A fine-grained high-strength soft magnetic stainless steel reinforced by ta and cu, a profile containing the same, and a method for producing the profile

Abstract

The present application belongs to the field of stainless steel. Specifically, the present application relates to a fine-grained high-strength and high-toughness soft magnetic stainless steel synergistically strengthened by Ta and Cu and a soft magnetic stainless steel profile comprising the same. The soft magnetic stainless steel of the present application is composed of elements Cr, Cu, Mo, Ta, C, Fe and inevitable impurities. In the preparation process of the soft magnetic stainless steel profile of the present application, the composition is dosed and smelted, and then subjected to solid solution, hot rolling, cold drawing, recrystallization annealing and aging, etc. The process parameters in each process are strictly controlled, so that a soft magnetic stainless steel profile with fine and uniform structure, trace carbide precipitation and high-density dispersed coherent nanometer precipitate co-strengthening, and excellent low-temperature toughness and soft magnetic properties is prepared. The fine-grained high-strength and high-toughness soft magnetic stainless steel profile synergistically strengthened by Ta and Cu of the present application can be effectively applied to electromagnetic valves and related products that serve in low-temperature medium and require certain strength and toughness, and has good popularization prospect and application value.

Description

Technical Field

[0001] This invention relates to the field of stainless steel technology. Specifically, this invention relates to a soft magnetic stainless steel and a soft magnetic stainless steel profile comprising the same, and further relates to a method for preparing the soft magnetic stainless steel profile and articles prepared from the soft magnetic stainless steel profile. Background Technology

[0002] With the continuous development of miniaturization, high frequency, and high power in high-end electromagnetic actuation components, their core soft magnetic components are also facing increasingly higher performance requirements. Electromagnetic devices, such as precision fuel injection valves and micro servo motors, require their ferritic soft magnetic stainless steel cores to maintain high saturation magnetic induction and low magnetic loss, while also possessing higher mechanical strength and toughness reserves to withstand long-term, high-frequency complex stress impacts.

[0003] Currently, conventional ferritic soft magnetic stainless steels primarily enhance strength through solid solution strengthening or the introduction of numerous dislocations. However, these methods have inherent limitations: while excessive and complex solid solution atoms and intense plastic deformation effectively increase strength, they also strongly pin magnetic domain walls, leading to a sharp increase in coercivity and sacrificing the material's ductility and toughness. Fine-grain strengthening and nanoprecipitation strengthening are necessary technical pathways to overcome these performance limitations.

[0004] However, existing technologies still face challenges in the synergistic control of multi-scale microstructures. Achieving stable, fine-grained, and uniform grain structure in soft magnetic stainless steel while simultaneously introducing dispersed nanoprecipitates with controllable size distribution is a complex systems engineering project involving the entire process of alloy design, hot working, and heat treatment. Currently, the field of soft magnetic stainless steel technology urgently needs an industrialized technical solution that systematically coordinates grain refinement strengthening and nanoprecipitation strengthening to achieve synergistic breakthroughs in multiple performance indicators, including strength, low-temperature toughness, and soft magnetic properties. Summary of the Invention

[0005] Purpose of the invention

[0006] In view of the problems existing in the prior art described in the background section above, the object of the present invention is to provide a fine-grained, high-strength, and high-toughness soft magnetic stainless steel synergistically strengthened by Ta and Cu, and a soft magnetic stainless steel profile comprising the soft magnetic stainless steel. A further object of the present invention is to provide a method for preparing the soft magnetic stainless steel profile, and an article prepared from the soft magnetic stainless steel profile.

[0007] Technical solution

[0008] In order to achieve the objectives of the present invention as described above, the present invention provides the following technical solutions:

[0009] Option 1: A fine-grained, high-strength, and high-toughness soft magnetic stainless steel synergistically strengthened by Ta and Cu, wherein the soft magnetic stainless steel is composed of elements Cr (chromium), Cu (copper), Mo (molybdenum), Ta (tantalum), C (carbon), Fe (iron) and unavoidable impurities, and the content of the elements is as follows:

[0010] Based on the total weight of the soft magnetic stainless steel:

[0011] The element Cr content by weight percentage [Cr] is from about 14.0% to about 18.0% by weight.

[0012] The elemental Cu has a weight percentage content of approximately 1.5% to approximately 3.0% by weight.

[0013] The element Mo has a weight percentage content of about 1.0 to about 2.0% by weight.

[0014] The weight percentage content of element Ta [Ta] is from about 0.2% to about 0.5% by weight;

[0015] The weight percentage content of element C [C] is from about 0.01 to about 0.03% by weight;

[0016] The balance is Fe and unavoidable impurities.

[0017] Option 2: The soft magnetic stainless steel according to Option 1 above, wherein, based on the total weight of the soft magnetic stainless steel, the element considered as the unavoidable impurity is:

[0018] The weight percentage content of N (nitrogen) [N] is controlled to be below about 0.005% by weight; and / or

[0019] The weight percentage content of O (oxygen) [O] is controlled to be below about 0.005% by weight; and / or

[0020] The weight percentage content of sulfur [S] is controlled to be below approximately 0.005% by weight; and / or

[0021] The weight percentage content of phosphorus [P] is controlled to be below about 0.005% by weight.

[0022] Option 3: The soft magnetic stainless steel according to Option 1 or 2 above, wherein the weight percentage content of element Ta [Ta] and the weight percentage content of element C [C] in the soft magnetic stainless steel meet the following requirements:

[0023] [Ta] + [C] = approximately 0.2-0.5% by weight, and / or

[0024] [Ta] : [C] = Approximately (16-30):1.

[0025] Option 4: A Ta-Cu synergistically strengthened fine-grained high-strength and high-toughness soft magnetic stainless steel profile comprising Ta and Cu synergistically strengthened fine-grained high-strength and high-toughness soft magnetic stainless steel according to any one of Options 1 to 3 above.

[0026] Option 5: The soft magnetic stainless steel profile according to Option 4 above, wherein the soft magnetic stainless steel profile has one or more of the following properties:

[0027] The yield strength R of the soft magnetic stainless steel profile e Approximately ≥ 650 MPa;

[0028] The tensile strength R of the soft magnetic stainless steel profile m Approximately ≥ 750 MPa;

[0029] The elongation e of the soft magnetic stainless steel profile is approximately ≥ 25%;

[0030] The impact energy (KV2) of the soft magnetic stainless steel profile at -40℃ is approximately ≥ 30 J;

[0031] The saturation magnetic induction intensity B of the soft magnetic stainless steel profile s Approximately ≥ 1.50 T;

[0032] The coercivity H of the soft magnetic stainless steel profile c It is approximately ≤ 300 A / m;

[0033] The microstructure of the soft magnetic stainless steel profile contains approximately 99.99% or more ferrite, and

[0034] The effective grain size of the microstructure of the soft magnetic stainless steel profile is approximately ≤ 15 μm.

[0035] Option 6: A method for preparing a fine-grained, high-strength, and tough soft magnetic stainless steel profile with Ta and Cu synergistic reinforcement according to Option 4 or 5 above, wherein the method includes the following steps:

[0036] Step 1: Provide molten steel and cast it into a billet. The molten steel consists of the elements Cr, Cu, Mo, Ta, C, Fe, and unavoidable impurities. The content of these elements is as follows:

[0037] Based on the total weight of the molten steel

[0038] The element Cr content by weight percentage [Cr] is from about 14.0% to about 18.0% by weight.

[0039] The elemental Cu has a weight percentage content of approximately 1.5% to approximately 3.0% by weight.

[0040] The element Mo has a weight percentage content of about 1.0 to about 2.0% by weight.

[0041] The weight percentage content of element Ta [Ta] is from about 0.2% to about 0.5% by weight;

[0042] The weight percentage content of element C [C] is from about 0.01 to about 0.03% by weight;

[0043] And the balance is Fe and unavoidable impurities;

[0044] Step 2: The billet obtained from Step 1 is subjected to solution heat treatment, preferably for about 6 to about 10 hours, wherein preferably, the temperature of the solution heat treatment is... ,in, This indicates that the value of T1 in °C is rounded up, where

[0045] T1= 1080+ 3550 × [C]+ 375 × [Ta];

[0046] in,

[0047] [Ta] represents the weight percentage content of element Ta in the molten steel, expressed as a percentage by weight.

[0048] [C] represents the weight percentage content of element C in the molten steel, expressed as a percentage by weight.

[0049] Step 3: Roll the solution-treated billet obtained from Step 2 into a billet, wherein preferably, the total deformation rate caused by the rolling is in the range of about 98% to about 99.5%, the initial rolling temperature is in the range of about 1120°C to about 1180°C, the billet is not reheated during the rolling process, and the final rolling temperature is not less than about 850°C, then the billet is air-cooled to about 780°C to about 820°C, and finally cooled to a temperature of about 40°C or less at a cooling rate of not less than about 30°C / s;

[0050] Step 4: The rolled and cooled billet obtained from Step 3 is subjected to multiple cold drawing to obtain a profile, wherein preferably, the total elongation μ resulting from the cold drawing is in the range of about 1.4 to about 1.7, the elongation resulting from a single cold drawing is not more than about 1.2, and no heat treatment is performed during the cold drawing process.

[0051] Step 5: The profile obtained from step 4 after cold drawing is subjected to recrystallization annealing at a temperature preferably from about 930°C to about 970°C, and then cooled to a temperature below about 40°C at a cooling rate of not less than about 30°C / s. Preferably, the holding time for recrystallization annealing is:

[0052] (1) When the cross-sectional area S of the profile is ≤ approximately 100 mm2 At that time, the holding time for the recrystallization annealing was approximately 5 minutes, and

[0053] (2) When the cross-sectional area S of the profile is greater than approximately 100 mm 2 At that time, the holding time for the recrystallization annealing is ,in, The value of t1 in minutes is rounded up, where

[0054] t1 = 5 + [0.085 × (S - 100)] / μ,

[0055] Where S is in mm 2 The cross-sectional area of ​​the profile is expressed in units of μ, where μ is the total elongation coefficient caused by the cold drawing.

[0056] Step 6: The recrystallized profile obtained from Step 5 is subjected to aging treatment at a temperature preferably from about 600°C to about 700°C, and then cooled to a temperature below about 40°C at a cooling rate of not less than about 30°C / s, thereby forming the soft magnetic stainless steel profile. Preferably, the holding time of the aging treatment is:

[0057] (1) When the cross-sectional area S of the profile is ≤ approximately 100 mm 2 At that time, the heat preservation time of the aging treatment is ,in The value of t2 in minutes is rounded up, where

[0058] t2 = 75 - T / 10,

[0059] Where T is the holding temperature of the aging treatment, in °C; and

[0060] (2) When the cross-sectional area S of the profile is greater than approximately 100 mm 2 At that time, the heat preservation time of the aging treatment is ,in The value of t3 in minutes is rounded up, where

[0061] t3 = 70 - T / 10 + S / 20

[0062] Where T is the holding temperature of the aging treatment in °C; and S is in mm. 2 The cross-sectional area of ​​the profile is expressed in units of .

[0063] Option 7: An article made from a soft magnetic stainless steel profile according to Option 4 or 5 above, or from a soft magnetic stainless steel profile prepared according to the preparation method described in Option 6 above.

[0064] Technical effect

[0065] The fine-grained, high-strength, and tough soft magnetic stainless steel of this invention, synergistically strengthened by Ta and Cu, employs a rational chemical composition design. It optimizes and eliminates many alloying elements commonly used in other soft magnetic stainless steels, such as Mn (manganese), Ni (nickel), Al (aluminum), Si (silicon), and V (vanadium), while retaining Cr (chromium). It also strictly controls the content of impurity elements such as N (nitrogen), O (oxygen), S (sulfur), and P (phosphorus) to fully ensure that the profiles containing the soft magnetic stainless steel possess excellent soft magnetic properties. Simultaneously, the soft magnetic stainless steel of this invention strictly controls the Ta (… The content and ratio of tantalum (Ta) and carbon (C) are controlled by using Ta to fix the C element. The heat treatment process is precisely controlled by a formula to ensure that tantalum carbide (TaC) precipitation is dispersed in the ferrite matrix. Combined with appropriate cold deformation and precise recrystallization, the dispersed TaC significantly increases the recrystallization nucleation rate and pins grain boundaries, resulting in a fine recrystallized structure. Simultaneously, the dispersed TaC precipitation also hinders dislocation movement during deformation, giving the soft magnetic stainless steel profile containing this invention both excellent yield strength and low-temperature toughness. Furthermore, a certain amount of Cu (copper) and Mo (molybdenum) are introduced into the soft magnetic stainless steel of this invention. The precipitation evolution of Cu is precisely controlled through an appropriate aging process, resulting in the dispersed precipitation of Cu as a B2-Cu nanophase completely coherent with the ferrite matrix. This improves the tensile strength of the profile while avoiding deterioration of low-temperature toughness. The solid solution strengthening effect of Mo further enhances the tensile strength and improves corrosion resistance.

[0066] Furthermore, the preparation method of the soft magnetic stainless steel profile of the present invention adopts a real-time controlled heat treatment process. Through experimental calculations, a solution treatment process that dynamically changes with the content of Ta and C elements was formulated, so that TaC can be completely dissolved to achieve the subsequent dispersion precipitation of TaC. Through kinetic calculations, a recrystallization process that dynamically changes with the cross-sectional area and total elongation coefficient of the profile after cold drawing was formulated, ensuring that recrystallization can occur fully and that the grains will not grow excessively. Through precipitation kinetic calculations, an aging process that dynamically changes with the aging temperature and the cross-sectional area of ​​the profile was formulated, ensuring that the Cu-rich phase can be dispersedly precipitated in the ferrite matrix and that the precipitation form is mainly B2-Cu phase.

[0067] The soft magnetic stainless steel profile of this invention possesses excellent mechanical properties and low-temperature toughness, as well as excellent soft magnetic properties, such as high saturation magnetic induction and low coercivity. Specifically, this is reflected in: yield strength R e ≥ Approximately 650 MPa, tensile strength R m ≥ Approximately 750 MPa, elongation e ≥ Approximately 25%, impact energy at -40℃ KV2 ≥ Approximately 30 J, saturation magnetic induction intensity B s ≥ Approximately 1.50 T, coercivity Hc ≤ Approximately 300 A / m, and grain size ≤ Approximately 15 μm.

[0068] The soft magnetic stainless steel profile of this invention has fine grains and dispersed precipitates. Furthermore, the B2-Cu nanoprecipitates are completely coherent with the matrix, exhibiting excellent "strength-plasticity-toughness-magnetism" coupling properties. It can be effectively applied to electromagnetic valve cores and related products that operate in complex stress and low-temperature media, and has very good prospects for promotion and application value.

[0069] In addition, the alloying elements contained in the soft magnetic stainless steel of the present invention remove Al, Si and Nb (niobium) elements from traditional soft magnetic stainless steel, and contain no more than about 18% by weight of Cr, no more than 3.0% by weight of Cu and no more than 2.0% by weight of Mo and trace amounts of Ta, making the profile preparation process of the present invention simple and conventional, with suitable alloy cost and preparation cost. Attached Figure Description

[0070] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0071] Figure 1 This is a metallographic photograph of the soft magnetic stainless steel profile of Embodiment 1 of the present invention.

[0072] Figure 2 This is a metallographic photograph of the soft magnetic stainless steel profile of Embodiment 2 of the present invention.

[0073] Figure 3 This is a metallographic photograph of the soft magnetic stainless steel profile of Embodiment 3 of the present invention.

[0074] Figure 4 This is a metallographic photograph of the soft magnetic stainless steel profile of Embodiment 4 of the present invention. Detailed Implementation

[0075] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely for the purpose of aiding understanding of this invention and should not be considered as specific limitations on this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Process parameters in the following embodiments that are not specifically specified are generally performed under conventional conditions.

[0076] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. The term "about" as used in this invention means that the number it modifies may fluctuate within ±20%, ±15%, ±10%, ±5%, or ±2% of that number. For numerical ranges, the endpoint values ​​of various ranges, the endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0077] In a first aspect, the present invention provides a fine-grained, high-strength, and high-toughness soft magnetic stainless steel synergistically strengthened by Ta and Cu. The soft magnetic stainless steel according to the first aspect of the present invention is composed of the elements Cr, Cu, Mo, Ta, C, Fe, and unavoidable impurities, the contents of which are:

[0078] Based on the total weight of the soft magnetic stainless steel:

[0079] The element Cr content by weight percentage [Cr] is approximately 14.0 to 18.0% by weight.

[0080] The elemental Cu content is approximately 1.5% to 3.0% by weight.

[0081] The element Mo has a weight percentage content of approximately 1.0 to 2.0% [Mo] %.

[0082] The element Ta has a weight percentage content of approximately 0.2 to 0.5% by weight.

[0083] The weight percentage content of element C [C] is about 0.01 to 0.03% by weight;

[0084] The balance is Fe and unavoidable impurities.

[0085] In the soft magnetic stainless steel of the first aspect of the present invention, Cr is an element that promotes the formation of ferrite structure and is also a major element that makes stainless steel less prone to rusting. In the soft magnetic stainless steel of the present invention, Cr is one of the basic elements. As the Cr content in the stainless steel increases, the pitting potential of the ferritic stainless steel increases, and its corrosion resistance also improves. However, as the Cr content increases, the saturation magnetization of the material decreases. Therefore, in the soft magnetic stainless steel of the present invention, the Cr content is controlled within the range of about 14% to about 18% by weight, for example, it can be set to about 15% by weight, about 16% by weight, or about 17% by weight.

[0086] In the soft magnetic stainless steel of the first aspect of the present invention, Cu is the main precipitation strengthening element. Cu has very low solid solubility in steel; at room temperature, the solid solubility of Cu in ferritic stainless steel is almost zero. By aging the Cu-containing supersaturated solid solution, Cu can be dispersed and precipitated in large quantities from the ferrite matrix. When Cu precipitates in the ferrite matrix, it undergoes a series of structural evolutions: solid solution state – B2 – BCC – 9R – FCC. By precisely controlling the aging temperature and aging time, the nano-Cu-rich phase is mainly precipitated as the B2-Cu phase coherent with the matrix, thus achieving high strength and toughness without sacrificing the matrix's ductility and toughness. However, Cu is a weak austenite-forming element, and excessive Cu will significantly reduce the material's magnetic permeability. More importantly, when the Cu content exceeds a critical value, it may induce surface hot brittleness during thermal processing, severely affecting the stability of the rolling process. Therefore, in the soft magnetic stainless steel of the present invention, the content of element Cu needs to be precisely controlled in the range of about 1.5 to about 3.0% by weight, specifically, for example, about 1.7% by weight, about 2.0% by weight, about 2.2% by weight, about 2.5% by weight or about 2.8% by weight.

[0087] In the soft magnetic stainless steel of the first aspect of the present invention, Mo is a strong ferrite-forming element and also has a significant solid solution strengthening effect. Mo can effectively improve the stainless steel's resistance to pitting and crevice corrosion. However, excessive Mo will promote the precipitation of intermetallic phases (such as the σ phase). These hard and brittle phases not only reduce the impact toughness of the material but also disrupt the matrix continuity, leading to deterioration of magnetic properties. Therefore, in the soft magnetic stainless steel of the present invention, the content of element Mo needs to be precisely controlled within the range of about 1.0 to about 2.0% by weight, specifically, for example, about 1.2% by weight, about 1.5% by weight, or about 1.8% by weight.

[0088] In the soft magnetic stainless steel of the first aspect of the present invention, Ta is a microalloying element and a strong carbide and nitride forming element. Ta can form carbides and nitrides with C and N elements in stainless steel, inhibiting the precipitation of carbides and nitrides formed by Cr in stainless steel, thereby enhancing the intergranular corrosion resistance of stainless steel. Ta precipitates can also pin grain boundaries and dislocations, inhibit grain growth, and play a role in refining grains, increasing yield strength, and improving impact toughness. Therefore, in the soft magnetic stainless steel of the present invention, the content of element Ta should be controlled in the range of about 0.2% to about 0.5% by weight, for example, it can be set to about 0.25% by weight, about 0.30% by weight, about 0.35% by weight, about 0.40% by weight, or about 0.45% by weight.

[0089] In the soft magnetic stainless steel of the first aspect of the present invention, carbon (C) is an interstitial solid solution element that can form TaC precipitates with Ta. Through appropriate heat treatment, finely dispersed TaC can be formed in the ferrite matrix, thereby pinning grain boundaries and dislocations, inhibiting grain growth, refining the grains, increasing yield strength, and improving impact toughness. However, carbon is a strong austenite-forming element; excessively high carbon content will reduce ferrite stability and affect soft magnetic properties. Furthermore, unfixed carbon elements will combine with chromium (Cr) to form continuously distributed chromium (M) at the grain boundaries. 23 C6-type precipitates significantly deteriorate the ductility, toughness, and corrosion resistance of stainless steel. Therefore, in the soft magnetic stainless steel of the present invention, the content of element C should be controlled within the range of about 0.01 to about 0.03% by weight, for example, it can be set to about 0.012% by weight, about 0.015% by weight, about 0.020% by weight, about 0.025% by weight, or about 0.028% by weight.

[0090] In some preferred embodiments of the soft magnetic stainless steel of the first aspect of the present invention, the weight percentage content of element Ta [Ta] and the weight percentage content of element C [C] in the soft magnetic stainless steel further need to meet the following requirements:

[0091] [Ta] + [C] = about 0.2% to about 0.5% by weight, for example, about 0.25% by weight, about 0.3% by weight, or about 0.4% by weight.

[0092] [Ta] : [C] = (16-30):1, for example, 18:1, 24:1 or 28:1.

[0093] Here, the sum of the weight percentage content of element Ta [Ta] and element C [C] should not be too large, for example, it should not exceed about 0.5% by weight, otherwise it may cause TaC precipitation to be distributed in clusters and tend to coarsen, weakening the effect of pinning grain boundaries and dislocations and greatly deteriorating the ductility and toughness; nor should it be too small, for example, it should not be less than about 0.2% by weight, otherwise it may cause insufficient distribution of TaC precipitation, which will not be able to effectively pin grain boundaries and dislocations and will not achieve the expected strength improvement effect.

[0094] In addition, the weight ratio of the element Ta [Ta] to the element C [C] should not be too large, for example, not exceeding about 30:1, otherwise some Ta and Mo elements may combine to form the Chi phase, which will worsen the impact toughness; nor should it be too small, for example, not lower than about 16:1, otherwise the C element may not be completely fixed, and the remaining C atoms, whether dissolved in the matrix or combined with Cr to form the M23C6 phase, will worsen the impact performance and soft magnetic properties.

[0095] In some other preferred embodiments of the soft magnetic stainless steel of the first aspect of the present invention, it is preferable to strictly control the content of elements N, O, S and P, which are unavoidable impurities.

[0096] Element nitrogen (N), as an unavoidable impurity, is preferably completely absent from the soft magnetic stainless steel of the present invention. Nitrogen is a strong austenite-forming element, which has a detrimental effect on the magnetic properties of ferritic stainless steel. Furthermore, nitrogen has low solubility and readily precipitates as nitrides with other alloying elements, causing localized distortion within the stainless steel, creating a stress field, hindering domain wall movement, increasing magnetic loss, and weakening magnetic induction and permeability. Therefore, in the soft magnetic stainless steel of the first aspect of the present invention, the content of element nitrogen is typically controlled to be below about 0.005% by weight, preferably below about 0.003% by weight.

[0097] Element O, as an unavoidable impurity, is preferably completely absent from the soft magnetic stainless steel of the present invention. Element O is generally considered a harmful residual element in the soft magnetic stainless steel of the present invention. It may precipitate from the molten steel as oxide inclusions along with other alloying elements during the smelting process, significantly weakening almost all properties of the soft magnetic stainless steel of the present invention, including mechanical properties, corrosion resistance, low-temperature toughness, and soft magnetic properties. Therefore, in the soft magnetic stainless steel of the first aspect of the present invention, the content of element O is typically controlled to be below about 0.005% by weight, preferably below about 0.003% by weight, more preferably below about 0.002% by weight, further preferably below about 0.0015% by weight, and most preferably below about 0.001% by weight.

[0098] Element S, as an unavoidable impurity, is preferably completely absent in the soft magnetic stainless steel of the present invention. While the presence of small amounts of S in stainless steel can improve its machinability, in the soft magnetic stainless steel of the present invention, S leads to the precipitation of metal sulfides, which significantly deteriorate the impact toughness and soft magnetic properties of the soft magnetic stainless steel. Therefore, in the soft magnetic stainless steel of the first aspect of the present invention, the content of element S is generally controlled to be below about 0.005% by weight, preferably below about 0.003% by weight.

[0099] Element P, as an unavoidable impurity, is preferably completely absent from the soft magnetic stainless steel of the present invention. Element P is also a harmful residual element in the soft magnetic stainless steel of the present invention, as it adversely affects the corrosion resistance and impact toughness of the soft magnetic stainless steel. Therefore, in the soft magnetic stainless steel of the first aspect of the present invention, the content of element P is generally controlled to be below about 0.005% by weight, preferably below about 0.003% by weight.

[0100] In a second aspect, the present invention also provides a Ta-Cu synergistically strengthened fine-grained high-strength and high-toughness soft magnetic stainless steel profile comprising the Ta-Cu synergistically strengthened fine-grained high-strength and high-toughness soft magnetic stainless steel according to the first aspect of the present invention described above.

[0101] In some embodiments of the soft magnetic stainless steel profile of the second aspect of the present invention, the shape of the profile is not particularly limited; however, in some preferred embodiments, it may be selected from various forms such as bars, wires, coils, plates and / or blocks.

[0102] In a third aspect, the present invention also provides a method for preparing the soft magnetic stainless steel profile described in the second aspect of the present invention. The preparation method of the third aspect of the present invention includes steps 1 to 6.

[0103] Step 1: Casting molten steel

[0104] Step 1 includes providing molten steel containing the elemental composition conforming to the soft magnetic stainless steel as defined in the first aspect of the invention, namely:

[0105] Based on the total weight of the molten steel

[0106] The element Cr content by weight percentage [Cr] is approximately 14.0 to 18.0% by weight.

[0107] The elemental Cu content is approximately 1.5% to 3.0% by weight.

[0108] The element Mo has a weight percentage content of approximately 1.0 to 2.0% [Mo] %.

[0109] The element Ta has a weight percentage content of approximately 0.2 to 0.5% by weight.

[0110] The weight percentage content of element C [C] is about 0.01 to 0.03% by weight;

[0111] The balance is Fe and unavoidable impurities.

[0112] In some preferred embodiments of step 1 above, the weight percentage content of element Ta [Ta] and the weight percentage content of element C [C] in the molten steel further need to meet the following requirements:

[0113] [Ta] + [C] = about 0.2% to about 0.5% by weight, for example, about 0.25% by weight, about 0.35% by weight, or about 0.45% by weight.

[0114] [Ta] : [C] = (16-30):1, for example, 18:1, 25:1 or 28:1.

[0115] In some other preferred embodiments of step 1 above, it is necessary to strictly control the content of elements N, O, S, and P, which are unavoidable impurities in the molten steel. For example, based on the total weight of the molten steel, the elements that are unavoidable impurities are:

[0116] The weight percentage content of N [N] is controlled to be less than about 0.005% by weight, preferably less than about 0.003% by weight; and / or

[0117] The weight percentage content of O is controlled to be less than about 0.005% by weight, preferably less than about 0.003% by weight, more preferably less than about 0.002% by weight, further preferably less than about 0.0015% by weight, and most preferably less than about 0.001% by weight; and / or

[0118] The weight percentage content of S [S] is controlled to be less than about 0.005% by weight, preferably less than about 0.003% by weight; and / or

[0119] The weight percentage content of P is controlled to be less than about 0.005% by weight, preferably less than about 0.003% by weight.

[0120] In step 1 of the method for preparing soft magnetic stainless steel according to the third aspect of the present invention, the molten steel can be obtained by any means known in the art. For example, in a preferred embodiment of the present invention, the molten steel can be obtained by a process commonly used in the art: (1) converter smelting → (2) LF (Ladle Furnace) furnace refining → (3) VD (Vacuum Degassing) and / or RH (Ruhrstahl-Heraeus) furnace vacuum degassing. The molten steel obtained thereby can meet the element content requirements defined in the first aspect of the present invention.

[0121] Molten steel meeting the aforementioned elemental content can be formed into a billet by any method known in the art. For example, it can be formed by ingot casting or continuous casting, preferably by continuous casting. Preferably, the casting temperature during the continuous casting process can be from about 1515°C to about 1535°C, and then air-cooled to a temperature below 40°C, for example, cooled to room temperature.

[0122] There are no particular restrictions on the shape of the resulting billet, which can be determined according to the shape of the final product. For example, depending on the requirements of the final product specifications, it is preferred that the continuous casting billet has a cross-section of about 240 × 240 mm or about 180 × 180 mm, and the billet surface is required to be flat and free of defects visible to the naked eye.

[0123] Step 2: Solution heat treatment

[0124] Step 2 includes solution heat treatment of the billet obtained from Step 1 above.

[0125] The solution heat treatment includes first subjecting the cast billet to a solution heat treatment temperature. The solution is held at a lower temperature for approximately 6 to 10 hours, for example, approximately 6.5 hours, approximately 7 hours, approximately 7.5 hours, approximately 8 hours, approximately 8.5 hours, approximately 9 hours, or approximately 9.5 hours, wherein the solution heat treatment temperature is... This indicates that the value of T1 in °C is rounded up, where

[0126] T1= 1080 + 3550 × [C] + 375 × [Ta];

[0127] in,

[0128] [Ta] represents the weight percentage content of element Ta in the molten steel, expressed as a percentage by weight.

[0129] [C] represents the weight percentage content of element C in the molten steel, expressed as a percentage by weight.

[0130] Here, since the steel grade with the soft magnetic stainless steel composition of the present invention is single-phase ferrite without austenitic phase transformation, the main purpose of solution treatment is to eliminate as-cast segregation and allow various precipitates to dissolve into the ferrite matrix and diffuse uniformly. Therefore, on the one hand, the solution treatment time of the billet should not be too long, for example, not longer than about 10 hours, otherwise it may lead to excessively coarse original grains in the billet and increase costs; nor should it be too short, for example, not shorter than about 6 hours, otherwise various elements may not be able to fully dissolve into the ferrite matrix, affecting the subsequent dispersion precipitation of TaC. On the other hand, the solution heat treatment temperature of the billet is the result calculated by the above formula. The solution heat treatment temperature should not be higher than the calculated result, so as to avoid excessively coarse original grains and increase costs, nor should it be lower than the calculated result, so as to avoid affecting the solution treatment effect of TaC.

[0131] Step 3: Rolling and Cooling

[0132] Step 3 includes rolling the solution-treated billet obtained from Step 2 into a billet, then air-cooling the billet to 780°C to 820°C, and finally cooling it to a temperature below 40°C at a cooling rate of not less than 30°C / s.

[0133] The rolling process can be carried out using rolling mill rolls. The shape of the billet obtained after rolling is not particularly limited, and it can be determined according to the shape required for the next step of cold drawing. For example, it can be in the form of sheet, block, wire, coil and / or bar. In a preferred embodiment of the invention, the shape of the billet is particularly preferably wire or coil.

[0134] During the rolling process, the deformation rate of the cast billet is preferably in the range of about 98% to about 99.5%. The deformation rate is defined as:

[0135] Deformation rate = (Cross-sectional area of ​​billet - Cross-sectional area of ​​billet) / Cross-sectional area of ​​billet × 100%.

[0136] Here, on the one hand, the deformation rate should not be lower than about 98%, otherwise it will be difficult to achieve the effect of breaking the as-cast structure and refining the grains; on the other hand, the deformation rate should not be higher than about 99.5%, otherwise excessive deformation and temperature drop will lead to the risk of the billet cracking.

[0137] Furthermore, during the rolling process, the initial rolling temperature range is preferably from about 1120 to about 1180°C, and the final rolling temperature range is preferably not lower than about 850°C. Here, on the one hand, the initial rolling temperature should not be lower than 1120°C, otherwise it may lead to excessive deformation resistance in the final rolling pass, posing a risk of cracking; on the other hand, the initial rolling temperature should not be higher than about 1180°C, otherwise the billet temperature may be too high, posing a risk of steel sticking. Additionally, no reheating is performed during the rolling process, and the final rolling temperature should not be lower than about 850°C, otherwise it may lead to excessive deformation resistance in the final pass, posing a risk of cracking.

[0138] In addition, after rolling, the billet is air-cooled to a temperature of about 780°C to about 820°C, for example, about 785°C, about 790°C, about 800°C, about 810°C or about 815°C, and finally cooled to a temperature below 40°C at a cooling rate of not less than about 30°C / s, for example, cooled to room temperature. Here, it is preferable to cool to room temperature by water spraying.

[0139] Here, on the one hand, since a certain amount of time needs to be reserved for TaC to fully disperse and precipitate, air cooling is chosen after rolling; on the other hand, when air-cooled to about 780°C to about 820°C or below, the Cu phase will precipitate significantly, increasing the deformation resistance of subsequent cold drawing. Therefore, after air-cooling to about 780°C to about 820°C, it is necessary to cool rapidly to a temperature below 40°C at a cooling rate of not less than 30°C / s, such as cooling to room temperature.

[0140] Step 4: Cold drawing

[0141] Step 4 includes repeatedly cold drawing the rolled and cooled billet obtained from step 3 to obtain a profile.

[0142] The cold drawing process can be carried out using a cold drawing machine. The shape of the profile obtained after cold drawing is not particularly limited and can be determined according to the shape of the final product. For example, it can be in the form of sheet, block, wire, coil, and / or rod. In a preferred embodiment of the invention, the shape of the profile is particularly preferably wire or coil.

[0143] Furthermore, during the cold drawing process, the total elongation μ resulting from multiple cold drawing operations should not be less than approximately 1.4 to avoid insufficient deformation energy storage, which could potentially affect the subsequent recrystallization nucleation rate. Additionally, the total elongation μ should not exceed approximately 1.7, and the elongation coefficient of a single drawing should not exceed approximately 1.2 to prevent breakage or poor profile surface quality. Moreover, no heat treatment is performed during the cold drawing process to avoid premature recrystallization that would deplete the deformation energy storage.

[0144] Step 5: Recrystallization Annealing

[0145] Step 5 includes recrystallizing and annealing the profile obtained from step 4 after cold drawing, and then cooling it to a temperature below 40°C at a cooling rate of not less than 30°C / s.

[0146] The recrystallization annealing process includes first subjecting the cold-drawn profile to recrystallization annealing at a temperature of about 930 to about 970°C (e.g., about 935°C, about 940°C, about 950°C, or about 960°C), and then cooling it to a temperature below about 40°C at a cooling rate of not less than about 30°C / s, for example, cooling it to room temperature, wherein the holding time for the recrystallization annealing is:

[0147] (1) When the cross-sectional area S of the profile is ≤ approximately 100 mm 2 At that time, the holding time for the recrystallization annealing was approximately 5 minutes, and

[0148] (2) When the cross-sectional area S of the profile is greater than approximately 100 mm 2 At that time, the holding time for the recrystallization annealing is ,in, The value of t1 in minutes is rounded up, where

[0149] t1 = 5 + [0.085 × (S - 100)] / μ,

[0150] Where S is in mm 2 The cross-sectional area of ​​the profile is expressed in units of μ; μ is the total elongation coefficient caused by the cold drawing process in step 4.

[0151] Here, after recrystallization annealing, it is preferable to cool the profile rapidly to avoid recrystallization grain growth. Therefore, it needs to be cooled to room temperature at a cooling rate of not less than 30°C / s, for example, by spraying water to cool to room temperature.

[0152] Here, on the one hand, since ferritic stainless steel has a high grain growth tendency, the annealing temperature is preferably not too high, for example, not higher than about 970°C, otherwise the recrystallized grains in the profile may be too coarse, and it is also preferably not too low, for example, not lower than about 930°C, otherwise the Cu element in the profile may dissolve back, relieve stress, and recrystallize incompletely. On the other hand, the annealing time is preferably the result calculated by the above formula, for example, it should not be longer than the result calculated by the above formula, otherwise the recrystallized grains in the profile may be too coarse, and it should not be shorter than the result calculated by the above formula, otherwise the Cu element in the profile may dissolve back, relieve stress, and recrystallize incompletely.

[0153] Step 6: Time-sensitive processing

[0154] Step 6 includes aging the recrystallization annealed profile obtained from step 5 above, and then cooling it to a temperature below 40°C at a cooling rate of not less than 30°C / s, for example, cooling it to room temperature, thereby forming the soft magnetic stainless steel profile.

[0155] The aging treatment includes first subjecting the recrystallized annealed profile to an aging treatment at a temperature of about 600 to about 700°C (e.g., about 615°C, about 630°C, about 640°C, about 650°C, about 660°C, or about 680°C), wherein the holding time for the aging treatment is:

[0156] (1) When the cross-sectional area S of the profile is ≤ approximately 100 mm 2 At that time, the heat preservation time of the aging treatment is ,in The value of t2 in minutes is rounded up, where

[0157] t2 = 75 - T / 10,

[0158] Where T is the holding temperature of the aging treatment, in °C; and

[0159] (2) When the cross-sectional area S of the profile is greater than approximately 100 mm 2 At that time, the heat preservation time of the aging treatment is ,in The value of t3 in minutes is rounded up, where

[0160] t3 = 70 - T / 10 + S / 20

[0161] Where T is the holding temperature of the aging treatment in °C; and S is in mm. 2 The cross-sectional area of ​​the profile is expressed in units of .

[0162] Here, after the aging treatment, it is preferable to cool the profile rapidly to avoid the coarsening and growth of Cu nanoprecipitates. Therefore, it needs to be cooled to room temperature at a cooling rate of not less than 30°C / s, for example, by spraying water to cool to room temperature.

[0163] On the one hand, the aging treatment temperature should not be too high, for example, not higher than about 700°C, otherwise it may lead to an increase in the solid solubility of Cu in the matrix and the amount of Cu-rich phase precipitated will not meet expectations. On the other hand, the aging treatment temperature should not be too low, for example, not lower than about 600°C, otherwise it may lead to the precipitation of too many other harmful phases in the matrix, such as σ phase, Laves phase or Chi phase, thereby deteriorating the plasticity and toughness of the profile. On the other hand, the aging treatment time should preferably not be too long, for example, not longer than the calculation result of the above formula, otherwise it may lead to over-aging of the profile, and the Cu nanoprecipitates will coarsen and grow into Cu-rich phases with other crystal structures, losing their coherent relationship with the ferrite matrix and weakening their strengthening contribution to the matrix. It should also not be too short, for example, not shorter than the calculation result of the above formula, otherwise it may lead to incomplete dispersion precipitation of B2-Cu phase in the profile.

[0164] Furthermore, the soft magnetic stainless steel profile according to the second aspect of the present invention or the soft magnetic stainless steel profile prepared by the preparation method according to the third aspect of the present invention preferably has one or more of the following advantageous properties:

[0165] The yield strength R of the soft magnetic stainless steel profile e For approximately ≥ 650 MPa; and / or

[0166] The tensile strength R of the soft magnetic stainless steel profile m For approximately ≥ 750 MPa; and / or

[0167] The elongation e of the soft magnetic stainless steel profile is approximately ≥ 25%; and / or

[0168] The impact energy (KV2) of the soft magnetic stainless steel profile at -40℃ is approximately ≥ 30 J; and / or

[0169] The saturation magnetic induction intensity B of the soft magnetic stainless steel profile s For approximately ≥ 1.5 T; and / or

[0170] The coercivity H of the soft magnetic stainless steel profile c For approximately ≤ 300 A / m; and / or

[0171] The microstructure of the soft magnetic stainless steel profile contains more than 99.99% ferrite, preferably pure ferrite, and / or

[0172] The effective grain size of the microstructure of the soft magnetic stainless steel profile is approximately ≤ 15 μm.

[0173] In a fourth aspect, the present invention also provides articles made from soft magnetic stainless steel profiles according to the second aspect of the present invention or from soft magnetic stainless steel profiles prepared by the preparation method according to the third aspect of the present invention.

[0174] The present invention will be described in further detail below with reference to specific embodiments and comparative examples.

[0175] In the context of this invention, room temperature is considered to be from about 15 to about 40°C, more preferably about 25°C.

[0176] Examples 1 to 4 and Comparative Examples 1 to 9: General preparation process of soft magnetic stainless steel profiles:

[0177] The process described above as known in the art (1) converter smelting → (2) LF furnace refining → (3) VD and / or RH furnace vacuum degassing provides molten steel that meets the element content requirements of soft magnetic stainless steel as listed in Table 1 of the present invention, Examples 1 to 4 and Comparative Examples 1 to 9.

[0178] The obtained molten steel is continuously cast into square billets with a cross-sectional size of approximately 180 × 180 mm and a length of approximately 6000 mm.

[0179] The billet is subjected to solution heat treatment, the temperature and time of which are shown in Table 2.

[0180] The solution-treated billet is rolled into a wire rod by at least a pair of rotating rolls of a rolling mill, wherein the deformation rate caused by rolling is in the range of about 98% to about 99.5%, and after rolling, it is air-cooled and then air-cooled to room temperature, wherein the temperature before air-cooling and the air-cooling rate are listed in Table 2.

[0181] The cooled billet is cold-drawn multiple times by a cold drawing machine into wire with a cross-sectional diameter of about 12 mm or more, wherein the elongation coefficient caused by a single cold drawing is less than about 1.2. The cross-sectional area of ​​the finished product after cold drawing and the total elongation coefficient caused by cold drawing are shown in Table 2.

[0182] The wire obtained after cold drawing was subjected to recrystallization annealing treatment, the temperature and time of which are shown in Table 2, and then cooled to room temperature by water spraying.

[0183] The annealed wire was subjected to an aging treatment at the temperatures and times shown in Table 2, followed by water cooling to room temperature. This yielded the soft magnetic stainless steel wire rods of the various embodiments and comparative examples.

[0184] Table 1 lists the elemental content ranges (by weight %) of the soft magnetic stainless steel profiles of Examples 1 to 4 and Comparative Examples 1 to 9 of the present invention. The remainder is Fe and other unavoidable impurities. Table 2 lists the specific process parameters used in each step of the method for preparing the soft magnetic stainless steel profiles of Examples 1 to 4 and Comparative Examples 1 to 9.

[0185] Samples of the soft magnetic stainless steel profiles from Examples 1 to 4 and Comparative Examples 1 to 9 of the present invention were taken and their microstructures were observed. Microstructure photographs of the soft magnetic stainless steel wires from Examples 1 to 4 of the present invention are shown in [the original text]. Figures 1 to 4 As shown in the image.

[0186] The room temperature tensile test of the specimens was conducted according to Chinese National Standard GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Test at room temperature". Specifically, the specimens were processed into rod-shaped samples with an original diameter of approximately 3 mm and an original gauge length of approximately 15 mm. The test temperature was controlled at room temperature, and the yield strength R of the soft magnetic stainless steel wires of Examples 1 to 4 and Comparative Examples 1 to 9 was measured. e Tensile strength R m And elongation e.

[0187] The impact test of the specimens was conducted according to the Chinese National Standard GB / T 229-2020 "Metallic Materials - Charpy Pendulum Impact Test Method". Specifically, the specimens were machined into samples with a V-notch and dimensions of approximately 2.5 × 10 × 55 mm. The test temperature was controlled at approximately -40°C, and the impact energy KV2 at -40°C of the soft magnetic stainless steel profiles of Examples 1 to 4 and Comparative Examples 1 to 9 was measured.

[0188] The average grain size of the samples was determined according to the Chinese National Standard GB / T 6394-2017, "Method for Determination of Average Grain Size of Metals". Specifically, the samples were processed into specimens with a size of approximately 10 × 10 mm, and the average grain size of the soft magnetic stainless steels in Examples 1 to 4 and Comparative Examples 1 to 9 was measured using the intercept method.

[0189] The soft magnetic properties of the sample were tested according to the Chinese National Standard GB / T 13012-2008 "Method for Measurement of DC Magnetic Properties of Soft Magnetic Materials". Specifically, the sample was processed into a circular cross-section with dimensions of approximately Φ10 × 200 mm. The test temperature was set to room temperature, and the saturation magnetic induction intensity B of the soft magnetic stainless steels of Examples 1 to 4 and Comparative Examples 1 to 9 was measured. s and coercivity H c .

[0190] Table 3 summarizes the properties of the wires prepared from the soft magnetic stainless steel of Examples 1 to 4 and Comparative Examples 1 to 9 of the present invention.

[0191] Table 1

[0192]

[0193] In Table 1, the symbol "-" indicates "content not detected".

[0194] Table 2

[0195]

[0196] Table 3

[0197]

[0198] As per the appendix to this invention specification Figures 1 to 4 As can be seen from the metallographic images of the samples of Examples 1 to 4 of the present invention, the microstructure of the soft magnetic stainless steel of Examples 1 to 4 of the present invention is ferrite of more than 99.99%, and the structure is uniform, with no micron-level precipitation and no inclusions observed. The grain size is small, which provides a good foundation for the excellent yield strength and ductility of the soft magnetic stainless steel of Examples 1 to 4 of the present invention.

[0199] As can be seen from the performance data of Examples 1 to 4 of the present invention listed in Table 3, the soft magnetic stainless steel samples of Examples 1 to 4 of the present invention all achieved a yield strength of ≥ about 650 MPa, a tensile strength of ≥ about 750 MPa, and an elongation of ≥ about 25%, exhibiting excellent mechanical properties; at the same time, they all achieved an impact energy of ≥ about 30 J at -40℃, demonstrating very good low-temperature toughness; the average grain size of the samples was ≤ about 15 μm, and the saturation magnetic induction intensity B s ≥ Approximately 1.50 T, coercivity H c With a strength of approximately 300 A / m, the soft magnetic stainless steel samples of Examples 1 to 4 of this invention possess excellent soft magnetic properties and can be used to prepare electromagnetic valve devices for mechanical equipment under various complex stresses and extreme climatic conditions.

[0200] As can be seen from the parameters and performance data of Comparative Examples 1 to 9 listed in Tables 1 to 3, the main difference between Comparative Example 1 and Examples 1 to 4 of the present invention is that Cu and Ta elements were not added. Although the sample has good soft magnetic properties, due to the single composition and the absence of Ta to fix C elements and the lack of precipitates pinning grain boundaries, the grains are coarse and the strength and impact toughness are poor. The main difference between Comparative Example 2 and Examples 1 to 4 of the present invention is that Ta elements were not added. Although the precipitation strengthening effect of Cu elements was achieved, the lack of Ta elements to fix C elements and the absence of TaC pinning grain boundaries and dislocations resulted in coarse grains and poor impact toughness and strength. The main difference between Comparative Example 3 and Examples 1 to 4 of the present invention is that Cu elements were not added. Although Ta elements fixed C elements and TaC precipitated to refine the grains, the lack of Cu precipitation strengthening resulted in limited strength improvement. Compared with Examples 1 to 4 of the present invention, the main difference in Comparative Example 4 is that the solid solution temperature was not set according to the calculation formula, resulting in incomplete solid solution of TaC in the grains and insufficient dispersion of precipitation, leading to insignificant grain refinement and relatively poor yield strength and impact toughness. Compared with Examples 1 to 4 of the present invention, the main difference in Comparative Example 5 is that the recrystallization annealing time was not set according to the calculation formula, which led to unnecessary grain growth and weakened strength and impact toughness. Compared with Examples 1 to 4 of the present invention, the main difference in Comparative Example 6 is that the aging time was not set according to the calculation formula, resulting in the coarsening of the Cu-rich phase from the B2-Cu phase to the BCC-Cu and 9R-Cu phases, weakening the aging strengthening effect and resulting in relatively low strength improvement. Compared with Examples 1 to 4 of the present invention, the main difference in Comparative Example 7 is that the [Ta] / [C] ratio is lower than the specified 16:1, resulting in some C elements not being fixed and combining with Cr elements to form a small amount of continuous M at the grain boundaries. 23 The C6 phase worsened the ductility and toughness. Compared with Examples 1 to 4 of the present invention, the main difference in Comparative Example 8 is that the [Ta] / [C] ratio is higher than the specified 30:1, and some Ta and Mo elements combine to form the Chi phase, which worsened the impact toughness. Compared with Examples 1 to 4 of the present invention, the main difference in Comparative Example 9 is that the [Ta]+[C] ratio is higher than the specified 0.5, and excessive TaC clusters aggregate and coarsen, weakening the strength improvement effect and impact toughness.

[0201] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions claimed by the present invention.

Claims

1. A method for preparing fine-grained, high-strength, and high-toughness soft magnetic stainless steel profiles synergistically strengthened by Ta and Cu. The soft magnetic stainless steel profile described herein has one or more of the following properties: The yield strength R of the soft magnetic stainless steel profile e ≥ 650 MPa; The tensile strength R of the soft magnetic stainless steel profile m ≥ 750 MPa; The elongation e of the soft magnetic stainless steel profile is ≥ 25%; The impact energy (KV2) of the soft magnetic stainless steel profile at -40℃ is ≥ 30 J; The saturation magnetic induction intensity B of the soft magnetic stainless steel profile s ≥ 1.50 T; The coercivity H of the soft magnetic stainless steel profile c ≤ 300 A / m; The microstructure of the soft magnetic stainless steel profile contains more than 99.99% ferrite, and The effective grain size of the microstructure of the soft magnetic stainless steel profile is ≤ 15 μm. The method is characterized in that it includes the following steps: Step 1: Provide molten steel and cast it into a billet. The molten steel consists of the elements Cr, Cu, Mo, Ta, C, Fe, and unavoidable impurities. The content of these elements is as follows: Based on the total weight of the molten steel The weight percentage content of element Cr [Cr] is 14.0 to 18.0% by weight. The elemental Cu content (by weight) is 1.5% to 3.0% by weight. The element Mo has a weight percentage content [Mo] of 1.0 to 2.0% by weight. The weight percentage content of element Ta [Ta] is 0.2% to 0.5% by weight. The weight percentage content of element C [C] is 0.01 to 0.03% by weight; And the balance is Fe and unavoidable impurities; Step 2: Perform solution heat treatment on the billet obtained from Step 1; Step 3: Roll the solution-treated billet obtained from Step 2 into a billet and cool it; Step 4: The rolled and cooled billet obtained from Step 3 is subjected to multiple cold drawing to obtain a profile, wherein the total elongation μ resulting from the cold drawing is in the range of 1.4 to 1.7, the elongation resulting from a single cold drawing is not more than 1.2, and no heat treatment is performed during the cold drawing process. Step 5: The profile obtained from step 4 after cold drawing is subjected to recrystallization annealing treatment, and then cooled to a temperature below 40°C at a cooling rate of not less than 30°C / s. Step 6: The recrystallization annealed profile obtained from Step 5 is subjected to aging treatment at a temperature of 600°C to 700°C, and then cooled to a temperature below 40°C at a cooling rate of not less than 30°C / s, thereby forming the soft magnetic stainless steel profile. The holding time for the aging treatment is: (1) When the cross-sectional area S of the profile is ≤ 100 mm 2 At that time, the heat preservation time of the aging treatment is ,in The value of t2 in minutes is rounded up, where t2 = 75-T / 10, Where T is the holding temperature of the aging treatment, in °C; and (2) When the cross-sectional area S of the profile is greater than 100 mm 2 At that time, the heat preservation time of the aging treatment is ,in The value of t3 in minutes is rounded up, where t3 = 70 - T / 10 + S / 20 Where T is the holding temperature of the aging treatment in °C; and S is in mm. 2 The cross-sectional area of ​​the profile is expressed in units of .

2. The method for preparing fine-grained, high-strength, and tough soft magnetic stainless steel profiles with synergistic reinforcement of Ta and Cu according to claim 1, characterized in that, The solution heat treatment time in step 2 is 6 to 10 hours, and the solution heat treatment temperature is... ,in, This indicates that the value of T1 in °C is rounded up, where T1 = 1100 + 2500 × [C] + 312.5 × [Ta]; in, [Ta] represents the weight percentage content of element Ta in the molten steel, expressed as a percentage by weight. [C] represents the weight percentage content of element C in the molten steel, expressed as a percentage by weight.

3. The method for preparing fine-grained, high-strength, and tough soft magnetic stainless steel profiles with synergistic reinforcement of Ta and Cu according to claim 1, characterized in that, In step 3, the total deformation rate caused by rolling is in the range of 98% to 99.5%, the initial rolling temperature is in the range of 1150°C to 1250°C, no reheating is performed during the rolling process, and the final rolling temperature is not lower than 850°C. Then the billet is air-cooled to 780°C to 820°C, and finally cooled to a temperature below 40°C at a cooling rate of not less than 30°C / s.

4. The method for preparing fine-grained, high-strength, and tough soft magnetic stainless steel profiles with synergistic reinforcement of Ta and Cu according to any one of claims 1 to 3, characterized in that, The recrystallization annealing process in step 5 includes holding at a temperature of 930°C to 970°C, and then cooling to a temperature below 40°C at a cooling rate of not less than 30°C / s, wherein the holding time for recrystallization annealing is: (1) When the cross-sectional area S of the profile is ≤ 100 mm 2 At that time, the holding time for the recrystallization annealing was 5 minutes, and (2) When the cross-sectional area S of the profile is greater than 100 mm 2 At that time, the holding time for the recrystallization annealing is ,in, The value of t1 in minutes is rounded up, where t1 = 5 + [0.085 × (S - 100)] / μ, Where S is in mm 2 The cross-sectional area of ​​the profile is expressed in units of μ, which is the total elongation coefficient caused by the cold drawing.

5. A fine-grained, high-strength, and high-toughness soft magnetic stainless steel profile prepared by the method for preparing Ta and Cu synergistically strengthened fine-grained high-strength and high-toughness soft magnetic stainless steel profiles according to any one of claims 1 to 4, characterized in that, The soft magnetic stainless steel profile is composed of the elements Cr, Cu, Mo, Ta, C, Fe, and unavoidable impurities, the content of which is: Based on the total weight of the soft magnetic stainless steel profile: The weight percentage content of element Cr [Cr] is 14.0 to 18.0% by weight. The elemental Cu content (by weight) is 1.5% to 3.0% by weight. The element Mo has a weight percentage content [Mo] of 1.0 to 2.0% by weight. The weight percentage content of element Ta [Ta] is 0.2% to 0.5% by weight. The weight percentage content of element C [C] is 0.01 to 0.03% by weight; The balance is Fe and unavoidable impurities.

6. The soft magnetic stainless steel profile according to claim 5, characterized in that, Based on the total weight of the soft magnetic stainless steel profile, the elements that will be considered as unavoidable impurities are: The weight percentage content of N [N] is controlled below 0.005% by weight; and / or The weight percentage content of O [O] is controlled to be below 0.005% by weight; and / or The weight percentage content of S [S] is controlled below 0.005% by weight; and / or The weight percentage content of P [P] is controlled below 0.005% by weight.

7. The soft magnetic stainless steel profile according to claim 5 or 6, characterized in that, The weight percentage content of element Ta [Ta] and the weight percentage content of element C [C] in the soft magnetic stainless steel profile meet the following requirements: [Ta] + [C] = 0.2-0.5% by weight, and / or [Ta] : [C] = (16-30):

1.

8. An article made from a soft magnetic stainless steel profile according to any one of claims 5 to 7.

9. An article made from a soft magnetic stainless steel profile prepared by the method for preparing a fine-grained, high-strength, and tough soft magnetic stainless steel profile with Ta and Cu synergistic reinforcement according to any one of claims 1 to 4.

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