Super ferritic stainless steel with good workability, preparation method and application thereof

Abstract

The application provides a super ferritic stainless steel with good processability, a preparation method and application, and belongs to the alloy field.The super ferritic stainless steel comprises the following chemical components: Cr: 23-30%, Mo: 4-6%, Zr: 0.4-1%, B: 0.015-0.4%, Nb: 1.0-4%, Ti: 0.05-3%, Ni: 0.2-1%, Ru: 0.05-1%, C: less than 0.008%, T.O: less than or equal to 0.002%, N: less than or equal to 0.001%, Si: 0.15-0.3%, Mn: 0.1-0.8%, Al: 0.15-0.4% and Fe.Through reasonable matching of the chemical components, the processability of the super ferritic stainless steel is improved.

Description

Technical Field

[0001] This application relates to the field of alloy technology, and in particular to a super ferritic stainless steel with good processing performance, its preparation method, and its application. Background Technology

[0002] Super ferritic stainless steel refers to a class of alloys with a Cr content of 25%–30%, C+N ≤ 150 ppm, pitting resistance equivalent (PRE) ≥ 35, and a ferritic microstructure. Compared to chromium-nickel austenitic stainless steel, ferritic stainless steel contains no nickel or only a small amount of nickel, making it a nickel-saving stainless steel. Compared to austenitic stainless steel, ferritic stainless steel has higher strength and a lower tendency for cold work hardening. Its thermal conductivity is 130%–150% that of austenitic stainless steel, and its coefficient of linear expansion is only 60%–70% of that of austenitic stainless steel. Due to its high Cr and Mo content, super ferritic stainless steel exhibits excellent resistance to chloride media pitting corrosion, crevice corrosion, and stress corrosion. It is mainly used as a low-cost heat exchange material in corrosive environments. Vigorously promoting ferritic stainless steel can greatly conserve my country's nickel resources.

[0003] On the one hand, while high-chromium and high-molybdenum ferritic stainless steels possess excellent corrosion resistance due to their high Cr and Mo content, they also suffer from σ-phase precipitation brittleness, with a precipitation brittleness temperature range of approximately 750–960℃. This deteriorates the ductility and toughness of super ferritic stainless steel, worsens its processing performance, and restricts its application. This is particularly true in fuel cell system components, which are often pressure-processed from steel sheets, thus requiring high formability of the cold-rolled steel sheet used as the base material. On the other hand, since fuel cells operate at temperatures of 600–900℃, it is necessary to increase the amount of alloying elements such as Cr, Mo, and Nb to improve medium- and high-temperature strength. However, increasing the amount of added elements reduces the processability of the base steel sheet, making it often impossible to pressure-form complex-shaped components. To improve the machinability of superferritic stainless steel sheets, a larger cold rolling reduction rate is effective. However, due to the significant differences in thickness specifications (0.1–10 mm) used in fuel cell system components, the current manufacturing process, which limits the base material thickness during cold rolling, presents a problem in ensuring a sufficient cold rolling reduction rate. Therefore, improving the machinability of superferritic stainless steel is an urgent technical problem to be solved. Summary of the Invention

[0004] This application provides a super ferritic stainless steel with good processing performance, its preparation method, and its application, in order to solve the following technical problem: how to improve the processing performance of super ferritic stainless steel.

[0005] In a first aspect, this application provides a super ferritic stainless steel with good processing performance, wherein the super ferritic stainless steel comprises the following chemical composition by mass fraction: Cr: 23%–30%, Mo: 4%–6%, Zr: 0.4%–1%, B: 0.015%–0.4%, Nb: 1.0%–4%, Ti: 0.05%–3%, Ni: 0.2%–1%, Ru: 0.05%–1%, C<0.008%, TO≤0.002%, N≤0.001%, Si: 0.15%–0.3%, Mn: 0.1%–0.8%, Al: 0.15%–0.4%, and Fe.

[0006] Optionally, the chemical components satisfy the following relationship:

[0007] [Cr] + 3.3 × [Mo] ≥ 35%

[0008] In the formula, [Cr] represents the mass fraction of Cr, and [Mo] represents the mass fraction of Mo.

[0009] Optionally, the chemical components satisfy the following relationship:

[0010] (%Ti] + (%Nb) ≥ 0.32 + 4 × (%C] + (%N) and 0.32 + 4 × (%C] + (%N) ≤ 0.6

[0011] In the formula, [%Ti] represents the value preceding the mass fraction % of Ti, [%Nb] represents the value preceding the mass fraction % of Nb, [%C] represents the value preceding the mass fraction % of C, and [%N] represents the value preceding the mass fraction % of N.

[0012] Optionally, the chemical components satisfy the following relationship:

[0013] 0.001≤[Ru] / ([Cr]+3.2[Mo]+[Nb])≤0.04

[0014] In the formula, [Ru] represents the mass fraction of Ru, [Cr] represents the mass fraction of Cr, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

[0015] Optionally, the chemical components satisfy the following relationship:

[0016] 0.05≤([Zr]+1.1[B]) / ([Mo]+[Nb])≤0.2

[0017] In the formula, [Zr] represents the mass fraction of Zr, [B] represents the mass fraction of B, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

[0018] Optionally, the volume fraction of the σ-brittle phase in the microstructure of the superferritic stainless steel is ≤3%.

[0019] Optionally, the hot working window of the super ferritic stainless steel is 500℃~750℃.

[0020] Secondly, this application provides a method for preparing the super ferritic stainless steel according to any embodiment of the first aspect, the method comprising:

[0021] The molten steel is vacuum refined to obtain alloyed molten steel;

[0022] The alloyed steel liquid is poured and crystallized to obtain an alloy ingot with the specified chemical composition;

[0023] The alloy ingot is sequentially heated, forged, and tempered multiple times to obtain a flat billet.

[0024] The flat billet is subjected to multiple hot rolling, annealing and softening, and grinding and welding to obtain a hot-rolled strip billet.

[0025] The hot-rolled strip is subjected to billet preparation, intermediate heat treatment, multi-pass cold rolling and solution treatment to obtain strip material;

[0026] The strip is subjected to surface finishing, shape correction and annealing to obtain the super ferritic stainless steel.

[0027] Optionally, the multi-pass cold rolling and the annealing treatment satisfy the following relationship:

[0028] When the total reduction of the multi-pass cold rolling is ≥70%, the parameters of the annealing treatment are as follows: heating temperature is 900℃~1000℃, and holding time is 30min~45min;

[0029] When the total reduction of the multi-pass cold rolling is less than 70%, the parameters of the annealing treatment are as follows: heating temperature is 1050℃~1100℃, and holding time is 45min~60min.

[0030] Thirdly, this application provides a fuel cell interconnect plate, which is made of the super ferritic stainless steel described in any embodiment of the first aspect, and the fuel cell interconnect plate satisfies at least one of the following properties:

[0031] Tensile strength Rm at 900℃ ≥ 180MPa;

[0032] The elongation rate A is 60%–90%.

[0033] The technical solutions provided in this application have the following advantages compared with the prior art:

[0034] This application provides a super ferritic stainless steel with excellent processing performance. By mass fraction, the super ferritic stainless steel comprises the following chemical composition: Cr: 23%–30%, Mo: 4%–6%, Zr: 0.4%–1%, B: 0.015%–0.4%, Nb: 1.0%–4%, Ti: 0.05%–3%, Ni: 0.2%–1%, Ru: 0.05%–1%, C < 0.008%, TO ≤ 0.002%, N ≤ 0.001%, Si: 0.15%–0.3%, Mn: 0.1%–0.8%, Al: 0.15%–0.4%, and Fe. Through a reasonable ratio of chemical components, the C and N components, which affect the processing performance of interconnect boards, are controlled to extremely low levels during the smelting process. Simultaneously, Nb and Ti are used to stabilize residual C and N. Furthermore, it is proposed to suppress the precipitation of Sigma and Chi phases by adding Ru. Under intermediate-temperature oxidation conditions, Cr diffuses outward to form vacancies. The movement of these vacancies in the Mo and Nb phases leads to the precipitation of the Laves phase (Fe,Cr)₂(Mo,Nb) with a B₂A structure, which precipitates when the element concentration reaches a critical precipitation value. This phase is brittle, reducing the alloy's plasticity and deteriorating its processing performance. Boron (B) segregates at grain boundaries, increasing grain boundary bonding strength. Appropriate addition can improve the brittleness of the Laves phase. Boron dissolved in the alloy can lower the bond energy of the Laves phase bonds, reducing stacking fault energy and facilitating twinning deformation, thus improving toughness. Zr can improve both the room-temperature plasticity of the Laves intermetallic compound and the intermediate-temperature plasticity of the alloy. The combined effect of B and Zr can improve the overall performance of the alloy at intermediate temperatures (600℃–900℃) and enhance processing performance. Attached Figure Description

[0035] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic flowchart illustrating a method for preparing a super ferritic stainless steel according to an embodiment of this application. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0040] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple. "Parts representation," such as parts by weight or parts by mass, indicates the proportional relationship between components. In the proportional relationships discussed in this article, parameters described by proportion should be understood as the first term of the proportion in the order of description, while the proportion figure should be understood as the second term. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substances A, B, and C should correspond one-to-one with the proportion figure in the proportion in the order of description, i.e., the mass of substance A : the mass of substance B : the mass of substance C = 1:2:3.

[0041] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0042] This application provides a super ferritic stainless steel with good processing performance. The super ferritic stainless steel comprises the following chemical composition by mass fraction: Cr: 23%~30%, Mo: 4%~6%, Zr: 0.4%~1%, B: 0.015%~0.4%, Nb: 1.0%~4%, Ti: 0.05%~3%, Ni: 0.2%~1%, Ru: 0.05%~1%, C<0.008%, TO≤0.002%, N≤0.001%, Si: 0.15%~0.3%, Mn: 0.1%~0.8%, Al: 0.15%~0.4%, and Fe.

[0043] The alloying elements added in this application serve the following purposes:

[0044] Cr: A fundamental element ensuring the antioxidant and thermal expansion properties of this invention. A Cr content below 23% will not achieve the antioxidant properties required for this invention, while a content above 30% will fail to meet the thermal expansion performance requirements. For example, the Cr content can be 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0045] Ni: Ni can lower the ductile-brittle transition temperature. For example, the Ni content can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, etc.

[0046] Ti and Nb: The amounts of stabilizing elements Ti and Nb must be strictly controlled. If the Ti and Nb content is too low, they are insufficient to bind C and N elements, thus failing to eliminate high-temperature brittleness. However, if the content is too high, it will worsen the ductility and toughness of the stainless steel. For example, the Nb content can be 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc. The Ti content can be 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. The C content can be 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, etc. The N content can be 0.0005%, 0.0006%, 0.0007%, 0.00009%, 0.001%, etc.

[0047] Ru: The σ phase is a size factor compound with an AB or AxBy configuration and a body-centered tetragonal structure. A represents Fe, and B represents one or more of Cr, Mo, and Nb. The σ phase is non-magnetic and has high hardness, reaching a Rockwell hardness (HRC) of 68 HRC. Its precipitation process is accompanied by a "volume effect," which can reduce the plasticity of the steel. The addition of Ru alters and increases the mismatch between the ferrite matrix and the new phase, increasing the nucleation barrier of the brittle phase. During long-term aging, it inhibits the precipitation of the brittle σ phase and improves the processing properties of the material. For example, the Ru content can be 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, etc.

[0048] Mo (Mo) is a solid solution strengthening element that improves alloy strength and corrosion resistance. However, its high atomic number increases alloy density and cost. Furthermore, the addition of Mo significantly reduces the coefficient of thermal expansion of nickel-based alloys. Too low a content results in insignificant strength and corrosion resistance improvements at medium temperatures, while too high a content can lead to rapid precipitation of brittle phases. The optimal content is controlled between 4% and 6%. For example, the Mo content can be 4%, 4.5%, 5%, 5.5%, or 6%.

[0049] Zr: Zr can improve both the room temperature plasticity and the medium temperature plasticity of the alloy. For example, the Zr content can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0050] Boron (B): Boron segregates at grain boundaries, increasing grain boundary bonding strength. Appropriate addition can improve the brittleness of Laves intermetallic compounds. The combined effect of B and Zr can improve the overall properties of the alloy from 600℃ to 900℃. For example, the B content can be 0.015%, 0.02%, 0.05%, 0.1%, 0.3%, 0.4%, etc.

[0051] Si: A deoxidizer that improves the oxidation resistance and high-temperature strength of alloys. Excessive addition can lead to the formation of SiO2 on the alloy surface during oxidation, affecting electrical conductivity. For example, the Si content can be 0.15%, 0.18%, 0.2%, 0.24%, 0.28%, 0.3%, etc.

[0052] Mn: A deoxidizer that improves the oxidation resistance and high-temperature strength of alloys. Excessive addition will increase the coefficient of thermal expansion of the alloy. For example, the Mn content can be 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc.

[0053] Al: A strong deoxidizer that can improve the oxidation resistance and high-temperature strength of alloys. It can also reduce the density of alloys, achieving the advantages of lightweight materials and low cost. Excessive addition, however, affects tensile and weldability. For example, the Al content can be 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc.

[0054] It should be noted that TO represents the total oxygen content.

[0055] Fe is the matrix element. The specific content / range of Fe can be obtained by the formula for the upper and lower limits of the components. That is, the sum of the percentage content of each component in a composition should be equal to 100%. The content range of several components should meet the following conditions: the upper limit of a certain component + the lower limit of other components ≤ 100; the lower limit of a certain component + the upper limit of other components ≥ 100.

[0056] In some embodiments, the chemical components satisfy the following relationship:

[0057] [Cr] + 3.3 × [Mo] ≥ 35%

[0058] In the formula, [Cr] represents the mass fraction of Cr, and [Mo] represents the mass fraction of Mo.

[0059] In some embodiments, the chemical components satisfy the following relationship:

[0060] (%Ti] + (%Nb) ≥ 0.32 + 4 × (%C] + (%N) and 0.32 + 4 × (%C] + (%N) ≤ 0.6

[0061] In the formula, [%Ti] represents the value preceding the mass fraction % of Ti, [%Nb] represents the value preceding the mass fraction % of Nb, [%C] represents the value preceding the mass fraction % of C, and [%N] represents the value preceding the mass fraction % of N.

[0062] This application achieves extremely low levels of C and N components, which affect the processing performance of interconnect boards, during the smelting process through a reasonable ratio of chemical composition. Simultaneously, Nb and Ti are used to stabilize residual C and N. The ratio is limited to ([%Ti]+[%Nb])≥0.32+4×([%C]+[%N]) and 0.32+4×([%C]+[%N])≤0.6, thereby ensuring that Ti and Nb can bind with C and N elements, thus eliminating high-temperature brittleness while avoiding deterioration of the ductility and toughness of the stainless steel.

[0063] In some embodiments, the chemical components satisfy the following relationship:

[0064] 0.001≤[Ru] / ([Cr]+3.2[Mo]+[Nb])≤0.04

[0065] In the formula, [Ru] represents the mass fraction of Ru, [Cr] represents the mass fraction of Cr, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

[0066] Under intermediate-temperature oxidation conditions, due to the outward diffusion of Cr forming vacancies, the movement of vacancies in the Mo and Nb phases leads to the precipitation of the Laves phase (Fe,Cr)2(Mo,Nb) with a B2A structure, which begins to precipitate when the element enrichment concentration reaches the precipitation critical value. This phase is brittle, reduces the alloy's plasticity, and deteriorates its processing performance. The addition of Ru alters and increases the mismatch between the ferrite matrix and the new phase, increasing the nucleation barrier of the brittle phase. During long-term aging, this inhibits the precipitation of the σ-brittle phase and improves the material's processing performance. Limiting the value to 0.001 ≤ [Ru] / ([Cr]+3.2[Mo]+[Nb]) ≤ 0.04 further suppresses the precipitation of the σ-brittle phase. For example, the value of [Ru] / ([Cr]+3.2[Mo]+[Nb]) can be 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, etc.

[0067] In some embodiments, the chemical components satisfy the following relationship:

[0068] 0.05≤([Zr]+1.1[B]) / ([Mo]+[Nb])≤0.2

[0069] In the formula, [Zr] represents the mass fraction of Zr, [B] represents the mass fraction of B, [Mo] represents the mass fraction of Mo, and [Nb] represents the mass fraction of Nb.

[0070] By limiting the embrittlement effect of Laves intermetallic compounds to 0.05 ≤ ([Zr] + 1.1[B]) / ([Mo] + [Nb]) ≤ 0.2, the embrittlement effect can be further improved. For example, the value of ([Zr] + 1.1[B]) / ([Mo] + [Nb]) can be 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, etc.

[0071] In some embodiments, the volume fraction of the σ-brittle phase in the microstructure of the superferritic stainless steel is ≤3%.

[0072] The σ phase is a hard and brittle Fe-Cr intermetallic compound. Its precipitation leads to a significant reduction in the plasticity and toughness of stainless steel, i.e., σ-phase brittleness. In super ferritic stainless steel, the volume fraction of the σ-brittle phase needs to be strictly controlled to ensure the overall performance of the material. For example, the volume fraction of the σ-brittle phase in the microstructure of super ferritic stainless steel can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0073] In some embodiments, the hot working window of the super ferritic stainless steel is 500°C to 750°C.

[0074] This application improves the processing performance of the material by designing reasonable alloying element additions and proportions, and controlling reasonable rolling process parameters. The alloy has a wide hot working window, exhibits fewer surface cracks during processing, good plasticity, and a high yield. For example, the hot working window of this super ferritic stainless steel can be 500℃, 520℃, 550℃, 600℃, 650℃, 700℃, 750℃, etc.

[0075] In summary, in this application, through the reasonable proportioning of chemical components, the C and N components that affect the processing performance of the interconnect board are controlled to an extremely low level during the smelting process. At the same time, Nb and Ti are used to stabilize the residual C and N. And it is proposed to inhibit the precipitation of sigma and chi phases by adding Ru. Under medium-temperature oxidation conditions, due to the outward diffusion of Cr to form vacancies, the movement of Mo and Nb phase vacancies will form. When the enrichment concentration of elements reaches the precipitation critical value, the B2A structure Laves phase, i.e., (Fe,Cr)2(Mo,Nb), begins to precipitate. It is brittle, reduces the plasticity of the alloy, and deteriorates the processing performance of the alloy. B segregates at the grain boundaries, improving the grain boundary bonding force. Appropriate addition can improve the brittleness of the Laves phase. B dissolved in the alloy can reduce the bonding energy of the bonding bonds of the Laves phase, reduce the stacking fault energy, facilitate the initiation of twinning deformation, and improve the toughness; Zr can not only improve the room-temperature plasticity of the Laves intermetallic compound but also improve the medium-temperature plasticity of the alloy. The combined effect of B and Zr can improve the comprehensive medium-temperature performance of the alloy at 600°C to 900°C and improve the processing performance.

[0076] Figure 1 It is a schematic flow chart of a preparation method of a super ferritic stainless steel provided by an embodiment of this application.

[0077] Please refer to Figure 1 , this application provides a preparation method of the super ferritic stainless steel described in any one of the above embodiments, and the method includes:

[0078] S1. Vacuum refine the molten steel to obtain alloyed molten steel;

[0079] In some embodiments, the temperature of the vacuum refining can be 1450°C to 1600°C.

[0080] In some embodiments, the time and pressure of the vacuum refining satisfy the following relationship:

[0081] When t < 0.2T, P is 1 Pa to 5 Pa;

[0082] When 0.2T < t < 0.6T, P is 0.1 Pa to 0.5 Pa;

[0083] When t > 0.6T, P is 1 Pa to 2 Pa;

[0084] Where, t represents the time of the high-temperature refining, P represents the pressure of the high-temperature refining, T represents the total time of the high-temperature refining, and T is 0.5 h to 0.7 h.

[0085] In the initial stage of refining (t < 0.2T), limiting P to 1 Pa to 5 Pa helps promote the escape of gases (such as hydrogen, oxygen, etc.) in the molten steel, and also helps the rapid melting and uniform mixing of raw materials; in the middle stage of refining (0.2T < t < 0.6T), limiting P to 0.1 Pa to 0.5 Pa helps reduce the gas content in the molten steel and further improve the purity of the molten steel. At the same time, the lower pressure is also beneficial to promoting the uniform distribution of alloying elements and the progress of chemical reactions; in the later stage of refining (t > 0.6T), limiting P to 1 Pa to 2 Pa ensures that T.O ≤ 20 ppm and N ≤ 10 ppm in the alloy, and helps maintain the stability of the molten steel, preventing splashing or spattering of the molten steel caused by too low pressure. At the same time, it also helps control the further reaction and precipitation of alloying elements.

[0086] In some embodiments, to ensure the recovery rate of Ru, it is added after deoxidation is completed, that is, when T.O ≤ 20 ppm in the alloy.

[0087] S2. Pour and crystallize the alloyed molten steel to obtain an alloy ingot with the above chemical composition;

[0088] S3. Heat, forge, and perform multi-pass tempering on the alloy ingot in sequence to obtain a flat billet; [[ID=·11]]

[0089] In some embodiments, the heating temperature is 1050 °C to 1200 °C.

[0090] S4. Perform multi-pass hot rolling, annealing softening, and grinding and welding on the flat billet to obtain a hot-rolled strip billet;

[0091] In some embodiments, the hot rolling temperature is 1000 °C to 1150 °C. The hot rolling includes: the first hot rolling, the second hot rolling, and the third hot rolling. The deformation amount of the first hot rolling is 40% to 60%, the deformation amount of the second hot rolling is 40% to 70%, and the deformation amount of the third hot rolling is 50% to 80%. The final rolling temperature is higher than 900 °C. After rolling, it is solution-treated at 1100 °C for 1 h to 2 h and water-cooled to room temperature.

[0092] S5. Perform blooming, intermediate heat treatment, multi-pass cold rolling, and solution treatment on the hot-rolled strip billet to obtain a strip;

[0093] In some embodiments, the multi-pass cold rolling includes: the first cold rolling, the second cold rolling, and the third cold rolling.

[0094] S6. Perform surface finishing, shape correction, and annealing treatment on the strip to obtain the super ferritic stainless steel.

[0095] In some embodiments, the specific process of surface finishing is as follows: rough polishing is performed using a polishing wheel with a grit size of 500-1000 mesh, followed by fine polishing using a polishing wheel with a grit size of 3000-4000 mesh.

[0096] In some embodiments, the multi-pass cold rolling and the annealing treatment satisfy the following relationship:

[0097] When the total reduction of the multi-pass cold rolling is ≥70%, the parameters of the annealing treatment are as follows: heating temperature is 900℃~1000℃, and holding time is 30min~45min;

[0098] When the total reduction of the multi-pass cold rolling is less than 70%, the parameters of the annealing treatment are as follows: heating temperature is 1050℃~1100℃, and holding time is 45min~60min.

[0099] In ferritic stainless steel, the brittle σ phase is a size-factor compound with an AB or AxBy configuration and a body-centered tetragonal structure. The σ phase is non-magnetic and has high hardness, reaching a Rockwell hardness (HRC) of 68 HRC. Its precipitation process is accompanied by a "volume effect," which reduces the steel's plasticity. Increasing the cold rolling reduction enhances the γ-fiber texture and weakens the α-fiber texture in the cold-rolled annealed sheet, improving the material's formability. However, increasing the cold rolling reduction also increases dislocation density, increases the nucleation sites for the brittle σ phase, and leads to a large amount of brittle phase precipitation, reducing the material's formability. To resolve these two contradictions, the relationship between the cold rolling reduction and the cold rolling annealing temperature and time must be controlled. The present invention exhibits a total reduction of over 70%, a heating temperature of 900–1000℃ or higher, and a holding time of 30–45 min; or a total reduction of less than 70%, a solution temperature of 1050–1100℃, and a holding time of 45–60 min; and displays a single γ-fiber recrystallization texture with a brittle phase σ not exceeding 3%. This strong γ-fiber texture is beneficial for improving the formability of ferritic stainless steel. For example, when the total reduction of the multi-pass cold rolling is ≥70%, the heating temperature of the annealing treatment can be 900℃, 920℃, 940℃, 960℃, 980℃, 1000℃, etc., and the holding time can be 30min, 32min, 35min, 40min, 42min, 45min, etc.; when the total reduction of the multi-pass cold rolling is <70%, the heating temperature of the annealing treatment can be 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, etc., and the holding time can be 45min, 48min, 50min, 55min, 60min, etc.

[0100] The product prepared by the preparation method of the ferritic stainless steel is the above-mentioned ferritic stainless steel. The chemical composition and microstructure of the ferritic stainless steel prepared by the preparation method of the ferritic stainless steel can be referred to the above embodiments. Since the preparation method of the ferritic stainless steel adopts some or all of the technical solutions of the embodiments of the ferritic stainless steel, it has at least all the beneficial effects brought by the technical solutions of the embodiments of the ferritic stainless steel, which will not be elaborated here one by one.

[0101] In a third aspect, the present application provides a fuel cell interconnect plate, which is made of the super ferritic stainless steel described in any one of the embodiments in the first aspect, and the fuel cell interconnect plate satisfies at least one of the following performances:

[0102] The tensile strength Rm at 900 °C is ≥180 MPa;

[0103] The elongation A is 60% - 90%.

[0104] The alloy interconnect plate prepared by the present application has both excellent high-temperature strength. The tensile strength Rm at 900 °C is above 180 MPa, and the elongation A% is 60% - 90%, meeting the design and use requirements of the fuel cell interconnect plate.

[0105] The following further elaborates the present application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0106] This embodiment provides a preparation method for a super ferritic stainless steel with good processing performance, which may specifically include the following steps: <00,00220>

[0107] Step 1: Vacuum melt, high-temperature refine, and pour the raw materials proportioned according to the ratio, and obtain an alloy ingot with a set chemical composition after crystallization; wherein, the pressure P of the high-temperature refining and the time t of the high-temperature refining satisfy the following relationship: when t < 0.2T, P varies within the range of 1 Pa to 5 Pa; when 0.2T < t < 0.6T, P varies within the range of 0.1 Pa to 0.5 Pa; when t > 0.6T, P varies within the range of 1 Pa to 2 Pa;

[0108] Step 2: Heat, forge, and perform multi-pass tempering on the alloy ingot to obtain a flat billet, and the heating temperature is 1100 °C; [[ID=,26]]

[0109] Step 3: The flat billet undergoes multiple hot rolling passes, annealing and softening, and grinding and welding to obtain a hot-rolled strip billet; the hot rolling temperature is 1150℃. The hot rolling includes: a first hot rolling pass, a second hot rolling pass, and a third hot rolling pass. The deformation amount in the first hot rolling pass is 50%, in the second hot rolling pass it is 60%, and in the third hot rolling pass it is 70%. The final rolling temperature is 900℃. After rolling, it is solution-treated at 1100℃ for 2 hours and then water-cooled to room temperature.

[0110] Step 4: The hot-rolled strip is subjected to billet preparation, intermediate heat treatment, cold rolling, intermediate grinding, edge trimming, and solution treatment to obtain strip material. Cold rolling includes: a first cold rolling pass, a second cold rolling pass, and a third cold rolling pass;

[0111] Step 5: Perform surface finishing, cleaning, and shape correction on the strip. The specific process of surface finishing is as follows: rough polishing is performed using a 500-mesh polishing wheel, followed by fine polishing using a 4000-mesh polishing wheel.

[0112] Step 6: Anneal the strip to obtain super ferritic stainless steel. The chemical composition of super ferritic stainless steel is shown in Table 1, the relationship between the chemical compositions of super ferritic stainless steel is shown in Table 2, and the relationship between the cold rolling reduction and the cold rolling annealing temperature and time of super ferritic stainless steel is shown in Table 3.

[0113] Table 1. Chemical composition (wt, %) of super ferritic stainless steel, balance being Fe and unavoidable impurities.

[0114]

[0115] Table 2 Relationship between the chemical compositions of super ferritic stainless steel

[0116]

[0117] Table 3. Relationship between cold rolling reduction and cold rolling annealing temperature and time for super ferritic stainless steel.

[0118]

[0119] The hot working window temperatures of the super ferritic stainless steels in Examples 1-5 and Comparative Examples 1-6 were measured, and the results are shown in Table 4.

[0120] Table 4. Hot working window temperatures of superferritic stainless steels in Examples 1-5 and Comparative Examples 1-6

[0121] serial number Heat treatment window temperature, °C Example 1 500～750 Example 2 500～750 Example 3 500～750 Example 4 500～750 Example 5 500～750 Comparative Example 1 550～600 Comparative Example 2 550～600 Comparative Example 3 550～600 Comparative Example 4 550～600 Comparative Example 5 600～650 Comparative Example 6 600～650

[0122] The high-temperature strength of the fuel cell interconnect plates prepared from the super ferritic stainless steels of Examples 1-5 and Comparative Examples 1-6 was measured, and the results are shown in Table 5.

[0123] Table 5. High-temperature strength of fuel cell interconnect plates in Examples 1-5 and Comparative Examples 1-6

[0124] serial number Tensile strength Rm (MPa) at 900℃ Elongation A, % Example 1 180 70 Example 2 180 75 Example 3 185 85 Example 4 185 90 Example 5 190 85 Comparative Example 1 160 55 Comparative Example 2 165 55 Comparative Example 3 168 56 Comparative Example 4 170 58 Comparative Example 5 160 50 Comparative Example 6 155 45

[0125] Tables 4 and 5 show that Comparative Examples 1-4 satisfy the relationship between cold rolling reduction and cold rolling annealing temperature and time. However, Comparative Example 1 does not satisfy [Cr] + 3.3 × [Mo] ≥ 35%, Comparative Example 2 does not satisfy ([%Ti] + [%Nb]) ≥ 0.32 + 4 × ([%C] + [%N]) and 0.32 + 4 × ([%C] + [%N]) ≤ 0.6, Comparative Example 3 does not satisfy 0.001 ≤ [Ru] / ([Cr] + 3.2[Mo] + [Nb]) ≤ 0.04, and Comparative Example 4 does not satisfy 0.05 ≤ ([Zr] + 1.1[B]) / ([Mo] + [Nb]) ≤ 0.2. Comparative Examples 5 and 6 meet the composition requirements. However, the relationship between cold rolling reduction and cold rolling annealing temperature and time is not satisfied. The high-temperature mechanical properties of Comparative Examples 1-6 are lower than those of Examples 1-5, and the hot working window of Comparative Examples 1-6 is narrower than that of Examples 1-5, which is not conducive to processing and forming.

[0126] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0127] In this embodiment, the processing performance of the material is improved by designing reasonable alloy element additions and proportions, and controlling reasonable rolling process parameters. This alloy has a wide hot working window of 500℃ to 750℃, exhibits fewer surface cracks during processing, good plasticity, and a high yield.

[0128] In the embodiments of this application, the alloy interconnect plate obtained has excellent high-temperature strength, with a tensile strength Rm of more than 180 MPa at 900°C and an elongation A% of 60% to 90%, which meets the design and use requirements of fuel cell interconnect plates.

[0129] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A super ferritic stainless steel with good processing properties, wherein the super ferritic stainless steel is composed of the following chemical composition by mass fraction: Cr: 23%–30%, Mo: 4%–6%, Zr: 0.4%–1%, B: 0.015%–0.4%, Nb: 1.0%–4%, Ti: 0.05%–3%, Ni: 0.2%–1%, Ru: 0.05%–1%, C < 0.008%, TO ≤ 0.002%, N ≤ 0.001%, Si: 0.15%–0.3%, Mn: 0.1%–0.8%, Al: 0.15%–0.4%, and Fe and unavoidable impurities, wherein the chemical composition satisfies the following relationship: ([%Ti]+[%Nb])≥0.32+4×([%C]+[%N])and0.32+4×([%C]+[%N])≤0.6; 0.001≤[Ru] / ([Cr]+3.2[Mo]+[Nb])≤0.04; 0.05≤([Zr]+1.1[B]) / ([Mo]+[Nb])≤0.2; In the formula, [%Ti] represents the value before the mass fraction % of Ti, [%Nb] represents the value before the mass fraction % of Nb, [%C] represents the value before the mass fraction % of C, [%N] represents the value before the mass fraction % of N, [Ru] represents the mass fraction of Ru, [Cr] represents the mass fraction of Cr, [Mo] represents the mass fraction of Mo, [Nb] represents the mass fraction of Nb, [Zr] represents the mass fraction of Zr, and [B] represents the mass fraction of B; The volume fraction of σ-brittle phase in the metallographic structure of the super ferritic stainless steel is ≤3%, and the hot working window of the super ferritic stainless steel is 500℃~750℃.

2. The super ferritic stainless steel according to claim 1, characterized in that, The chemical components satisfy the following relationship: [Cr] + 3.3 × [Mo] ≥ 35% In the formula, [Cr] represents the mass fraction of Cr, and [Mo] represents the mass fraction of Mo.

3. A method for preparing the super ferritic stainless steel according to any one of claims 1 to 2, the method comprising: The molten steel is vacuum refined to obtain alloyed molten steel; The alloyed steel liquid is poured and crystallized to obtain an alloy ingot with the specified chemical composition; The alloy ingot is sequentially heated, forged, and tempered multiple times to obtain a flat billet. The flat billet is subjected to multiple hot rolling, annealing and softening, and grinding and welding to obtain a hot-rolled strip billet. The hot-rolled strip is subjected to billet preparation, intermediate heat treatment, multi-pass cold rolling and solution treatment to obtain strip material; The strip is subjected to surface finishing, shape correction and annealing to obtain the super ferritic stainless steel.

4. The method according to claim 3, characterized in that, The multi-pass cold rolling and the annealing treatment satisfy the following relationship: When the total reduction of the multi-pass cold rolling is ≥70%, the parameters of the annealing treatment are as follows: heating temperature is 900℃~1000℃, and holding time is 30min~45min; When the total reduction of the multi-pass cold rolling is less than 70%, the parameters of the annealing treatment are as follows: heating temperature is 1050℃~1100℃, and holding time is 45min~60min.

5. A fuel cell interconnect plate, wherein the fuel cell interconnect plate is made of the super ferritic stainless steel according to any one of claims 1 to 2, and the fuel cell interconnect plate satisfies at least one of the following properties: Tensile strength Rm at 900℃ ≥ 180MPa; The elongation A is 60% to 90%.

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