High plasticity high strength die steel and its preparation process

Abstract

This invention discloses a high-plasticity, high-strength mold steel alloy powder for SLM (Sequencing Molding Machine) processes. Its composition, by weight percentage, includes: C 0.09-0.13%, Mn 0.05-0.2%, Cr 12.1-12.6%, Ni 13.0-15.2%, Mo 0.7-1.0%, Al 0.8-1.0%, B 0.002-0.004%, Si 0.1-0.15%, and Ti, with the balance being Fe; wherein the Ti / (Si+B) ratio is 0.7-0.8. This invention also discloses a preparation process for the high-plasticity, high-strength mold steel. By adjusting the contents of Ti, B, and other elements, and selecting a Ti / (Si+B) ratio of 0.7-0.8, combined with a suitable preparation process, this invention refines the grains and increases hardenability, ultimately obtaining a high-plasticity, high-strength mold steel.

Description

A high-plasticity, high-strength mold steel and its preparation process Technical Field

[0001] This invention relates to the field of additive manufacturing alloys, and more particularly to a high-plasticity, high-strength mold steel and its preparation process. Background Technology

[0002] CORRAX stainless steel possesses excellent corrosion resistance, high hardness, and superior mechanical strength, making it a preferred material for injection molding tools and extrusion dies for corrosive plastics and rubber. The chemical composition of CORRAX stainless steel by weight is: C 0.03%, Si 0.3%, Mn 0.3%, Cr 12.0%, Ni 9.2%, Mo 1.4%, Al 1.6%, with the balance being Fe. It can be seen that this stainless steel contains a high content of Cr and Ni. The synergistic effect of these two elements at high contents gives the stainless steel excellent corrosion resistance; however, the high Cr content also reduces the plasticity of the stainless steel. Due to the diverse shapes of rubber products, traditional casting processes cannot produce CORRAX stainless steel into mold steels with complex shapes.

[0003] Traditional mold steel manufacturing involves numerous complex processes and is time-consuming. Additive manufacturing, however, is different; computer-controlled printing can create three-dimensional objects of any shape. Selective laser melting (SLM), a major technique in additive manufacturing, involves using specialized software to slice and layer a CAD 3D model into two-dimensional cross-sectional views and plan the scanning path. Then, a scraper evenly spreads powder onto the laser processing area. The computer controls the laser beam via a scanning galvanometer to selectively melt the metal powder, layer by layer, creating a three-dimensional entity identical to the model. This process is highly precise and fast.

[0004] Therefore, SLM (Surface Mount Technology) can be used to print CORRAX stainless steel into various shapes of mold steel. However, during the SLM printing process, it was found that the plasticity and strength of CORRAX stainless steel molds printed using this process are significantly reduced. In rubber production, because rubber itself easily expands in volume, this places a large external force on the rubber mold. If the plasticity of the rubber mold is insufficient, cracking is likely to occur. Therefore, how to further improve the plasticity while ensuring excellent strength in CORRAX stainless steel molds has become an urgent problem to be solved. Summary of the Invention

[0005] Based on the technical problems existing in the background art, this invention proposes a high-plasticity, high-strength mold steel and its preparation process. Compared to the chemical composition of CORRAX stainless steel, the alloy powder of this invention maintains a basically unchanged Cr content, adds Ti and B at certain proportions, with a Ti / (Si+B) ratio of 0.7-0.8, and adjusts the content of other elements. Combined with the preparation and processing technology, a high-plasticity, high-strength rubber mold steel is finally obtained.

[0006] A high-plasticity, high-strength mold steel alloy powder for SLM process comprises, by weight percentage: C 0.09-0.13%, Mn 0.05-0.2%, Cr 12.1-12.6%, Ni 13.0-15.2%, Mo 0.7-1.0%, Al 0.8-1.0%, B 0.002-0.004%, Si 0.1-0.15%, and Ti, with the balance being Fe;

[0007] The ratio of Ti / (Si+B) is 0.7-0.8.

[0008] Compared to CORRAX stainless steel, this invention, by adding Ti and B elements, allows Ti to form a Fe-Ni-Ti solid solution within the ferrite with Fe and Ni, which have a higher content proportion, thus enhancing plasticity. The synergy between B and Ti results in finer ferrite size, while the synergy between B and Si improves hardenability during solution quenching and maintains good stability during aging. This results in the formation of hard carbides such as BC and TiC after aging, which are uniformly distributed in small particles, giving the die steel uniform mechanical properties across the entire cross-section, thereby significantly increasing the steel's plasticity and strength. Furthermore, the inventors discovered that a Ti / (Si+Bi) ratio of 0.7-0.8 can improve the alloy's brittleness. At this ratio, the combination of Si, B, and Ti results in a more uniform alloy microstructure during aging, with grains evenly dispersed in the bainite / martensite dual phase, further enhancing strength and plasticity. The present invention also increases the Ni content, which can be combined with Cr to first ensure the corrosion resistance of the alloy. It was also found that a certain amount of Ni can strengthen the ferrite and refine the pearlite of the mold steel of the present invention, thereby further improving the strength of the alloy and having little effect on plasticity.

[0009] Preferably, its composition by weight percentage includes: C 0.10%, Mn 0.1%, Cr 12.4%, Ni 14.2%, Mo 0.9%, Al 0.9%, B 0.003%, Si 0.15%, Ti 0.107%, with the balance being Fe.

[0010] Preferably, the particle size of the alloy powder is 15-53 μm;

[0011] The above particle size refers to the range from the minimum particle size to the maximum particle size.

[0012] More preferably, the D50 of the alloy powder is 30-45 μm.

[0013] If the alloy powder has a uniform particle size distribution and high bulk density, the printed parts will have high density, fewer pores, and better polishing effect.

[0014] Preferably, the loose packing density of the alloy powder is 3.9-4.3 g / cm³. 3 .

[0015] In the SLM process, the loose packing density directly determines the density of the powder layer. When the loose packing density of the powder is low, the gaps between the powder particles in the powder layer become larger, and the connectivity between layers deteriorates, leading to the formation of pores during part forming and a decrease in internal density. Furthermore, a low loose packing density in the powder layer also results in a larger height difference during the solidification shrinkage of the molten metal during forming, a more severe "step effect," larger dimensional deviations, and an increased probability of defects such as cracks and warping during forming.

[0016] Preferably, the flowability of the alloy powder is 19-21.7 s / 50g.

[0017] For SLM (Surface Mount Technology) processes, poor powder flowability can lead to uneven powder distribution and poor powder flatness, thereby increasing internal defects in the printed parts and affecting their mechanical properties.

[0018] The present invention also provides a preparation process for high-plasticity and high-strength mold steel, comprising the following steps: taking the above-mentioned high-plasticity and high-strength mold steel alloy powder for SLM process, and performing laser selective melting to form mold steel.

[0019] Preferably, after laser selective melting and forming, high-plasticity and high-strength mold steel is obtained by solution treatment and aging treatment.

[0020] Preferably, the laser selective melting forming parameters are: laser power 260-300W, scanning rate 850-900mm / s, spacing 0.10-0.15mm, and powder layer thickness 35-50μm.

[0021] Preferably, the solution treatment has a heating rate of 2.5 min / mm; a solution temperature of 890-910℃; a solution holding time of 20-40 min; and an aging treatment temperature of 450-500℃ and an aging holding time of 4-8 h.

[0022] Preferably, after solution treatment and heat preservation, the solution is rapidly cooled to room temperature with water.

[0023] This invention employs rapid heating and short-term holding in the solution treatment process to obtain fine austenitic grains. Grain size is significantly affected by temperature; too low a temperature will cause carbides to nucleate and grow into coarse particles non-uniformly, while too high a temperature will lead to abnormal grain growth due to mechanical obstacles. Grain refinement can improve the yield point, fatigue strength, and plasticity of metallic materials; therefore, finding suitable solution treatment parameters is crucial for the final mechanical properties of the mold.

[0024] By selecting this aging process according to the above formula, the alloy of the present invention can redeprecipitate a strengthening phase with fine and uniform grains, while eliminating residual stress, so that the prepared mold steel has both high strength and high plasticity.

[0025] The present invention also provides a high-plasticity, high-strength mold steel, which is prepared according to the above-mentioned preparation process of the high-plasticity, high-strength mold steel.

[0026] Beneficial effects:

[0027] This invention improves plasticity and strength by increasing the content of Ti and B to a certain level, with the Ti / (Si+B) ratio being 0.7-0.8, and by appropriately adjusting and optimizing the content of other elements to make them work together, refining the grains and increasing hardenability. Furthermore, by designing appropriate laser selective melting process parameters and solid solution and aging parameters, a high-plasticity and high-strength mold steel is finally prepared. Attached Figure Description

[0028] Figure 1 shows SEM images of the alloy powder for SLM in Example 3 at 200x and 500x magnification, where a is 200x and b is 500x.

[0029] Figure 2 shows the actual rubber mold after additive manufacturing, solution treatment, and aging in Example 3.

[0030] Figure 3 is a metallographic image of the rubber mold after polishing in Example 3. Detailed Implementation

[0031] The technical solution of the present invention will now be described in detail through specific embodiments.

[0032] The following are the laser additive manufacturing printer and performance testing equipment used in the examples:

[0033] The printer uses the HIT-M150 laser selective melting molding machine, a 3D printing mold special machine manufactured by Hart 3D.

[0034] Tensile properties were tested using an AGXplus electronic universal testing machine with a 20Kn specification manufactured by Tsushima, strictly in accordance with the national standard GB / T228-2002 "Metallic Materials - Indoor Tensile Testing Method".

[0035] The hardness test was conducted using an HVS-1000A hardness tester, in accordance with the standard GB / T230 Rockwell Hardness Test for Metallic Materials.

[0036] The performance of the powder was tested using a Mastersizer 3000E powder particle size analyzer and a BT-1001 intelligent powder comprehensive property tester.

[0037] Example 1

[0038] A high-plasticity, high-strength mold steel alloy powder for SLM process comprises, by weight percentage: C 0.09%, Mn 0.05%, Cr 12.6%, Ni 15.2%, Mo 0.7%, Al 1.0%, B 0.002%, Si 0.12%, Ti 0.09%, with the balance being Fe; the Ti / (Si+B) ratio is 0.74.

[0039] After being prepared by Anhui Hart 3D's atomization powder preparation equipment, the alloy powder has a particle size of 15-53μm, a D50 of 30μm, and a loose packing density of 4.3g / cm³. 3 The fluidity is 19s / 50g.

[0040] A process for preparing a high-plasticity, high-strength mold steel includes the following steps:

[0041] The above-mentioned SLM process uses high-plasticity, high-strength mold steel alloy powder to print the mold using a 3D printing mold special machine. The entire molding process is carried out in the sealed molding chamber of the system, and argon gas with a purity of 99.9% is continuously introduced for protection. The laser power of the SLM molding process is adjusted to 260W, the scanning speed to 850mm / s, the scanning interval to 0.10mm, and the powder thickness to 35μm. The molded sample is obtained by SLM molding.

[0042] The molded sample obtained above was heated to 890℃ at a heating rate of 2.5 min / mm, and held at that temperature for 40 min. Then it was quenched in water and rapidly cooled to room temperature. The sample was then heated to 450℃ for aging treatment and held at that temperature for 8 h. Finally, it was air-cooled to room temperature to obtain high-plasticity and high-strength mold steel.

[0043] Example 2

[0044] A high-plasticity, high-strength mold steel alloy powder for SLM process comprises, by weight percentage: C 0.13%, Mn 0.2%, Cr 12.1%, Ni 13.0%, Mo 1.0%, Al 0.8%, B 0.004%, Si 0.1%, Ti 0.083%, with the balance being Fe; the Ti / (Si+B) ratio is 0.8.

[0045] After being prepared by Anhui Hart 3D's atomization powder preparation equipment, the alloy powder has a particle size of 15-53μm, a D50 of 45μm, and a loose packing density of 3.9g / cm³. 3 The fluidity is 21.7s / 50g.

[0046] A process for preparing a high-plasticity, high-strength mold steel includes the following steps:

[0047] The above-mentioned SLM process uses high-plasticity, high-strength mold steel alloy powder to print the mold using a 3D printing mold special machine. The entire molding process is carried out in the sealed molding chamber of the system, and argon gas with a purity of 99.9% is continuously introduced for protection. The laser power of the SLM molding process is adjusted to 300W, the scanning speed to 900mm / s, the scanning interval to 0.15mm, and the powder thickness to 50μm. The molded sample is obtained by SLM molding.

[0048] The molded sample obtained above was heated to 910℃ at a heating rate of 2.5 min / mm, and held at that temperature for 20 min. Then it was quenched in water and rapidly cooled to room temperature. The sample was then heated to 500℃ for aging treatment and held at that temperature for 4 h. Finally, it was air-cooled to room temperature to obtain high-plasticity and high-strength mold steel.

[0049] Example 3

[0050] A high-plasticity, high-strength mold steel alloy powder for SLM process comprises, by weight percentage: C 0.10%, Mn 0.1%, Cr 12.4%, Ni 14.2%, Mo 0.9%, Al 0.9%, B 0.003%, Si 0.15%, Ti 0.107%, with the balance being Fe; the Ti / (Si+B) ratio is 0.7.

[0051] After being prepared by Anhui Hart 3D's atomization powder preparation equipment, the alloy powder has a particle size of 15-53μm, a D50 of 35.6μm, and a loose packing density of 4.11g / cm³. 3 The fluidity is 20.35s / 50g.

[0052] A process for preparing a high-plasticity, high-strength mold steel includes the following steps:

[0053] The above-mentioned SLM process uses high-plasticity, high-strength mold steel alloy powder to print the mold using a 3D printing mold special machine. The entire molding process is carried out in the sealed molding chamber of the system, and argon gas with a purity of 99.9% is continuously introduced for protection. The laser power of the SLM molding process is adjusted to 280W, the scanning speed to 880mm / s, the scanning spacing to 0.13mm, and the powder thickness to 40μm. The molded sample is obtained by SLM molding.

[0054] The molded sample obtained above was heated to 900℃ at a heating rate of 2.5 min / mm, and held at that temperature for 30 min. Then it was quenched in water and rapidly cooled to room temperature. The sample was then heated to 480℃ for aging treatment and held at that temperature for 6 h. Finally, it was air-cooled to room temperature to obtain high-plasticity and high-strength mold steel.

[0055] Figure 1 shows scanning electron microscope images of the alloy powder for SLM in Example 3 at 200x (a) and 500x (b). As can be seen from Figure 1, the powder prepared after atomization has good sphericity, uniform particle size distribution, and smooth surface.

[0056] Figure 2 shows the physical image of the rubber mold after additive manufacturing, solution treatment, and aging in Example 3. This confirms the feasibility of using the alloy powder of the present invention to prepare complex rubber molds through additive manufacturing and subsequent processing.

[0057] Figure 3 is a metallographic image of the rubber mold after polishing in Example 3. The image shows that the surface of the rubber mold has no obvious cracks or porosity defects, and the quality is good.

[0058] Comparative Example 1

[0059] The CORRAX stainless steel was prepared according to the following chemical composition by weight: C 0.03%, Si 0.3%, Mn 0.3%, Cr 12.0%, Ni 9.2%, Mo 1.4%, Al 1.6%, with the balance being Fe. Raw materials were added, and alloy powder was prepared using an atomization powder preparation device manufactured by Anhui Hart 3D. Subsequent operating steps and parameters were consistent with those in Example 3, resulting in CORRAX mold steel.

[0060] Comparative Example 2

[0061] The mold steel alloy powder used in this comparative example comprises, by weight percentage: C 0.10%, Mn 0.1%, Cr 12.4%, Ni 14.2%, Mo 0.9%, Al 0.9%, B 0.003%, Si 0.15%, Ti 0.153%, with the balance being Fe. That is, the Ti / (Si+B) ratio in this comparative example is 1. The remaining operating steps and parameters are consistent with those in Example 3, resulting in the mold steel.

[0062] Comparative Example 3

[0063] The mold steel alloy powder used in this comparative example comprises, by weight percentage: C 0.10%, Mn 0.1%, Cr 12.4%, Ni 14.2%, Mo 0.9%, Al 0.9%, B 0.003%, Si 0.15%, Ti 0.06%, with the balance being Fe. That is, the Ti / (Si+B) ratio in this comparative example is 0.39. The remaining operating steps and parameters are consistent with those in Example 3, resulting in the mold steel.

[0064] Comparative Example 4

[0065] The only difference between this comparative example and Example 3 is that the aging treatment temperature is 400℃. The other operating steps and parameters are the same as those in Example 3, and mold steel is obtained.

[0066] Comparative Example 5

[0067] The only difference between this comparative example and Example 3 is the aging treatment temperature of 530℃. The other operating steps and parameters are the same as those in Example 3, and mold steel is obtained.

[0068] The following are the mechanical properties of the mold obtained from the examples and comparative examples. The performance test results are shown in Table 1.

[0069] Table 1. Performance test results of mold steel in embodiments and comparative examples of the present invention.

[0070]

[0071]

[0072] The test results above show that by increasing the proportion of Ti and B, with a Ti / (Si+B) ratio of 0.7-0.8, this invention, compared to the CORRAX mold steel in Comparative Example 1, not only maintains the same hardness and strength but also significantly improves the elongation, indicating an increase in the steel's plasticity. A Ti / (Si+B) ratio that is too high results in a large proportion of carbides, leading to a certain increase in strength but a significant decrease in plasticity; a Ti / (Si+B) ratio that is too low results in a less pronounced refining effect and a smaller improvement in plasticity. The strength of the mold steel first increases and then decreases with increasing aging temperature. The data from Comparative Examples 2-5 confirm that adding specific proportions of Ti, Si, and B, combined with appropriate heat treatment processes, is necessary to achieve the high plasticity and high strength of the final rubber mold.

[0073] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-plasticity, high-strength mold steel alloy powder for SLM process, characterized in that, Its composition by weight percentage includes: C 0.09-0.13%, Mn 0.05-0.2%, Cr 12.1-12.6%, Ni 13.0-15.2%, Mo 0.7-1.0%, Al 0.8-1.0%, B 0.002-0.004%, Si 0.1-0.15% and Ti, with the balance being Fe; wherein the ratio of Ti / (Si+B) is 0.7-0.

8.

2. The high-plasticity, high-strength mold steel alloy powder for SLM process according to claim 1, characterized in that, Its composition by weight percentage includes: C 0.10%, Mn 0.1%, Cr 12.4%, Ni 14.2%, Mo 0.9%, Al 0.9%, B 0.003%, Si 0.15%, Ti 0.107%, with the balance being Fe.

3. The high-plasticity, high-strength mold steel alloy powder for SLM process according to claim 1 or 2, characterized in that, The particle size of the alloy powder is 15-53 μm; the D50 of the alloy powder is 30-45 μm.

4. The high-plasticity, high-strength mold steel alloy powder for SLM process according to claim 1 or 2, characterized in that, The loose packing density of the alloy powder is 3.9-4.3 g / cm³. 3 .

5. The high-plasticity, high-strength mold steel alloy powder for SLM process according to claim 1 or 2, characterized in that, The flowability of the alloy powder is 19-21.7 s / 50g.

6. A preparation process for a high-plasticity, high-strength mold steel, characterized in that, The process includes the following steps: taking high-plasticity, high-strength mold steel alloy powder for SLM process as described in any one of claims 1-5, and performing selective laser melting to form mold steel.

7. The preparation process of the high-plasticity, high-strength mold steel according to claim 6, characterized in that, After laser selective melting and forming, high-plasticity and high-strength mold steel is obtained through solution treatment and aging treatment.

8. The preparation process of the high-plasticity, high-strength mold steel according to claim 6 or 7, characterized in that, The specific parameters for laser selective melting and forming are: laser power 260-300W, scanning rate 850-900mm / s, spacing 0.10-0.15mm, and powder layer thickness 35-50μm.

9. The preparation process of the high-plasticity, high-strength mold steel according to claim 7, characterized in that, The solution treatment has a heating rate of 2.5 min / mm, a solution temperature of 890-910℃, and a solution holding time of 20-40 min. The aging treatment has a temperature of 450-500℃ and an aging holding time of 4-8 h.

10. A high-plasticity, high-strength mold steel, characterized in that, It is prepared according to the preparation process of the high-plasticity and high-strength mold steel according to any one of claims 6-9.

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