Nb, Y Composite Low-Temperature Toughness Soft Magnetic Stainless Steel and Soft Magnetic Stainless Steel Profiles and Products Prepared therefrom

Abstract

The present invention belongs to the field of stainless steel. Specifically, the present invention relates to a soft magnetic stainless steel compounded with elements Nb and Y and having excellent low-temperature toughness, and a soft magnetic stainless steel profile and product prepared therefrom. In the present invention, a certain amount of Nb element and Y element compounded in the soft magnetic stainless steel will play a synergistic role, not only enabling the soft magnetic stainless steel to have both excellent low-temperature toughness and soft magnetic properties, but also endowing it with good corrosion resistance and lower raw material costs. The soft magnetic stainless steel profile of the present invention can be effectively applied to solenoid valves and related products serving in low-temperature media, and has good popularization prospects and application values.

Description

Technical Field

[0001] The present invention relates to the technical field of stainless steel. Specifically, the present invention relates to a soft magnetic stainless steel and a soft magnetic stainless steel profile and product prepared therefrom. Background Art

[0002] With the development of intelligent products, devices using electromagnetic force as switching elements and control units have become indispensable in various fields, such as brakes, relays, solenoid valves, etc. There is an increasingly urgent need for high-quality soft magnetic stainless steel for solenoid valve cores with high magnetic induction, low coercivity, and at the same time having mechanical properties such as corrosion resistance, wear resistance, and impact resistance.

[0003] However, generally speaking, the quality of the soft magnetic stainless steel available on the market at present cannot meet some specific industrial needs. For example, they generally have poor low-temperature toughness, which may lead to a short service life of the products made therefrom, especially prone to gas or liquid leakage in the solenoid valves made therefrom.

[0004] Regarding the composition design of soft magnetic stainless steel, Chinese Patent Application CN114836684A with the invention name of "Low-chromium Soft Magnetic Stainless Steel and Its Preparation Method and Application" discloses a low-chromium soft magnetic stainless steel, and its alloy element composition by weight percentage is: C: ≤0.015%, Si: 0.4% - 1.0%, Mn: 0.15% - 0.30%, P: ≤0.030%, S: ≤0.005%, Cr: 11.0% - 13.5%, Ni: ≤0.20%, Ti: 0.12% - 0.30%, N: ≤0.020%, and the balance is Fe and inevitable impurities. This patent application obtains stainless steel with a relatively high saturation magnetic induction intensity through the design of element content and the optimization of the preparation process. However, the inclusion and precipitation content of the soft magnetic stainless steel in this patent application is relatively high, and the soft magnetic properties and low-temperature toughness still need to be further improved.

[0005] Chinese Patent Application CN114606440A with the invention name of "A High-performance Soft Magnetic Stainless Steel and Its Preparation Method" discloses a soft magnetic stainless steel, and its alloy element composition by weight percentage is: C: ≤0.02%, Si: 1.5 - 2.5%, Mn: ≤0.8%, P: ≤0.03%, S: 0.15 - 0.35%, Ni: ≤0.4%, Cr: 13.0 - 15.0%, N: ≤0.02%, Mo: 0.2 - 0.8%, Nb: 0.15 - 0.30%, Re: 0.005 - 0.012%, and the rest is iron and inevitable impurities. This patent application obtains stainless steel with excellent soft magnetic properties and cutting properties by adding Nb element and optimizing the metallurgical process. However, the soft magnetic stainless steel in this patent application has poor plastic toughness, especially low-temperature toughness, which limits its industrial application scenarios.

[0006] Chinese patent application CN114871270A, entitled "A high-speed wire rolling method for soft magnetic stainless steel wire rod", discloses a high-speed wire rolling method for soft magnetic stainless steel wire rod. The patent application improves the rolling yield of soft magnetic stainless steel wire rod by subjecting the billet to multi-stage heating and controlling the temperature nodes during the rolling process of the method. However, the method of the patent application does not include an annealing process, resulting in low low-temperature impact toughness of the final product.

[0007] In summary, the low-temperature impact toughness of the soft magnetic stainless steel in the prior art is still relatively low. Therefore, it is necessary to further research and develop soft magnetic stainless steel profiles with excellent low-temperature toughness and electromagnetic properties to meet the use requirements of electromagnetic valve cores that can serve in low-temperature media. Summary of the invention

[0008] Object of the Invention

[0009] In view of the problems existing in the prior art described in the above background technology section, an object of the present invention is to provide a soft magnetic stainless steel having excellent low temperature toughness and electromagnetic properties and a soft magnetic stainless steel profile and product prepared therefrom.

[0010] Technical Solution

[0011] In order to achieve the above-mentioned purpose of the present invention, the present invention provides the following technical solutions:

[0012] Solution 1: A soft magnetic stainless steel, the soft magnetic stainless steel consisting of the following elements:

[0013] Based on the total weight of the soft magnetic stainless steel:

[0014] about 15.0 to about 17.0 wt. %, preferably about 15.5 to about 16.5 wt. % Cr;

[0015] about 0.03 to about 0.30 wt. %, preferably about 0.05 to about 0.20 wt. % Nb;

[0016] about 0.01 to about 0.10 wt %, preferably about 0.015 to about 0.05 wt % of Y;

[0017] and the balance Fe; and

[0018] Unavoidable impurities.

[0019] Solution 2: The soft magnetic stainless steel according to Solution 1, wherein the elements as the unavoidable impurities are based on the total weight of the soft magnetic stainless steel:

[0020] The content of C is controlled to be below about 0.015 wt%, preferably below about 0.010 wt%; and / or

[0021] The content of N is controlled to be below about 0.005 wt%, preferably below about 0.003 wt%; and / or

[0022] The content of O is controlled to be below about 0.002 wt%, preferably below about 0.0015 wt%; and / or

[0023] The content of S is controlled to be below about 0.005 wt%, preferably below about 0.003 wt%; and / or

[0024] The content of P is controlled to be below about 0.005 wt%, preferably below about 0.003 wt%.

[0025] Solution 3: A soft magnetic stainless steel profile prepared from the soft magnetic stainless steel according to Solution 1 or 2 above, preferably a wire.

[0026] Solution 4: The soft magnetic stainless steel profile according to Solution 3 above, wherein the soft magnetic stainless steel profile has any one or more of the following properties:

[0027] The -40°C impact energy KV2 of the soft magnetic stainless steel profile is about ≥45 J;

[0028] The saturation magnetic induction strength B of the soft magnetic stainless steel profile s is about ≥1.6 T;

[0029] The coercivity H of the soft magnetic stainless steel profile c is about ≤130 A / m;

[0030] The remanent magnetic induction strength B of the soft magnetic stainless steel profile r is about ≤0.3 T;

[0031] The microstructure of the soft magnetic stainless steel profile contains more than about 99.99% ferrite, preferably pure ferrite, and

[0032] The effective grain size of the microstructure of the soft magnetic stainless steel profile is about ≤30 μm.

[0033] Solution 5: A method for preparing the soft magnetic stainless steel profile according to Solution 3 or 4 above, wherein the method comprises the following steps:

[0034] Step 1: Provide molten steel containing the element contents as contained in the soft magnetic stainless steel defined in Solution 1 or 2 above;

[0035] Step 2: Form the molten steel obtained in Step 1 into a slab;

[0036] Step 3: Rolling the billet obtained from Step 2 into profiles, and

[0037] Step 4: Annealing the rolled profiles obtained from Step 3 to form the soft magnetic stainless steel profiles.

[0038] Solution 6: The preparation method according to Solution 5 above, wherein the rolling process in Step 3 includes: first holding the billet at a temperature of about 1060 to about 1140 °C for about 0.5 to about 1 hour; then rolling the billet, wherein the starting rolling temperature is controlled within the range of about 1020 to about 1080 °C, and the finishing rolling temperature is controlled within the range of about 720 to about 780 °C; and finally cooling the rolled profiles to room temperature at a cooling rate of not less than about 8 °C / s.

[0039] Solution 7: The preparation method according to Solution 5 or 6 above, wherein the annealing process in Step 4 includes: first holding the rolled profiles at a temperature of about 900 to about 950 °C for about 4 to about 6 minutes, and then cooling the profiles to room temperature at a cooling rate of not less than about 20 °C / s.

[0040] Solution 8: An article prepared from the soft magnetic stainless steel profiles according to Solution 3 or 4 above or from the soft magnetic stainless steel profiles prepared by the preparation method according to any one of Solutions 5 to 7 above.

[0041] Solution 9: The article according to Solution 8 above, wherein the article is selected from brakes, relays, and solenoid valves.

[0042] Technical Effect

[0043] Compared with the prior art, the soft magnetic stainless steel of the present invention and the profiles prepared therefrom achieve the following technical effects:

[0044] The soft magnetic stainless steel profiles of the present invention have excellent low-temperature toughness and also have excellent soft magnetic properties, such as a higher saturation magnetic induction intensity, a lower coercive force, and a lower residual magnetic induction intensity.

[0045] Specifically, the soft magnetic stainless steel of the present invention adopts a reasonable chemical composition design, optimizes and excludes various alloying elements in other soft magnetic stainless steels, retains the Cr element, strictly controls the contents of impurity elements such as C, N, O, S, and P, so as to fully ensure that the steel has excellent soft magnetic properties, and uses the Nb and Y elements to compound and optimize the microalloy precipitation, thereby obtaining a suitable fine grain size, making the soft magnetic stainless steel of the present invention have excellent low-temperature toughness at the same time. The excellent low-temperature impact toughness and soft magnetic properties of the soft magnetic stainless steel of the present invention are specifically manifested as: the impact energy KV2 at -40 °C ≥ 45 J, the saturation magnetic induction intensity B s ≥ 1.6 T, the coercive force Hc ≤130 A / m, the remanent magnetic induction intensity B r ≤0.3 T.

[0046] The soft magnetic stainless steel profile of the present invention can be effectively applied to the solenoid valve cores and related products serving in low-temperature media, and has very good popularization prospects and application values.

[0047] In addition, the soft magnetic stainless steel of the present invention does not use expensive Ni and Mo elements. The alloying elements are only Cr element not higher than about 17% and trace amounts of Nb and Y elements, and the preparation process is simple and conventional, having relatively low alloy costs and preparation costs.

[0048] In the preparation method of the present invention, by adding Nb and Y elements and optimizing the annealing process, the structure of the soft magnetic stainless steel of the present invention is uniform, thus having good plasticity and being beneficial to the downstream drawing process. Brief Description of the Drawings

[0049] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for use in the specific embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0050] Figure 1 It is the metallographic structure photo of the soft magnetic stainless steel profile of Example 1 of the present invention.

[0051] Figure 2 It is the metallographic structure photo of the soft magnetic stainless steel profile of Example 2 of the present invention.

[0052] Figure 3 It is the metallographic structure photo of the soft magnetic stainless steel profile of Example 3 of the present invention. Detailed Description of the Embodiments

[0053] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually in accordance with conventional conditions.

[0054] The endpoints and any values within the ranges disclosed in the present invention are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. The term "about" used in the present invention means that the number it modifies can fluctuate within the range of ±20%, ±15%, ±10%, ±5% or ±2% of that number. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0055] In a first aspect of the present invention, the present invention provides a soft magnetic stainless steel. The soft magnetic stainless steel according to the first aspect of the present invention is composed of the following elements:

[0056] Based on the total weight of the soft magnetic stainless steel:

[0057] About 15.0 to about 17.0% by weight, preferably about 15.5 to about 16.5% by weight of Cr (chromium);

[0058] About 0.03 to about 0.30% by weight, preferably about 0.05 to about 0.20% by weight of Nb (niobium);

[0059] About 0.010 to about 0.100% by weight, preferably about 0.015 to about 0.050% by weight of Y (yttrium);

[0060] And the balance of Fe (iron); and

[0061] Inevitable impurities.

[0062] In the soft magnetic stainless steel according to the first aspect of the present invention above, the Cr element is an element that promotes the formation of a ferrite structure and is also the main element that makes the stainless steel not easily rust. 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 the corrosion resistance also improves. However, as the Cr content increases, the saturation magnetization intensity of the material decreases. Therefore, in the soft magnetic stainless steel of the present invention, the content of the element Cr should be controlled within the range of about 15 to about 17% by weight. For example, it can be set to about 15.5% by weight, about 16% by weight or about 16.5% by weight.

[0063] In the soft magnetic stainless steel of the first aspect of the present invention described above, the Nb element is a strong ferrite-forming element and also a strong carbide and nitride-forming element. The Nb element can form carbides and nitrides with the residual C and N in the stainless steel, inhibit the precipitation of carbides and nitrides formed by Cr in the stainless steel, and enhance the intergranular corrosion resistance of the stainless steel. The precipitates of Nb can also pin the grain boundaries, inhibit grain growth, play a role in refining grains, and improving impact toughness. However, too much Nb element results in too fine grains and too high coercivity of the soft magnetic stainless steel. Therefore, in the soft magnetic stainless steel of the present invention, the content of the element Nb should be controlled within the range of about 0.03 to about 0.3 wt%, for example, it can be set to about 0.05 wt%, about 0.10 wt%, about 0.15 wt%, about 0.20 wt% or about 0.25 wt%.

[0064] In the soft magnetic stainless steel of the first aspect of the present invention described above, the Y element will interact with possible low melting point harmful impurity elements, inhibit their segregation at the grain boundaries, and play a role in purifying and strengthening the grain boundaries. In addition, the Y element can effectively improve the morphology and distribution of inclusions in the steel, reduce the number of irregular large-sized inclusions in the steel, and thus improve the plasticity of the steel. However, the content of the Y element should not be too high either. Excessive Y element will instead make the inclusions coarser and increase the brittleness tendency, so it needs to be controlled within a certain range. Therefore, in the soft magnetic stainless steel of the present invention, the content of the element Y should be controlled within the range of about 0.01 to about 0.1 wt%, for example, it can be set to about 0.015 wt%, about 0.02 wt%, about 0.03 wt%, about 0.04 wt%, about 0.05 wt%, about 0.06 wt%, about 0.07 wt%, about 0.08 wt% or about 0.09 wt%.

[0065] Furthermore, in the soft magnetic stainless steel of the first aspect of the present invention described above, the combined addition of the Nb element and the Y element will produce a synergistic effect, optimize the precipitation form of NbC in the stainless steel, increase the nucleation number of M7C3-type carbides, promote the refinement of the precipitation phase of Nb in the ferrite, disperse precipitation, enhance the grain refinement and precipitation strengthening effects, and thus synergistically improve the low-temperature impact toughness of the soft magnetic stainless steel.

[0066] In some preferred embodiments of the soft magnetic stainless steel of the first aspect of the present invention described above, it is preferred to strictly control the contents of the elements C (carbon), N (nitrogen), O (oxygen), S (sulfur), and P (phosphorus) as inevitable impurities.

[0067] Element C, as an inevitable impurity, is preferably completely absent from the soft magnetic stainless steel of the present invention. Element C is a strong austenite-forming element, which is not conducive to the formation of ferrite. Element C has a large affinity with element Cr and will form cementite-type carbides, which have an adverse effect on the magnetic properties of stainless steel, may reduce the magnetic induction intensity and magnetic permeability, and increase magnetic loss and coercivity. Therefore, in the soft magnetic stainless steel of the first aspect of the present invention, the content of C is usually controlled below about 0.015 wt%, preferably below about 0.010 wt%, and more preferably below about 0.005 wt%.

[0068] Element N, as an inevitable impurity, is preferably completely absent from the soft magnetic stainless steel of the present invention. Element N is roughly the same as element C in many properties. Element N is also a strong austenite-forming element and has an adverse effect on the magnetic properties of ferritic stainless steel. In addition, the solubility of N is relatively low, and it is very easy to precipitate after forming nitrides with other alloying elements, causing local distortion inside the stainless steel, forming a stress field, hindering the movement of domain walls, increasing magnetic loss, and weakening the magnetic induction intensity and magnetic permeability. Therefore, in the soft magnetic stainless steel of the first aspect of the present invention, the content of element N is usually controlled below about 0.005 wt%, preferably below about 0.003 wt%.

[0069] Element O, as an inevitable 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 in the form of oxide inclusions with other alloying elements during the smelting process, greatly 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 O is usually controlled below about 0.002 wt%, preferably below about 0.0015 wt%, and more preferably below about 0.001 wt%.

[0070] Element S, as an inevitable impurity, is preferably completely absent from the soft magnetic stainless steel of the present invention. Although the small presence of element S in stainless steel can improve the cutting performance of the stainless steel, in the soft magnetic stainless steel of the present invention, element S will cause the precipitation of metal sulfides, which will 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 S is usually controlled below about 0.005 wt%, preferably below about 0.003 wt%.

[0071] Element P, as an inevitable impurity, is preferably completely absent in 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, and element P will have an adverse effect on 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 P is usually controlled to be below about 0.005 wt%, preferably below about 0.003 wt%.

[0072] In the second aspect of the present invention, the present invention provides a soft magnetic stainless steel profile prepared from the soft magnetic stainless steel of the first aspect of the present invention as described above.

[0073] In some preferred embodiments of the soft magnetic stainless steel profile of the second aspect of the present invention as described above, the shape of the profile is not particularly limited. However, in some preferred embodiments, it can be selected from various forms such as bars, wires, wire rods, plates and / or blocks, etc.

[0074] In some other preferred embodiments of the soft magnetic stainless steel profile of the second aspect of the present invention as described above, the soft magnetic stainless steel profile of the present invention can have any one or more of the following properties, more preferably all:

[0075] The -40 °C impact energy KV2 of the soft magnetic stainless steel profile is about ≥45 J; and / or

[0076] The saturation magnetic induction strength B of the soft magnetic stainless steel profile s is about ≥1.6 T; and / or

[0077] The coercivity H of the soft magnetic stainless steel profile c is about ≤130 A / m; and / or

[0078] The remanent magnetic induction strength B of the soft magnetic stainless steel profile r is about ≤0.3 T; and / or

[0079] The microstructure of the soft magnetic stainless steel profile contains more than 99.99% ferrite, preferably pure ferrite, and / or

[0080] The effective grain size of the microstructure of the soft magnetic stainless steel profile is about ≤30 μm.

[0081] In the third aspect of the present invention, the present invention provides a method for preparing the soft magnetic stainless steel profile of the second aspect of the present invention as described above.

[0082] The preparation method of the third aspect of the present invention as described above includes the following steps 1 to 4.

[0083] Step 1 includes providing molten steel, which contains the element contents of the soft magnetic stainless steel conforming to the definition of the first aspect of the present invention:

[0084] Based on the total weight of the soft magnetic stainless steel:

[0085] about 15.0 to about 17.0 wt%, preferably about 15.5 to about 16.5 wt% of Cr;

[0086] about 0.03 to about 0.30 wt%, preferably about 0.05 to about 0.20 wt% of Nb;

[0087] about 0.010 to about 0.100 wt%, preferably about 0.015 to about 0.050 wt% of Y;

[0088] and the balance Fe; and

[0089] inevitable impurities.

[0090] In some preferred embodiments of the method for preparing a soft magnetic stainless steel profile according to the third aspect of the present invention above, it is necessary to strictly control the contents of elements C, N, O, S and P as inevitable impurities in the molten steel. For example, based on the total weight of the molten steel, the elements as the inevitable impurities:

[0091] the content of C is controlled to be below about 0.015 wt%, preferably below about 0.010 wt%; and / or

[0092] the content of N is controlled to be below about 0.005 wt%, preferably below about 0.003 wt%; and / or

[0093] the content of O is controlled to be below about 0.002 wt%, preferably below about 0.0015 wt%; and / or

[0094] the content of S is controlled to be below about 0.005 wt%, preferably below about 0.003 wt%; and / or

[0095] the content of P is controlled to be below about 0.005 wt%, preferably below about 0.003 wt%.

[0096] In step 1 of the method for preparing a soft magnetic stainless steel profile according to the third aspect of the present invention above, the molten steel can be obtained by any known means in the art. For example, in a preferred embodiment of the present invention, the molten steel can be obtained by the process of (1) converter smelting → (2) LF (Ladle Furnace) refining → (3) VD (Vacuum Degassing) and / or RH (Ruhrstahl-Heraeus) furnace vacuum degassing commonly used in the art. The molten steel thus obtained can meet the requirement range of the element content of the stainless steel according to the first aspect of the present invention above.

[0097] Step 2 includes forming the molten steel obtained from step 1 above into a slab.

[0098] In step 2 of the method for preparing the soft magnetic stainless steel profile described in the third aspect of the present invention above, the forming can be carried out by any known means in the art. For example, die casting or continuous casting can be employed, and preferably continuous casting is used to implement the forming in step 2. Preferably, the casting temperature during the continuous casting process can be about 1515 °C to about 1535 °C.

[0099] The shape of the obtained billet is not particularly limited and can be determined according to the shape of the finally formed product. For example, according to the requirements of the specifications of the product to be finally formed, preferably the shape of the continuous casting billet is a billet with a cross-section of about 240×240 mm or about 180×180 mm, and the surface of the billet is required to be flat without visible defects to the naked eye.

[0100] In step 2 of the method for preparing the soft magnetic stainless steel profile described in the third aspect of the present invention above, the temperature of the billet is preferably maintained above about 1200 °C, more preferably about 1200 to about 1250 °C. Such a temperature can ensure that the subsequent rolling process can proceed smoothly and ensure that the final profile has ideal properties.

[0101] Step 3 includes rolling the billet obtained from step 2 above into a profile.

[0102] The rolling process can be carried out by a rolling mill using rolls. The shape of the profile obtained after rolling is not particularly limited and can be determined according to the shape of the finally formed product. For example, it can be in the form of a sheet, block, wire, coil, and / or rod. In a preferred embodiment of the present invention, the shape of the profile is particularly preferably a wire or a coil.

[0103] In a preferred embodiment of step 3 of the method for preparing the soft magnetic stainless steel profile described in the third aspect of the present invention above, first, the billet is maintained at a temperature of about 1060 to about 1140 °C (such as about 1070 °C, about 1080 °C, about 1090 °C, about 1100 °C, about 1110 °C, about 1120 °C, or about 1130 °C) for about 0.5 to about 1 hour (such as about 0.6 hour, about 0.7 hour, about 0.8 hour, or about 0.9 hour); then the billet is rolled, wherein the starting rolling temperature is controlled within the range of about 1020 to about 1080 °C (such as about 1025 °C, about 1030 °C, about 1040 °C, about 1050 °C, about 1060 °C, or about 1070 °C), and the finishing rolling temperature is controlled within the range of about 720 to about 780 °C (such as about 740 °C, about 760 °C, or about 770 °C).

[0104] Here, since the phase diagram of the steel grade with the soft magnetic stainless steel composition of the present invention is single-phase ferrite and there is no austenite phase transformation, on the one hand, the setting of these parameters is based on the parameters in the prior art, and on the other hand, it is determined by the inventors of the present invention through experiments. For example, on the one hand, the holding temperature of the slab is preferably not too high or too low. For example, it is preferably not higher than about 1140 °C, otherwise the original grains in the slab may be too coarse, and it is also preferably not lower than about 1060 °C, otherwise the deformation resistance of the slab may be too large and cracking may occur during rolling; on the other hand, the holding time of the slab is preferably not too long or too short. For example, it is preferably not longer than about 1 hour, otherwise the original grains in the slab may be too coarse, and it is also preferably not shorter than about 0.5 hour, otherwise a temperature difference may exist between the inside and outside of the slab and cracking may occur during rolling; on the other hand, the starting rolling temperature is preferably not too high or too low. For example, it is preferably not higher than about 1080 °C, otherwise the original grains of the slab during rolling may be too coarse or even cause a steel piling accident, and it is also preferably not lower than about 1020 °C, otherwise the deformation resistance of the slab may be too large and cracking may occur during rolling; finally, the finishing rolling temperature is preferably not too high or too low. For example, it is preferably not higher than about 780 °C, otherwise the grains in the rolled profile may be too large, and it is also preferably not lower than about 720 °C, otherwise hot rolling cracks may appear in the profile.

[0105] In addition, the profile obtained after the rolling may not be cooled and directly subjected to annealing heating operation. However, the phase diagram of the steel grade with the soft magnetic stainless steel composition of the present invention is all ferrite and there is no austenite phase transformation. At the same time, the ferrite grains have a high tendency to grow at high temperatures. Therefore, in order to avoid grain coarsening, it is generally preferred to first cool the profile and then perform recrystallization annealing. For example, in a preferred embodiment of the present invention, in order to cool the profile to room temperature as soon as possible, it can be air-cooled to room temperature at a cooling rate of not less than 8 °C / s, which can also facilitate subsequent operations such as the transfer of the profile. The cooling rate of the profile here should not be too slow. For example, it should not be lower than about 8 °C / s, otherwise the grains and precipitates in the profile may grow.

[0106] Step 4 includes annealing the rolled profile obtained from the above step 3 to form the soft magnetic stainless steel profile.

[0107] There are no particular limitations on the specific parameters of the annealing treatment, as long as this annealing treatment can endow the soft magnetic stainless steel profile of the present invention with the advantageous properties described herein. However, in a preferred embodiment, in step 4 of the preparation method described in the third aspect of the present invention above, the annealing treatment includes first maintaining the rolled profile at a temperature of about 900 to about 950 °C (such as about 910 °C, about 920 °C, about 930 °C or about 940 °C) for about 4 to about 6 minutes (such as about 5 minutes), and then quickly cooling the profile to room temperature. Here, it is preferred to quickly cool the profile after recrystallization annealing to avoid the growth of recrystallized grains. For example, it can be cooled to room temperature at a cooling rate of not less than 20 °C / s. For example, it can be cooled to room temperature by spraying water.

[0108] Here, on the one hand, the temperature of the annealing treatment is preferably not too high or too low. For example, it is not preferably higher than about 950 °C, otherwise the recrystallized grains in the profile may be too coarse. Nor is it preferably lower than about 900 °C, otherwise the stress relief and recrystallization of the profile may be incomplete. On the other hand, the annealing time is preferably not too long or too short. For example, it is not preferably longer than about 6 minutes, otherwise the recrystallized grains in the profile may be too coarse. Nor is it preferably shorter than about 4 minutes, otherwise the stress relief and recrystallization of the profile may be incomplete.

[0109] Preferably, after the annealing treatment as described above, the obtained soft magnetic stainless steel profile preferably has one or more of the following advantageous properties:

[0110] The impact energy KV2 of the soft magnetic stainless steel profile at -40 °C is about ≥45 J; and / or

[0111] The saturation magnetic induction intensity B of the soft magnetic stainless steel profile s is about ≥1.6 T; and / or

[0112] The coercivity H of the soft magnetic stainless steel profile c is about ≤130 A / m; and / or

[0113] The remanent magnetic induction intensity B of the soft magnetic stainless steel profile r is about ≤0.3 T; and / or

[0114] The microstructure of the soft magnetic stainless steel profile contains more than 99.99% ferrite, preferably pure ferrite, and / or

[0115] The effective grain size of the microstructure of the soft magnetic stainless steel profile is about ≤30 μm.

[0116] In the fourth aspect of the present invention, the present invention provides a soft magnetic stainless steel product, which is prepared from the soft magnetic stainless steel profile of the second aspect of the present invention as described above.

[0117] Particularly preferably, the soft magnetic stainless steel products of the fourth aspect of the present invention are brakes, relays, and solenoid valves containing soft magnetic stainless steel profiles.

[0118] The present invention will be further described in detail below in conjunction with specific examples and comparative examples.

[0119] In the context of the present invention, room temperature is considered to be about 15 to about 40 °C, more preferably about 25 °C.

[0120] Examples 1-3 and Comparative Examples 1-5: General preparation process of soft magnetic stainless steel profiles:

[0121] The molten steel meeting the requirements of the soft magnetic stainless steel element content ranges listed in Table 1 below for Examples 1-3 and Comparative Examples 1-5 of the present invention is provided through the processes of (1) converter smelting → (2) LF furnace refining → (3) VD and / or RH furnace vacuum degassing as known in the art (as shown in Table 1).

[0122] The obtained molten steel is continuously cast into a square billet with a specification of about 180×180×6000 mm, and the holding temperature and time of the billet are as shown in Table 2.

[0123] The heat-insulated billet is rolled into a profile through at least a pair of rotating rolls of a rolling mill. The profile is a wire with a cross-sectional diameter in the range of about 10 to about 20 mm, and the starting rolling temperature and the final rolling temperature of the rolling process are listed in Table 2.

[0124] The rolled wire is air-cooled to room temperature, and the cooling rate is as shown in Table 2.

[0125] The cooled wire undergoes an annealing treatment, which includes first holding the wire at the temperature shown in Table 2 for several minutes, and then spraying water to cool it to room temperature to obtain the soft magnetic stainless steel wire rods of each example and comparative example.

[0126] Table 1 lists the element content ranges (weight %, the rest being Fe and other inevitable impurities) contained in the soft magnetic stainless steel profiles of Examples 1-3 and Comparative Examples 1-5 of the present invention. Table 2 lists the specific process parameters adopted in each step in the method for preparing the soft magnetic stainless steel profiles of Examples 1-3 and Comparative Examples 1-5.

[0127] Samples of the soft magnetic stainless steel profiles of Examples 1-3 and Comparative Examples 1-5 of the present invention are taken, and their microstructures are observed. The microstructural photos of the soft magnetic stainless steel wires of Examples 1-3 of the present invention are respectively shown in Figures 1-3 as follows.

[0128] The impact test of the specimen was carried out according to the Chinese national standard GB / T 229-2020 "Test method for Charpy pendulum impact test of metallic materials". Specifically, the specimen was processed into a sample with a V-notch and dimensions of approximately 2.5×10×55 mm, the test temperature was controlled at approximately -40 °C, and the -40 °C impact energy KV2 of the soft magnetic stainless steels of Examples 1-3 and Comparative Examples 1-5 was measured.

[0129] The average grain size of the specimen was determined according to the Chinese national standard GB / T 6394-2017 "Method for determination of average grain size of metals". Specifically, the specimen was processed into a sample with dimensions of approximately 10×10 mm, and the average grain size of the soft magnetic stainless steels of Examples 1-3 and Comparative Examples 1-5 was measured using the intercept method.

[0130] The soft magnetic properties of the specimen were tested according to the Chinese national standard GB / T 13012-2008 "Measurement method for DC magnetic properties of soft magnetic materials". Specifically, the specimen was processed into a sample with a circular cross-section and dimensions of approximately Φ10×200 mm, the test temperature was set at room temperature, and the saturation magnetic induction intensity B s , coercivity H c and residual magnetic induction intensity B r .

[0131] Table 3 summarizes the various properties of the wire rods prepared from the soft magnetic stainless steels of Examples 1-3 and Comparative Examples 1-5 of the present invention.

[0132] Table 1

[0133]

[0134] Table 2

[0135]

[0136] Table 3

[0137]

[0138] From the metallographic structure pictures of the specimens of Examples 1-3 of the present invention shown in the attached Figures 1-3 drawings of the specification of the present invention, it can be seen that the microstructures of the soft magnetic stainless steels of Examples 1-3 of the present invention are all ferrite with more than 99.99%, and the structures are uniform, no micron-scale precipitation is observed and there are no inclusions, which indicates that the soft magnetic stainless steels of Examples 1 to 3 of the present invention have excellent plastic toughness and excellent soft magnetic properties.

[0139] From the performance data of Examples 1-3 of the present invention listed in Table 3, it can be seen that the soft magnetic stainless steel specimens of Examples 1 to 3 of the present invention have all achieved an impact energy of ≥45 J at -40 °C, showing very excellent low-temperature toughness; the average grain size of the specimens is ≤30 μm, and the saturation magnetic induction intensity B s ≥1.6 T, and the coercivity H c ≤130 A / m, and the remanent magnetic induction intensity B r ≤0.3 T. Therefore, the soft magnetic stainless steel specimens of Examples 1-3 of the present invention have excellent soft magnetic properties and can be used to prepare solenoid valve devices for various mechanical equipment.

[0140] From the various parameters and performance data of Comparative Examples 1-5 listed in Tables 1-3, it can be seen that compared with Examples 1-3 of the present invention, the main differences in Comparative Examples 1-3 are that the Nb and / or Y elements are not added, which affects the morphology and distribution of the precipitates in the stainless steel, weakens the effect of the dispersed distribution of the precipitates pinning the grain boundaries, and the increased precipitate inclusions and element segregation at the grain boundaries not only lead to an increase in grain size and a decrease in low-temperature toughness, but also affect the rotation of magnetic domains, deteriorating the coercivity and remanent magnetic induction intensity of the steel, and the effect of single addition of Nb and Y elements on refining grains and precipitates is not as good as that of composite addition; compared with Examples 1-3 of the present invention, the main differences in Comparative Examples 4-5 are that the common Al and / or Si elements in the field of soft magnetic stainless steel are added, which affects the morphology and recovery effect of the recrystallized grains in the stainless steel, promotes the aggregation and growth of precipitate inclusions in the grains, and the increased precipitate inclusions and non-equiaxed coarse grains not only greatly reduce the low-temperature toughness, but also affect the rotation of magnetic domains, deteriorating the coercivity and remanent magnetic induction intensity of the steel. The addition of Al and Si as impurity elements in the soft magnetic stainless steel of the present invention will significantly coarsen the grains, and the size of the precipitate inclusions will increase significantly, and the low-temperature impact toughness will deteriorate significantly.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions required to be protected by the present invention.

Claims

1. A soft magnetic stainless steel profile, characterized in that: The soft magnetic stainless steel profile is prepared from the following soft magnetic stainless steel, and the soft magnetic stainless steel is composed of the following elements: Based on the total weight of the soft magnetic stainless steel: 15.0 to 17.0 wt. % Cr; 0.03 to 0.30 wt. % Nb; 0.01 to 0.10 wt % Y; and the balance Fe; and Unavoidable impurities; The soft magnetic stainless steel profile has the following properties: The -40°C impact energy KV2 of the soft magnetic stainless steel profile is ≥ 45 J; The saturation magnetic induction intensity B of the soft magnetic stainless steel profile s ≥ 1.6 T; The coercive force H of the soft magnetic stainless steel profile c ≤ 130 A / m; The residual magnetic induction intensity B of the soft magnetic stainless steel profile r ≤ 0.3 T; The microstructure of the soft magnetic stainless steel profile contains more than 99.99% ferrite; The effective grain size of the microstructure of the soft magnetic stainless steel profile is ≤ 30 μm; The method for preparing the soft magnetic stainless steel profile comprises the following steps: Step 1: providing molten steel, wherein the molten steel contains an element content consistent with that contained in the soft magnetic stainless steel; Step 2: forming the molten steel obtained in step 1 into a casting billet; Step 3: rolling the cast billet obtained in step 2 into a profile, the rolling process comprising: firstly keeping the cast billet at a temperature of 1060 to 1140° C. for 0.5 to 1 hour; then rolling the cast billet, wherein the start rolling temperature is controlled within the range of 1020 to 1080° C., and the final rolling temperature is controlled within the range of 720 to 780° C.; and finally cooling the rolled profile to room temperature at a cooling rate of not less than 8° C. / s; Step 4: The rolled profile obtained in step 3 is annealed to form the soft magnetic stainless steel profile, and the annealing process includes: first, keeping the rolled profile at a temperature of 900 to 950°C for 4 to 6 minutes, and then cooling the profile to room temperature at a cooling rate of not less than 20°C / s.

2. The soft magnetic stainless steel profile according to claim 1, characterized in that: The content of the element Cr is 15.5 to 16.5% by weight.

3. The soft magnetic stainless steel profile according to claim 1, characterized in that: The content of the element Nb is 0.05 to 0.20 wt %.

4. The soft magnetic stainless steel profile according to claim 1, characterized in that: The content of the element Y is 0.015 to 0.05 wt %.

5. The soft magnetic stainless steel profile according to claim 1, characterized in that: Based on the total weight of the soft magnetic stainless steel, the elements that will serve as the inevitable impurities are: The content of C is controlled below 0.015 wt %; and / or The content of N is controlled to be below 0.005 wt %; and / or The content of O is controlled to be below 0.002 wt %; and / or The content of S is controlled to be below 0.005 wt %; and / or The P content is controlled to be less than 0.005 wt %.

6. The soft magnetic stainless steel profile according to claim 5, characterized in that: The content of the element C as the unavoidable impurity is controlled to be 0.010 wt % or less based on the total weight of the soft magnetic stainless steel.

7. The soft magnetic stainless steel profile according to claim 5, characterized in that: The content of the element N as the unavoidable impurity is controlled to be 0.003 wt % or less based on the total weight of the soft magnetic stainless steel.

8. The soft magnetic stainless steel profile according to claim 5, characterized in that: The content of the element O as the unavoidable impurity is controlled to be 0.0015 wt % or less based on the total weight of the soft magnetic stainless steel.

9. The soft magnetic stainless steel profile according to claim 5, characterized in that: The content of the element S as the unavoidable impurity is controlled to be 0.003 wt % or less based on the total weight of the soft magnetic stainless steel.

10. The soft magnetic stainless steel profile according to claim 5, characterized in that: The content of the element P as the unavoidable impurity is controlled to be 0.003 wt % or less based on the total weight of the soft magnetic stainless steel.

11. The soft magnetic stainless steel profile according to any one of claims 1 to 10, characterized in that: The soft magnetic stainless steel profile is a wire.

12. A product prepared from the soft magnetic stainless steel profile according to any one of claims 1 to 11.

13. The article of manufacture of claim 12, selected from the group consisting of a brake, a relay, and a solenoid valve.

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