Composite activated high-hardness non-magnetic steel and preparation method thereof

Abstract

The invention relates to composite activated high-hardness non-magnetic steel and a preparation method thereof, low-manganese low-carbon pre-alloyed powder is used as a matrix, 8-20% by weight of high-manganese high-carbon pre-alloyed powder, 2-4% by weight of graphite powder and 1-2% by weight of copper powder are used as composite activators, and the mass ratio of the high-manganese high-carbon pre-alloyed powder to the graphite powder to the copper powder is (4-10): 2: 1; the composite activated high-hardness non-magnetic steel is obtained from the raw material powder through a powder metallurgy method. The low-carbon and low-manganese alloy serves as a matrix, the high-carbon and high-manganese alloy, the graphite powder and the copper powder serve as the activating agents, the product density is improved, compared with an existing mode that other alloy serves as the activating agents, the situation that the alloy forms a net-shaped structure on the grain boundary can be avoided, the high-hardness non-magnetic steel is obtained, the hardness is 78 HRC or above and is improved by 50% compared with a conventional product, and the density is 7.6 g / cm < 3 > or above.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, specifically relating to a method for preparing composite activated high-hardness non-magnetic steel by pre-alloyed powder compounding technology. Background Technology

[0002] High-manganese non-magnetic steel has a stable austenitic structure at room temperature and a relative permeability of less than 1. Non-magnetic steel has a wide range of applications, including automatic control systems, precision instruments, telecommunications and motors, as well as military applications. With the development of the refrigeration industry, the demand for compressors has increased. The balance weight in compressors plays a crucial role in maintaining the stability of the crankshaft during high-speed rotation. The materials used for balance weights have gradually shifted from high-cost copper-based materials to lower-cost high-manganese steel-based materials, and all materials are required to be non-magnetic or unmagnetized.

[0003] In industry, powder metallurgy is used to prepare high-manganese non-magnetic steel. Powder metallurgy offers advantages such as energy saving and material reduction, suitability for mass production, high product precision, good stability, and excellent performance. Developing powder metallurgy technology for preparing high-manganese non-magnetic steel has a promising market prospect. Currently, powder metallurgy technology is used to mass-produce materials and complex parts that cannot be manufactured using traditional casting and machining methods. Furthermore, powder metallurgy processing avoids the formation of large amounts of carbides, preserving the original physical properties of the non-magnetic steel.

[0004] High-manganese pre-alloyed powders are generally used to address the uneven distribution and easy evaporation of manganese, but this results in poor powder compressibility, making it difficult to obtain high-strength green blanks. Chemical activation sintering with elements such as copper can yield high-density, high-performance powder metallurgy products. However, the addition of conventional chemical elements reduces hardness, and other alloys form a network structure at grain boundaries, reducing product performance risks and failing to meet application requirements.

[0005] Therefore, traditional methods for manufacturing non-magnetic steel cannot meet the requirements for high hardness and high density, and are also costly. There is an urgent need to develop a low-cost, high-density, high-hardness non-magnetic steel powder metallurgy product to meet market demands and drive industry development. Summary of the Invention

[0006] This invention provides a composite activated high-hardness non-magnetic steel and its preparation method, addressing the current technical problems of high cost, low hardness, and low density in high-manganese non-magnetic steel. The obtained composite activated high-hardness non-magnetic steel uses low-carbon and low-manganese as the matrix and high-carbon, high-manganese, graphite powder, and copper powder as activators to increase product density. Compared to existing methods using other alloys as activators, this avoids the formation of a network structure at grain boundaries, which reduces product performance. The developed high-hardness non-magnetic steel has a hardness of over 78 HRC, representing a 50% improvement over conventional products, and a density of 7.6 g / cm³. 3 above.

[0007] In a first aspect, the present invention relates to a composite activated high-hardness non-magnetic steel, which uses raw material powder comprising: a low-manganese, low-carbon pre-alloyed powder as a matrix, and 8-20% by weight of high-manganese, high-carbon pre-alloyed powder, 2-4% by weight of graphite powder, and 1-2% by weight of copper powder as a composite activator, wherein the mass ratio of high-manganese, high-carbon pre-alloyed powder to graphite powder and copper powder is 4-10:2:1; the raw material powder is obtained by powder metallurgy to obtain the composite activated high-hardness non-magnetic steel.

[0008] The low-manganese, low-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 8-11%, C 0.4-0.7%, Si 0.5-0.7%, V 0.5-1.5%, rare earth Y 0.05-0.15%, S≤0.05%, P≤0.1%, O≤0.15%, with the balance being Fe;

[0009] The high-manganese, high-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 25-40%, C 1.5-2.5%, Si 0.5-0.9%, S≤0.05%, P≤0.1%, O≤0.15%, with the balance being Fe.

[0010] Preferably, the low-manganese, low-carbon pre-alloyed powder has a particle size of 110–180 μm;

[0011] Preferably, the high-manganese, high-carbon pre-alloyed powder has a particle size of 40–80 μm;

[0012] Preferably, the graphite powder has a particle size of less than 20 μm; the copper powder has a particle size of 30–40 μm.

[0013] Preferably, the low-manganese, low-carbon pre-alloyed powder has a particle size of 120–150 μm;

[0014] Preferably, the high-manganese, high-carbon pre-alloyed powder has a particle size of 50–70 μm;

[0015] Preferably, the graphite powder has a particle size of 5–15 μm; the copper powder has a particle size of 30–35 μm.

[0016] Secondly, the present invention relates to a method for preparing a composite activated high-hardness non-magnetic steel, wherein the alloy powder green blank is prepared by: thoroughly mixing the raw material powder in a V-type mixer and pressing it into an alloy powder green blank at 550-850 MPa.

[0017] Sintering: The alloy powder green billet is sintered in a mesh belt sintering furnace under a nitrogen and hydrogen mixture atmosphere. The temperature is raised to 350-450 °C and held for 30-40 min, then raised to 700-800 °C and held for 30-40 min, and then raised to 1150-1270 °C and held for 1.5-2.5 h to obtain the composite activated high-hardness non-magnetic steel.

[0018] Preferably, the green body is pressed at 650–750 MPa.

[0019] Preferably, the sintering temperature is raised to 380–430 °C and held for 30–40 min, then raised to 730–780 °C and held for 30–40 min, and then raised to 1170–1240 °C and held for 1.5–2.5 h to obtain the composite activated high-hardness non-magnetic steel.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention uses low-manganese, low-carbon pre-alloyed powder as the matrix, and adds a composite activator, high-manganese, high-carbon pre-alloyed powder, along with graphite powder and copper powder, to achieve composite activation. The low-manganese, low-carbon pre-alloyed powder provides a low-cost matrix, and the Mn content is adjusted to 8-11% and C to 0.4-0.7% to ensure austenitic stability in the product. Simultaneously, the low carbon content inhibits the precipitation of carbides at grain boundaries, ensuring green strength. The high-manganese, high-carbon pre-alloyed powder, through its high carbon content, forms a transient liquid phase, lowering the sintering temperature by 50-100 °C and promoting densification. The addition of Cu powder improves the pressing performance of the pre-alloyed powder; the liquid phase generated during sintering enhances inter-particle diffusion in the matrix, accelerates the densification process, and increases material density. Graphite powder acts as a reducing agent, enhancing lubrication and reducing friction during the pressing process, adjusting the overall carbon content of the non-magnetic steel, and ensuring its high hardness and non-magnetic properties. Compared to existing methods using other alloys as activators, this avoids the formation of a network structure at grain boundaries, which reduces product performance.

[0022] By using a composite activator, high-manganese high-carbon pre-alloy powder, in a mass ratio of 4 to 10:2:1 with graphite powder and copper powder, a good sintering composite activation effect is ensured. With the synergistic effect of high-manganese high-carbon pre-alloy powder, copper powder, and graphite powder, the austenitic phase is formed during the sintering process, ensuring that the steel is non-magnetic and obtaining high hardness and density.

[0023] By effectively combining large particles of low-manganese and low-carbon pre-alloyed powder with high-manganese and high-carbon pre-alloyed powder, copper powder, and graphite powder of different particle sizes, the gaps between particles can be fully filled, the compact density can be increased, the composite activation effect during sintering can be improved, the liquid phase can be obtained quickly, and the density and hardness of non-magnetic steel can be improved.

[0024] In liquid-phase sintering, temperature gradient control has a significant impact on the uniformity of the microstructure. The temperature gradient directly affects the microstructure and properties of the material. Because the raw material powder of this invention uses a multi-particle-size combination, the particle sizes of the matrix powder and the activator differ considerably, easily leading to material deformation due to temperature rise. Controlling the gradient sintering process can prevent material deformation caused by rapid temperature rise during sintering. Holding the sinter at 350–450 °C and 700–800 °C avoids the formation of large temperature gradients, which could increase internal thermal stress and affect the material's density and uniformity. Furthermore, these two temperature rise and holding stages accelerate the formation and diffusion of the liquid phase during the 1150–1270 °C holding sintering process, resulting in a more uniform liquid phase distribution, avoiding component segregation caused by instantaneous high temperatures, improving microstructure uniformity, and thus enhancing the material's density and mechanical properties. The hardness is above 78 HRC, a 50% improvement over conventional products, and the density is 7.6 g / cm³. 3 above. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the preparation process of a composite activated high-hardness non-magnetic steel disclosed in an embodiment of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Traditional methods use a single high-manganese pre-alloyed powder to address the uneven distribution and easy evaporation of manganese, but this results in poor powder compressibility, making it difficult to obtain high-strength green blanks. Adding elements such as copper to form chemically activated sintering can yield high-density, high-performance powder metallurgy products, but the addition of conventional chemical elements reduces hardness, and other alloys form a network structure at grain boundaries, reducing product performance and failing to meet application requirements. Traditional non-magnetic steel manufacturing methods struggle to meet the requirements for high hardness and high density, and are also costly. There is an urgent need to develop a low-cost, high-density, high-hardness non-magnetic steel powder metallurgy product to meet market demands.

[0029] To address the aforementioned technical problems, this invention provides a composite activated high-hardness non-magnetic steel, using raw material powder comprising: a low-manganese, low-carbon pre-alloyed powder as a matrix, and 8-20% by weight of high-manganese, high-carbon pre-alloyed powder, 2-4% by weight of graphite powder, and 1-2% by weight of copper powder as a composite activator. The mass ratio of high-manganese, high-carbon pre-alloyed powder to graphite powder and copper powder is 4-10:2:1. The raw material powder is processed using powder metallurgy to obtain the composite activated high-hardness non-magnetic steel.

[0030] The low-manganese, low-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 8-11%, C 0.4-0.7%, Si 0.5-0.7%, V 0.5-1.5%, rare earth Y 0.05-0.15%, S≤0.05%, P≤0.1%, O≤0.15%, with the balance being Fe;

[0031] The high-manganese, high-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 25-40%, C 1.5-2.5%, Si 0.5-0.9%, S≤0.05%, P≤0.1%, O≤0.15%, with the balance being Fe.

[0032] Carbon is an alloying element that expands the γ-Fe phase region. It is a common alloying element in steel materials and also a frequently used alloying element in powder metallurgy materials. It enhances the matrix strength through interstitial solid solution and, in conjunction with manganese, expands the austenite region. With increasing carbon content, the iron self-diffusion rate increases, promoting the formation and growth of adhesion necks between particles, accelerating material densification, and thus promoting material shrinkage. In low-manganese, low-carbon pre-alloyed powders, C is 0.4–0.7%, while in high-manganese, high-carbon pre-alloyed powders, C is 1.5–2.5%.

[0033] Manganese (Mn) expands the austenite phase region and inhibits the formation of ferromagnetic phases (α-Fe), ensuring the non-magnetic properties of steel. In low-manganese, low-carbon pre-alloyed powders, Mn accounts for 8-11%, while in high-manganese, high-carbon pre-alloyed powders, it accounts for 25-40%. Vanadium can pin austenite grain boundaries and inhibit grain coarsening by forming nanoscale carbonitrides (such as VC and VN). Vanadium carbides are dispersed in the matrix, hindering dislocation movement through the Orowan mechanism, thus improving material hardness and high-temperature strength. In low-manganese, low-carbon pre-alloyed powders, V is preferably 0.5-1.5%.

[0034] In low-manganese, low-carbon pre-alloyed powders containing 0.05–0.15% rare earth Y, rare earth Yttrium can refine grains, improve the purity of the pre-alloyed powder, and also work synergistically with V to reduce oxygen segregation at grain boundaries and improve the hardness of non-magnetic steel.

[0035] Low-manganese, low-carbon pre-alloyed powder provides a low-cost matrix. The lower manganese and carbon content significantly reduces costs while ensuring good pressing and flow properties. Adjusting Mn to 8–11% and C to 0.4–0.7% ensures austenitic stability in the product, while the low carbon content inhibits grain boundary carbide precipitation, ensuring green strength. High-manganese, high-carbon pre-alloyed powder (Mn 20–30%, C 1.9–2.9%) acts as an activator (4–8%), forming a transient liquid phase through its high carbon content, lowering the sintering temperature by 50–100 °C and promoting densification. The high-manganese, high-carbon pre-alloyed powder is added at 8–20% by weight.

[0036] Cu has a low melting point (1083 ℃) and low microhardness. Adding Cu powder can improve the pressing performance of iron-manganese pre-alloyed powder. Furthermore, a liquid phase is generated during sintering, enhancing inter-particle diffusion in the matrix, accelerating the densification process, and increasing the material density. The amount of copper powder added is 1–2% by weight.

[0037] Graphite powder can be used as a reducing agent, providing lubrication and reducing friction during the pressing process. During sintering, it can react with iron to form Fe3C, adjusting the overall carbon content of the non-magnetic steel and ensuring its high hardness. Excessive graphite addition can lead to excessively high steel hardness and cause the non-magnetic steel to become magnetic. The recommended addition weight of graphite powder is 2–4%.

[0038] To obtain high hardness and density in non-magnetic steel and ensure the formation of austenite phase during sintering, thus guaranteeing its non-magnetic nature, a balanced ratio of activator high-manganese high-carbon pre-alloy powder, copper powder, and graphite powder is necessary. A mass ratio of high-manganese high-carbon pre-alloy powder to graphite powder and copper powder of 4–10:2:1 ensures a good sintering composite activation effect, avoids the formation of a network structure at grain boundaries, and, through the synergistic effect of the high-manganese high-carbon pre-alloy powder, copper powder, and graphite powder, ensures the steel is non-magnetic and achieves high hardness.

[0039] In one embodiment, the low-manganese, low-carbon pre-alloyed powder has a particle size of 110–180 μm;

[0040] In one embodiment, the high-manganese, high-carbon pre-alloyed powder has a particle size of 40–80 μm;

[0041] In one embodiment, the graphite powder has a particle size of less than 20 μm; the copper powder has a particle size of 30–40 μm.

[0042] In one embodiment, the low-manganese, low-carbon pre-alloyed powder has a particle size of 120–150 μm;

[0043] In one embodiment, the high-manganese, high-carbon pre-alloyed powder has a particle size of 50–70 μm;

[0044] In one embodiment, the graphite powder has a particle size of 5–15 μm; the copper powder has a particle size of 30–35 μm.

[0045] Low-manganese, low-carbon pre-alloyed powder provides skeletal support for large particles (110–180 μm), ensuring green density and formability. High-manganese, high-carbon pre-alloyed powder (35–45 μm) with fine particles further fills the gaps between large particles and accelerates sintering diffusion. The small particle size provides a high specific surface area, promoting rapid carbon diffusion and austenite homogenization. Small-particle-size copper and graphite powders accelerate liquid phase formation and fill gaps, increasing diffusion rate and improving the density of non-magnetic steel. Graphite powder has a particle size of 5–15 μm; copper powder has a particle size of 30–35 μm.

[0046] By effectively combining low-manganese and low-carbon pre-alloyed powder with large particles of high-manganese and high-carbon pre-alloyed powder, copper powder, and graphite powder of different particle sizes, the gaps between particles can be fully filled, the density of the pressed blank can be increased, the composite activation effect of the sintering process can be improved, the liquid phase can be obtained quickly, and the density and hardness of non-magnetic steel can be improved.

[0047] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing composite activated high-hardness non-magnetic steel, wherein the alloy powder green blank is prepared by: thoroughly mixing the raw material powder in a V-type mixer and pressing it into an alloy powder green blank at 550-850 MPa.

[0048] Sintering: The alloy powder green billet is sintered in a mesh belt sintering furnace under a nitrogen and hydrogen mixture atmosphere. The temperature is raised to 350-450 °C and held for 30-40 min, then raised to 700-800 °C and held for 30-40 min, and then raised to 1150-1270 °C and held for 1.5-2.5 h to obtain the composite activated high-hardness non-magnetic steel.

[0049] The pressing pressure is 550-850 MPa. On the one hand, the low-manganese and low-carbon pre-alloyed powder, as a skeleton powder, requires a higher pressure to overcome the mechanical interlocking resistance between large particles. On the other hand, the large particle matrix of the low-manganese and low-carbon pre-alloyed powder is effectively matched with high-manganese and high-carbon pre-alloyed powder, copper powder, and graphite powder of different particle sizes. Appropriate pressing pressure avoids fine powder agglomeration, which leads to uneven pressing, accelerates particle rearrangement, improves the density of the green body, and enhances the strength of the green body. However, excessive pressure (above 850 MPa) will increase mold wear.

[0050] In one embodiment, the green body is pressed into shape at 650–750 MPa.

[0051] In liquid-phase sintering, temperature gradient control has a significant impact on the uniformity of the microstructure. Because the raw material powder of this invention uses a variety of particle size combinations, and the particle sizes of the matrix powder and activator differ considerably, deformation is easily caused by rapid heating and pressing. Controlling the gradient sintering process can also prevent material deformation due to rapid heating during sintering. Temperature gradient control directly affects the microstructure and properties of the material, and gradient sintering can also prevent material deformation due to rapid heating during sintering. In this invention, the sintering process involves first heating to 350–450 °C and holding for 30–40 min, then raising the temperature to 700–800 °C and holding for 30–40 min, and finally raising the temperature to 1150–1270 °C and holding for 1.5–2.5 h. Holding at 350–450 °C and 700–800 °C avoids large temperature gradients that could increase internal thermal stress, affecting material density and uniformity. Furthermore, these two stages of heating and holding provide a temperature basis for subsequent liquid phase formation, accelerating liquid phase formation and diffusion during sintering at 1150–1270 °C. This results in a more uniform liquid phase distribution, preventing component segregation caused by sudden high temperatures, improving microstructure uniformity, and ultimately enhancing material density and mechanical properties. Hardness exceeds 78 HRC, a 50% improvement over conventional products, and density reaches 7.6 g / cm³. 3 above.

[0052] In one embodiment, the sintering temperature is raised to 380–430 °C and held for 30–40 min, then raised to 730–780 °C and held for 30–40 min, and then raised to 1170–1240 °C and held for 1.5–2.5 h to obtain the composite activated high-hardness non-magnetic steel.

[0053] Example 1:

[0054] A method for preparing composite activated high-hardness non-magnetic steel, the raw material powder used includes: low manganese and low carbon pre-alloy powder as the matrix, and 8% by weight of high manganese and high carbon pre-alloy powder, 4% by weight of graphite powder and 2% by weight of copper powder as composite activators.

[0055] The low-manganese, low-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 11%, C 0.7%, Si 0.5%, V 1.5%, rare earth Y 0.15%, S 0.03%, P 0.03%, O 0.05%, with the balance being Fe;

[0056] The high-manganese, high-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 40%, C 2.5%, Si 0.9%, S 0.03%, P 0.04%, O 0.05%, with the balance being Fe.

[0057] The low-manganese, low-carbon pre-alloyed powder has a particle size of 110 μm.

[0058] The high-manganese, high-carbon pre-alloyed powder has a particle size of 40 μm.

[0059] The graphite powder has a particle size of 18 μm; the copper powder has a particle size of 30 μm.

[0060] Alloy powder green preparation: The raw material powder is thoroughly mixed in a V-type mixer and pressed into an alloy powder green under 600MPa;

[0061] Sintering: The alloy powder green billet is sintered in a mesh belt sintering furnace with a sintering atmosphere of 80% nitrogen and 20% hydrogen. The temperature is raised to 350 °C and held for 40 min, then raised to 700 °C and held for 40 min, and then raised to 1150 °C and held for 2.5 h to obtain the composite activated high hardness non-magnetic steel.

[0062] Example 2:

[0063] A method for preparing composite activated high-hardness non-magnetic steel, the raw material powder used includes: low manganese and low carbon pre-alloy powder as the matrix, and 15% by weight of high manganese and high carbon pre-alloy powder, 3% by weight of graphite powder and 1.5% by weight of copper powder as composite activators.

[0064] The low-manganese, low-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 9%, C 0.6%, Si 0.4%, V 1.0%, rare earth Y 0.10%, S 0.03%, P 0.03%, O 0.05%, with the balance being Fe;

[0065] The high-manganese, high-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 35%, C 2.0%, Si 0.7%, S 0.03%, P 0.04%, O 0.05%, with the balance being Fe.

[0066] The low-manganese, low-carbon pre-alloyed powder has a particle size of 120 μm.

[0067] The high-manganese, high-carbon pre-alloyed powder has a particle size of 50 μm.

[0068] The graphite powder has a particle size of 15 μm; the copper powder has a particle size of 35 μm.

[0069] Alloy powder green preparation: The raw material powder is thoroughly mixed in a V-type mixer and pressed into shape at 650MPa to obtain alloy powder green.

[0070] Sintering: The alloy powder green billet is sintered in a mesh belt sintering furnace with a sintering atmosphere of 80% nitrogen and 20% hydrogen. The temperature is raised to 380 °C and held for 40 min, then raised to 730 °C and held for 40 min, and then raised to 1170 °C and held for 2.0 h to obtain the composite activated high hardness non-magnetic steel.

[0071] Example 3:

[0072] A method for preparing composite activated high-hardness non-magnetic steel, using raw material powder comprising: low-manganese low-carbon pre-alloyed powder as the matrix, and 20% by weight of high-manganese high-carbon pre-alloyed powder, 2% by weight of graphite powder, and 1% by weight of copper powder as composite activators.

[0073] The low-manganese, low-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 8%, C 0.4%, Si 0.7%, V 0.5%, rare earth Y 0.05%, S 0.03%, P 0.03%, O 0.05%, with the balance being Fe;

[0074] The high-manganese, high-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 25%, C 1.5%, Si 0.6%, S 0.03%, P 0.01%, O 0.05%, with the balance being Fe.

[0075] The low-manganese, low-carbon pre-alloyed powder has a particle size of 180 μm.

[0076] The high-manganese, high-carbon pre-alloyed powder has a particle size of 80 μm.

[0077] The graphite powder has a particle size of 13 μm; the copper powder has a particle size of 40 μm.

[0078] Preparation of alloy powder green body: The raw material powder is thoroughly mixed in a V-type mixer and pressed into shape at 750MPa to obtain alloy powder green body;

[0079] Sintering: The alloy powder green billet is sintered in a mesh belt sintering furnace with a sintering atmosphere of 80% nitrogen and 20% hydrogen. The temperature is raised to 430 °C and held for 35 min, then raised to 780 °C and held for 35 min, and then raised to 1240 °C and held for 1.5 h to obtain the composite activated high hardness non-magnetic steel.

[0080] Example 4:

[0081] A method for preparing composite activated high-hardness non-magnetic steel, using raw material powder comprising: low-manganese low-carbon pre-alloyed powder as the matrix, and 16% by weight of high-manganese high-carbon pre-alloyed powder, 2.6% by weight of graphite powder, and 1.3% by weight of copper powder as composite activators.

[0082] The low-manganese, low-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 10%, C 0.5%, Si 0.6%, V 0.8%, rare earth Y 0.08%, S 0.04%, P 0.03%, O 0.03%, with the balance being Fe;

[0083] The high-manganese, high-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 30%, C 1.9%, Si 0.5%, S 0.03%, P 0.04%, O 0.02%, with the balance being Fe.

[0084] The low-manganese, low-carbon pre-alloyed powder has a particle size of 150 μm.

[0085] The high-manganese, high-carbon pre-alloyed powder has a particle size of 70 μm.

[0086] The graphite powder has a particle size of 5 μm; the copper powder has a particle size of 37 μm.

[0087] Alloy powder green preparation: The raw material powder is thoroughly mixed in a V-type mixer and pressed into shape at 850MPa to obtain alloy powder green.

[0088] Sintering: The alloy powder green billet is sintered in a mesh belt sintering furnace with a sintering atmosphere of 80% nitrogen and 20% hydrogen. The temperature is raised to 450 °C and held for 30 min, then raised to 800 °C and held for 30 min, and then raised to 1270 °C and held for 1.5 h to obtain the composite activated high hardness non-magnetic steel.

[0089] Comparative Example 1

[0090] The preparation method of the composite activated high-hardness non-magnetic steel in Comparative Example 1 differs from that in Example 2 only in that the raw material powder used includes: low manganese and low carbon pre-alloy powder as the matrix, and 4% by weight of high manganese and high carbon pre-alloy powder, 4% by weight of graphite powder, and 1.5% by weight of copper powder as composite activators.

[0091] Comparative Example 2

[0092] The preparation method of the composite activated high-hardness non-magnetic steel in Comparative Example 2 differs from that in Example 2 only in that the raw material powder used includes: low manganese and low carbon pre-alloy powder as the matrix, and 22% by weight of high manganese and high carbon pre-alloy powder, 1.5% by weight of graphite powder, and 1.0% by weight of copper powder as composite activators.

[0093] Comparative Example 3

[0094] The preparation method of the composite activated high-hardness non-magnetic steel in Comparative Example 3 differs from that in Example 2 only in that the low-manganese and low-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 7%, C 0.3%, Si 0.6%, V 0.8%, rare earth Y 0.08%, S 0.04%, P 0.03%, O 0.03%, with the balance being Fe;

[0095] The high-manganese, high-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 23%, C 1.9%, Si 0.5%, S 0.03%, P 0.04%, O 0.02%, with the balance being Fe.

[0096] Comparative Example 4

[0097] The only difference between the preparation method of the composite activated high-hardness non-magnetic steel in Comparative Example 4 and Example 2 is that the low-manganese and low-carbon pre-alloy powder has a particle size of 90 μm; the high-manganese and high-carbon pre-alloy powder has a particle size of 40 μm; the graphite powder has a particle size of 20 μm; and the copper powder has a particle size of 40 μm.

[0098] Comparative Example 5

[0099] The only difference between the preparation method of the composite activated high hardness non-magnetic steel in Comparative Example 5 and Example 2 is that: alloy powder green preparation: the raw material powder is fully mixed evenly in a V-type mixer and pressed into an alloy powder green at 480 MPa.

[0100] Comparative Example 6

[0101] The preparation method of the composite activated high-hardness non-magnetic steel in Comparative Example 6 differs from that in Example 2 only in that:

[0102] Sintering: The alloy powder green billet is sintered in a mesh belt sintering furnace with a sintering atmosphere of 80% nitrogen and 20% hydrogen. It is directly heated to 1170 °C and held for 2.0 h to obtain the composite activated high hardness non-magnetic steel.

[0103] The composite activated high-hardness non-magnetic steel materials prepared in Examples 1-4 and Comparative Examples 1-6 were subjected to performance tests, and the results are shown in Table 1.

[0104] Table 1: Performance data of non-magnetic steel materials prepared in the examples and comparative examples

[0105] <![CDATA[Sintered density (g / cm 3 ).]]> Tensile strength (MPa) Hardness (HRC) Example 1 7.7 565 79 Example 2 8.0 570 83 Example 3 7.6 578 78 Example 4 7.9 594 81 Comparative Example 1 5.9 430 63 Comparative Example 2 6.1 455 60 Comparative Example 3 6.5 411 59 Comparative Example 4 6.0 415 65 Comparative Example 5 5.4 375 57 Comparative Example 6 5.7 352 72

[0106] As can be seen from Table 1, the sintering density of the composite activated high-hardness non-magnetic steel prepared by this invention is 7.6 g / cm³. 3 The tensile strength is above 565 MPa, the hardness is above 78 HRC, and the non-magnetic steel material obtained by sintering has high density, high hardness and high strength, with the hardness being more than 50% higher than that of conventional products.

[0107] Adjusting the mass ratio of high-manganese, high-carbon pre-alloyed powder to graphite powder and copper powder in Comparative Examples 1-2 failed to guarantee a good sintering composite activation effect. The sintering density of the non-magnetic steel decreased sharply, the tensile strength decreased, and the hardness decreased significantly.

[0108] After adjusting the composition of the low-manganese and low-carbon pre-alloyed powder in Comparative Example 3 and the particle size of the matrix and activator powder in Comparative Example 4, the large particle matrix of the low-manganese and low-carbon pre-alloyed powder could not be effectively matched with high-manganese and high-carbon pre-alloyed powder, copper powder, and graphite powder of different particle sizes. Consequently, the gaps between particles could not be fully filled, the compact density could not be increased, the composite activation effect during the sintering process could not be improved, the liquid phase could not be obtained quickly, and the density and hardness of the non-magnetic steel could not be increased. This resulted in a sharp decrease in sintering density, a decrease in tensile strength, and a significant decrease in hardness.

[0109] Comparative Examples 5-6 show that adjusting the green compact pressing pressure too low can lead to uneven pressing, reduced green compact density and strength, and adjusting the sintering to use a single sintering process can cause temperature rise and material deformation, directly affecting the material's microstructure and properties, resulting in a sharp decrease in sintering density, reduced tensile strength, and a significant decrease in hardness.

[0110] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A composite activated high-hardness non-magnetic steel, characterized in that, The raw material powder used includes: low-manganese and low-carbon pre-alloyed powder as the matrix, combined with 8-20% by weight of high-manganese and high-carbon pre-alloyed powder, 2-4% by weight of graphite powder, and 1-2% by weight of copper powder as a composite activator. The mass ratio of high-manganese and high-carbon pre-alloyed powder to graphite powder and copper powder is 4-10:2:

1. The raw material powder is used to obtain the composite activated high-hardness non-magnetic steel by powder metallurgy. The low-manganese, low-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 8-11%, C 0.4-0.7%, Si 0.5-0.7%, V 0.5-1.5%, rare earth Y 0.05-0.15%, S≤0.05%, P≤0.1%, O≤0.15%, with the balance being Fe; The high-manganese, high-carbon pre-alloyed powder comprises the following components by weight percentage: Mn 25-40%, C 1.5-2.5%, Si 0.5-0.9%, S≤0.05%, P≤0.1%, O≤0.15%, with the balance being Fe.

2. The composite activated high-hardness non-magnetic steel according to claim 1, characterized in that, The low-manganese, low-carbon pre-alloyed powder has a particle size of 110–180 μm. The high-manganese, high-carbon pre-alloyed powder has a particle size of 40–80 μm. The graphite powder has a particle size of less than 20 μm; the copper powder has a particle size of 30–40 μm.

3. The composite activated high-hardness non-magnetic steel according to claim 2, characterized in that, The low-manganese, low-carbon pre-alloyed powder has a particle size of 120–150 μm. The high-manganese, high-carbon pre-alloyed powder has a particle size of 50–70 μm. The particle size of graphite powder is 5–15 μm; the particle size of copper powder is 30–35 μm.

4. A method for preparing a composite activated high-hardness non-magnetic steel according to any one of claims 1-3, characterized in that, Alloy powder green preparation: The raw material powder is thoroughly mixed in a mixer and pressed into a green shape at 550-850 MPa to obtain the alloy powder green. Sintering: The alloy powder green billet is sintered in a mesh belt sintering furnace under a nitrogen and hydrogen mixture atmosphere. The temperature is raised to 350-450 °C and held for 30-40 min, then raised to 700-800 °C and held for 30-40 min, and then raised to 1150-1270 °C and held for 1.5-2.5 h to obtain the composite activated high-hardness non-magnetic steel.

5. The method for preparing composite activated high-hardness non-magnetic steel according to claim 4, characterized in that, The green body is pressed and formed at 650-750 MPa.

6. The method for preparing composite activated high-hardness non-magnetic steel according to claim 4, characterized in that, The sintering process involves heating the material to 380–430 °C and holding it for 30–40 min, then raising the temperature to 730–780 °C and holding it for 30–40 min, followed by raising the temperature to 1170–1240 °C and holding it for 1.5–2.5 h to obtain the composite activated high-hardness non-magnetic steel.

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