wt% of carbon element, 5.0-15.0wt% of chromium element, 1.0-3.5wt% of nickel element, 1.0-2.0wt% of molybdenum element, 0-0.5wt% of vanadium element, 0-0.5wt% of niobium element, 0-0.8wt% of titanium element, 0-0.5wt% of zirconium element and the balance of iron element, wherein the total mass percentage of the elements is 100wt%.

Preferably, the die steel contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium; the mass percentage of carbon atoms dissolved in the matrix is less than or equal to 0.15wt% by adjusting the types and the proportions of the strong carbide forming elements.

Preferably, the die steel contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium; by adjusting the types and the proportions of the strong carbide forming elements, the content of the alloy elements is ensured, and meanwhile, the formula (2) is required to be satisfied:

the invention provides a heat treatment method of a stress cracking resistant medium-low carbon 3D printing die steel, which comprises the following steps:

step 1: printing and molding a 3D printing die steel powder material resistant to stress cracking, and then loading the molded steel powder material into a heating furnace;

step 2: heating the heating furnace to 800-850 ℃ for first-stage heat treatment, and preserving heat for 5min to enable the surface temperature and the internal temperature of the part to be consistent; then heating the heating furnace to 950-1100 ℃ slowly to perform second-stage heat treatment, and preserving the heat for 30-60min to enable the internal tissues to be completely austenitized;

step 3: immediately taking out the die steel after heat preservation, and then cooling by air cooling, air cooling or oil cooling quenching;

step 4: tempering the die steel cooled to room temperature after quenching at 450-600 ℃ for 2-3 hours, and naturally cooling to room temperature in air after tempering;

step 5: and (3) repeating the operation of the step (4) for 2-3 times, namely finishing the heat treatment process of the die steel, and obtaining the final hardness, toughness and wear resistance.

Compared with the prior art, the invention has the following beneficial effects:

1. according to the invention, through innovative component design, strong carbide forming elements of vanadium, niobium, titanium and zirconium are added into the medium-low carbon 3D printing die steel, the carbon content of solid solution in a martensitic matrix is reduced in a carbide precipitation mode, the martensitic hardness is reduced, and the plasticity and toughness of martensite are improved by adjusting the content of nickel element, so that the medium-low carbon die steel capable of safely printing 300mm in size and resisting stress cracking is obtained;

2. compared with the traditional heat treatment of 3D printing die steel, the method uses high complete austenitizing temperature, better eliminates anisotropy and component segregation, and simultaneously utilizes stable strong carbide pinning austenite grain boundaries formed in the printing process to finally obtain the quenched martensitic structure with high hardness and high toughness.

Drawings

FIG. 1 is a longitudinal section optical microscope image of a printing tissue for 3D printing by using the die steel provided by the invention;

FIG. 2 is a longitudinal section scanning electron microscope image of a printing structure for 3D printing by using the die steel provided by the invention;

FIG. 3 is a longitudinal section optical microscope image of a die steel after heat treatment using the present invention;

fig. 4 is a longitudinal section scanning electron microscope image of a mold steel heat treated by the present invention.

Detailed Description

In order to make the invention more comprehensible, preferred embodiments accompanied with the accompanying drawings are described in detail as follows:

as shown in fig. 1-4, the technical scheme adopted by the invention is to provide a stress cracking resistant medium-low carbon 3D printing die steel material, which comprises the following components: 0.1-0.6wt% of carbon element, 5.0-15.0wt% of chromium element, 1.0-5.0wt% of nickel element, 0-3.0wt% of molybdenum element, 0-1.0wt% of vanadium element, 0-1.0wt% of niobium element, 0-1.0wt% of titanium element, 0-1.0wt% of zirconium element and the balance of iron element, wherein the total mass percentage of the above elements is 100wt%; while ensuring the content of the alloy elements, the formula (1) needs to be satisfied:

the invention provides a stress cracking resistant 3D printing die steel material, which comprises the following components: 0.2-0.4wt% of carbon element, 5.0-15.0wt% of chromium element, 1.0-3.5wt% of nickel element, 1.0-2.0wt% of molybdenum element, 0-0.5wt% of vanadium element, 0-0.5wt% of niobium element, 0-0.8wt% of titanium element, 0-0.5wt% of zirconium element and the balance of iron element, wherein the total mass percentage of the elements is 100wt%; while ensuring the content of the alloy elements, the formula (2) needs to be satisfied:

the material contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium, after the SLM process is used for melting the carbon-containing metal powder material, carbon atoms are preferentially combined with the carbon-containing metal powder material to form extremely stable MC-type carbide before martensitic transformation occurs, so that the content of solid-solution carbon atoms in an austenite matrix is obviously reduced, the carbon content in martensite after cooling is further reduced, the hardness of the martensite matrix is obviously reduced, and the residual stress is reduced. When the hardness after printing is less than 45HRC, the macroscopic stress cracking tendency of the part will be greatly reduced, and therefore the residual carbon content in the matrix after precipitation of strong carbides should be less than 0.15wt%. In addition, the reduction of the carbon content of the solid solution in the matrix also reduces the twin structure in the substructure of the medium-low carbon martensite, improves the toughness and plasticity of the martensite structure, and enhances the crack initiation and propagation resistance of the martensite structure.

The carbon content of the martensitic matrix is controlled through comprehensive adjustment of the contents of vanadium element, niobium element, titanium element and zirconium element, so that the printing hardness of the part is maintained in a reasonable range, and the stress cracking tendency of the part is reduced; in addition, the strong carbide formed by the four elements can pin grain boundaries, delay the grain growth phenomenon in printing and subsequent heat treatment processes, and improve the toughness of the 3D printing die steel. The nickel element is controlled within the range of 1.0-5.0wt%, and if the nickel element is less than 1.0wt%, the nickel element cannot provide enough toughness and plasticity for a martensitic matrix, so that the cracking resistance of the material is reduced; if it exceeds 5.0wt%, austenite is strongly stabilized, resulting in insufficient hardness after quenching. The carbon element is controlled within the range of 0.1-0.6wt%, and if the carbon element is less than 0.1wt%, the strength and the wear resistance of the die steel in the use process cannot be met; if it is higher than 0.6wt%, a large amount of strong carbide is precipitated during 3D printing, and the hardness and brittleness of the printed part are remarkably increased. The chromium element is required to be controlled within the range of 5.0-15.0wt%, and if the chromium element is less than 5wt%, the chromium element cannot provide enough hardenability for the steel; if the weight is higher than 15wt%, high-temperature ferrite structure is easy to exist, and the usability of the 3D printing die steel is affected. The addition of a proper amount of molybdenum element can increase the tempering stability of the steel and improve the strength and the wear resistance.

The stress cracking resistant 3D printing die steel material has lower hardness after printing and forming, has a certain degree of anisotropy and needs further treatment to meet the end use requirement.

In order to obtain good service performance of the stress cracking resistant 3D printing die steel, the invention also provides a heat treatment method, which comprises the following process steps:

step 1: printing and molding the stress cracking resistant 3D printing die steel material, and then loading the molded material into a heating furnace, wherein the temperature of the heating furnace is less than 200 ℃;

step 2: heating the heating furnace to 800-850 ℃ for first-stage heat treatment, and preserving heat for 5min to enable the surface temperature and the internal temperature of the part to be consistent; then heating the heating furnace to 950-1100 ℃ slowly to perform second-stage heat treatment, and preserving the heat for 30-60min to enable the internal tissues to be completely austenitized;

step 3: immediately taking out the die steel after heat preservation, and then cooling by air cooling, air cooling or oil cooling quenching;

step 4: tempering the die steel cooled to room temperature after quenching at 450-600 ℃ for 2-3 hours, and naturally cooling to room temperature in air after tempering;

step 5: and (3) repeating the operation of the step (4) for 2-3 times, namely finishing the heat treatment process of the die steel, and obtaining the final hardness, toughness and wear resistance.

Compared with the traditional 3D printing die steel, the higher complete austenitizing temperature is more favorable for thoroughly eliminating the anisotropy of the 3D printing structure, and can also eliminate the component segregation of the 3D printing structure to a greater extent so as to improve the toughness. In addition, since a large amount of fine and dispersed strong carbides of one or more of vanadium, niobium, titanium and zirconium are generated in the SLM processing process, the type of carbides has extremely strong stability, are not dissolved in austenite during high-temperature quenching, and can not be grown up due to pinning of austenite grain boundaries, so that the die steel still has high hardness after high-temperature quenching. The die steel has good service performance after tempering, the hardness is more than 50HRC, the tensile strength is more than 1600MPa, the yield strength is more than 1150MPa, the Charpy V-shaped notch impact toughness is more than 50J, and the wear resistance is equivalent to H13 of the traditional die steel.

Example 1

A stress cracking resistant medium-low carbon 3D printing die steel comprises the following components: 0.22wt% of carbon element, 11.5wt% of chromium element, 2.0wt% of nickel element, 1.0wt% of molybdenum element, 0.2wt% of vanadium element, 0wt% of niobium element, 0.2wt% of titanium element, 0wt% of zirconium element and the balance of iron element, wherein the sum of the mass percentages of the above elements is 100wt%. The content of solid solution carbon in the matrix after the precipitation of the strong carbide is 0.12 weight percent; the molten pool structure after printing is more evenly distributed martensite, retained austenite and strong carbide, as shown in figure 1.

The heat treatment process after printing is as follows: heating to 825 ℃, preserving heat for 5min, slowly heating to 1020 ℃, preserving heat for 30min, taking out after heat preservation is finished, and cooling by air; and then tempering twice after heating to 500 ℃.

The printed 250-250 size has no macroscopic stress cracking, the printed hardness is 40HRC, the heat-treated hardness is 50.5HRC, the tensile strength is 1738MPa, the yield strength is 1248MPa, and the impact toughness is Akv 48.3J.

Example 2

A stress cracking resistant medium-low carbon 3D printing die steel comprises the following components: 0.30wt% of carbon element, 5.50wt% of chromium element, 3.0wt% of nickel element, 1.5wt% of molybdenum element, 0.3wt% of vanadium element, 0.1wt% of niobium element, 0.3wt% of titanium element, 0.1wt% of zirconium element and the balance of iron element, wherein the sum of the mass percentages of the above elements is 100wt%. The content of solid-solution carbon in the matrix after precipitation of the strong carbide was 0.128wt%.

The heat treatment process after printing is as follows: heating to 850 ℃ and preserving heat for 5min, then slowly heating to 1080 ℃ and preserving heat for 30min, taking out after heat preservation is finished, and cooling with air; and then tempering twice after heating to 540 ℃.

The printed 250-250 size has no macroscopic stress cracking, the printed hardness is 42HRC, the heat-treated hardness is 52HRC, the tensile strength is 1833MPa, the yield strength is 1358MPa, and the impact toughness is Akv 37.9J.

Example 3

A stress cracking resistant medium-low carbon 3D printing die steel comprises the following components: 0.38wt% of carbon element, 5.0wt% of chromium element, 3.5wt% of nickel element, 2.0wt% of molybdenum element, 0.3wt% of vanadium element, 0.15wt% of niobium element, 0.5wt% of titanium element, 0.15wt% of zirconium element and the balance of iron element, wherein the sum of the mass percentages of the above elements is 100wt%. The content of solid-solution carbon in the matrix after precipitation of the strong carbide is 0.145wt%.

The heat treatment process after printing is as follows: heating to 850 ℃ for 5min, slowly heating to 1100 ℃ for 30min, taking out after the heat preservation is finished, and cooling by air; and then tempering twice after heating to 550 ℃.

The printed 250-250 size has no macroscopic stress cracking, the printed hardness is 43.5HRC, the heat-treated hardness is 53HRC, the tensile strength is 1868MPa, the yield strength is 1379MPa, and the impact toughness is Akv 32.4J.

While the invention has been described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Equivalent embodiments of the present invention will be apparent to those skilled in the art having the benefit of the teachings disclosed herein, when considered in the light of the foregoing disclosure, and without departing from the spirit and scope of the invention; meanwhile, any equivalent changes, modifications and evolution of the above embodiments according to the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims (7)

1. The medium-low carbon 3D printing die steel resistant to stress cracking is characterized by comprising the following elements in percentage by mass: 0.1-0.6wt% of carbon element, 5.0-15.0wt% of chromium element, 1.0-5.0wt% of nickel element, 0-3.0wt% of molybdenum element, 0-1.0wt% of vanadium element, 0-1.0wt% of niobium element, 0-1.0wt% of titanium element, 0-1.0wt% of zirconium element and the balance of iron element, wherein the total mass percentage of the elements is 100wt%.

2. The stress cracking resistant medium and low carbon 3D printing die steel according to claim 1, wherein the die steel contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium; the mass percentage of carbon atoms dissolved in the matrix is less than or equal to 0.2wt% by adjusting the types and the proportions of the strong carbide forming elements.

3. The stress cracking resistant medium and low carbon 3D printing die steel according to claim 1, wherein the die steel contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium; by adjusting the types and the proportions of the strong carbide forming elements, the content of the alloy elements is ensured, and meanwhile, the formula (1) is also required to be satisfied:

4. the medium-low carbon 3D printing die steel resistant to stress cracking is characterized by comprising the following elements in percentage by mass: 0.2-0.4wt% of carbon element, 5.0-15.0wt% of chromium element, 1.0-3.5wt% of nickel element, 1.0-2.0wt% of molybdenum element, 0-0.5wt% of vanadium element, 0-0.5wt% of niobium element, 0-0.8wt% of titanium element, 0-0.5wt% of zirconium element and the balance of iron element, wherein the total mass percentage of the elements is 100wt%.

5. The stress cracking resistant medium and low carbon 3D printing die steel according to claim 4, wherein the die steel contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium; the mass percentage of carbon atoms dissolved in the matrix is less than or equal to 0.15wt% by adjusting the types and the proportions of the strong carbide forming elements.

6. The stress cracking resistant medium and low carbon 3D printing die steel according to claim 4, wherein the die steel contains one or more strong carbide forming elements of vanadium, niobium, titanium and zirconium; by adjusting the types and the proportions of the strong carbide forming elements, the content of the alloy elements is ensured, and meanwhile, the formula (2) is required to be satisfied:

7. the heat treatment method of the stress cracking resistant medium-low carbon 3D printing die steel is characterized by comprising the following steps of:

step 1: printing and molding a 3D printing die steel powder material resistant to stress cracking, and then loading the molded steel powder material into a heating furnace;

step 2: heating the heating furnace to 800-850 ℃ for first-stage heat treatment, and preserving heat for 5min to enable the surface temperature and the internal temperature of the part to be consistent; then heating the heating furnace to 950-1100 ℃ slowly to perform second-stage heat treatment, and preserving the heat for 30-60min to enable the internal tissues to be completely austenitized;

step 3: immediately taking out the die steel after heat preservation, and then cooling by air cooling, air cooling or oil cooling quenching;

step 4: tempering the die steel cooled to room temperature after quenching at 450-600 ℃ for 2-3 hours, and naturally cooling to room temperature in air after tempering;

step 5: and (3) repeating the operation of the step (4) for 2-3 times, namely finishing the heat treatment process of the die steel, and obtaining the final hardness, toughness and wear resistance.

Images