Super ferritic stainless steel with good processability as well as preparation method and application of super ferritic stainless steel

Abstract

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

Description

Technical Field

[0001] The present application relates to the field of alloy technology, and in particular to a super ferrite stainless steel with good processing performance, a preparation method and an application thereof. Background Art

[0002] Super ferritic stainless steel refers to a type of alloy with a Cr content of 25% to 30%, C+N ≤ 150ppm, pitting resistance equivalent (PRE) ≥ 35, and a ferrite structure. Compared with chromium-nickel austenitic stainless steel, ferritic stainless steel does not contain nickel or contains only a small amount of nickel, so it is a type of nickel-saving stainless steel. Compared with austenitic stainless steel, ferritic stainless steel has high strength and a low tendency to cold work hardening. The thermal conductivity is 130% to 150% of austenitic stainless steel, and the linear expansion coefficient is only 60% to 70% of austenitic stainless steel. Due to its high Cr and Mo content, super ferritic stainless steel has excellent resistance to pitting corrosion, crevice corrosion and stress corrosion in chloride media. It is mainly used as a low-cost heat exchange material in corrosive environments. Vigorously promoting ferritic stainless steel can greatly save my country's nickel resources.

[0003] On the one hand, since high chromium and high molybdenum ferritic stainless steel contains high Cr and high Mo, it has excellent corrosion resistance but also brings the problem of σ phase precipitation brittleness. The σ phase precipitation brittleness temperature range is about 750-960°C, which deteriorates the plastic toughness and processing performance of super ferritic stainless steel, restricting the application of super ferritic stainless steel. Especially in fuel cell system components, these components are often press-processed by steel plates, so the formability of cold-rolled steel plates as substrates is required. On the other hand, since the operating temperature of fuel cells is 600-900°C, it is necessary to increase the amount of alloys such as Cr, Mo, and Nb to improve the medium and high temperature strength. However, if the added elements increase, the machinability of the substrate steel plate decreases, so pressure forming is often not possible for components with complex shapes. In order to improve the workability of super ferritic stainless steel sheets, it is effective to adopt a larger cold rolling reduction rate. However, due to the large difference in thickness specifications of fuel cell system components (0.1 to 10 mm), the thickness of the substrate during cold rolling is limited to a certain extent in the current manufacturing process, and there is a problem that the cold rolling reduction rate cannot be fully ensured. Therefore, how to improve the workability of super ferritic stainless steel is a technical problem that needs to be solved urgently. Summary of the invention

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

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

[0006] Optionally, the chemical composition satisfies the following relationship:

[0007] [Cr]+3.3×[Mo]≥35%

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

[0009] Optionally, the chemical composition satisfies the following relationship:

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

[0011] Wherein, [%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, and [%N] represents the value before the mass fraction % of N.

[0012] Optionally, the chemical composition satisfies 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 composition satisfies 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 metallographic structure of the super ferrite stainless steel is ≤3%.

[0019] Optionally, the hot working window of the super ferrite stainless steel is 500°C to 750°C.

[0020] In a second aspect, the present application provides a method for preparing the super ferrite stainless steel according to any one embodiment of the first aspect, the method comprising:

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

[0022] Casting and crystallizing the alloyed steel liquid to obtain an alloy ingot with the chemical composition;

[0023] The alloy ingot is sequentially heated, forged and tempered multiple times to obtain a slab;

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

[0025] The hot-rolled strip is subjected to blanking, intermediate heat treatment, multiple cold rolling and solution treatment to obtain a strip;

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

[0027] Optionally, the multiple cold rolling and the annealing treatment satisfy the following relationship:

[0028] When the total reduction of the multiple cold rolling passes is ≥70%, the parameters of the annealing treatment are as follows: the heating temperature is 900°C to 1000°C, and the holding time is 30min to 45min;

[0029] When the total reduction of the multiple cold rolling passes is less than 70%, the parameters of the annealing treatment are as follows: the heating temperature is 1050° C. to 1100° C., and the holding time is 45 min to 60 min.

[0030] In a third aspect, the present application provides a fuel cell interconnection plate, wherein the fuel cell interconnection plate is made of the super ferrite stainless steel described in any one embodiment of the first aspect, and the fuel cell interconnection plate satisfies at least one of the following properties:

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

[0032] The elongation A is 60% to 90%.

[0033] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0034] The present application provides a super ferritic stainless steel with good processing performance, which includes the following chemical components by mass fraction: Cr: 23% to 30%, Mo: 4% to 6%, Zr: 0.4% to 1%, B: 0.015% to 0.4%, Nb: 1.0% to 4%, Ti: 0.05% to 3%, Ni: 0.2% to 1%, Ru: 0.05% to 1%, C<0.008%, TO≤0.002%, N≤0.001%, Si: 0.15% to 0.3%, Mn: 0.1% to 0.8%, Al: 0.15% to 0.4% and Fe. Through the reasonable proportion of chemical components, the C and N components that affect the processing performance of the interconnection plate are controlled to be extremely low during the smelting process, and Nb and Ti are used to stabilize the residual C and N. It is also proposed to suppress 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 element enrichment concentration reaches the critical value of precipitation, the B2A structure Laves phase, namely (Fe,Cr)2(Mo,Nb), will begin to precipitate, which is brittle, reduces the plasticity of the alloy, and deteriorates the alloy processing performance. B is concentrated at the grain boundary, improving the grain boundary bonding force. The appropriate addition can improve the brittleness of the Laves phase. B dissolved in the alloy can reduce the bonding energy of the Laves phase, reduce the stacking fault energy, facilitate the initiation of twin deformation, and improve toughness; Zr can improve the room temperature plasticity of the Laves intermetallic compound and the medium-temperature plasticity of the alloy. The combined effect of B and Zr can improve the comprehensive performance of the alloy at 600℃~900℃ and improve the processing performance. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0037] Figure 1 A schematic flow chart of a method for preparing super ferritic stainless steel provided in an embodiment of the present application. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0039] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have 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., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0040] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used 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 article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one-to-one with the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

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

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

[0043] The alloying elements added in this application have the following functions:

[0044] Cr: A basic element to ensure the oxidation resistance and thermal expansion performance of the present invention. If the content is less than 23%, the oxidation resistance of the present invention cannot be achieved, and if the content is more than 30%, the thermal expansion performance cannot be satisfied. For example, the Cr content can be 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0045] Ni: Ni can reduce 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, Nb: The addition amount of stabilizing elements Ti and Nb must be strictly controlled. If the content of Ti and Nb is too low to combine with C and N elements, high temperature brittleness cannot be eliminated, but too high an addition amount will deteriorate the plasticity and toughness of stainless steel. Exemplarily, the content of Nb can be 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc. The content of Ti can be 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. The content of C can be 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, etc. The content of N can be 0.0005%, 0.0006%, 0.0007%, 0.0008%, 0.00009%, 0.001%, etc.

[0047] Ru: σ phase is a size factor compound with AB or AxBy configuration and body-centered tetragonal structure. A is Fe, and B is one or more of Cr, Mo, and Nb. The σ phase is non-magnetic and has a high hardness. The Rockwell hardness (HRC) can reach 68HRC. The precipitation process will be accompanied by a "volume effect", and the plasticity of the steel will decrease. The addition of Ru will change and increase the mismatch between the ferrite matrix and the new phase, increase the nucleation barrier of the brittle phase, and inhibit the precipitation of the σ brittle phase during long-term aging, thereby improving the processing properties of the material. Exemplarily, the Ru content can be 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, etc.

[0048] Mo: A solid solution strengthening element that can improve alloy strength and corrosion resistance; however, the atomic number is relatively high, which will increase the alloy density and increase the cost. In addition, the addition of Mo element has the effect of significantly reducing the thermal expansion coefficient of nickel-based alloys. If the content is too low, the strength improvement and corrosion resistance effect at medium temperature are not significant. If the content is too high, it is easy to cause the rapid precipitation of brittle phases. The optimal content is controlled at 4% to 6%. Exemplarily, the Mo content can be 4%, 4.5%, 5%, 5.5%, 6%, etc.

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

[0050] B: B is concentrated at the grain boundary to improve the grain boundary bonding strength. Adding an appropriate amount can improve the brittleness of Laves intermetallic compounds. The combined effect of B and Zr can improve the comprehensive performance of the alloy at 600℃ to 900℃. For example, the content of B can be 0.015%, 0.02%, 0.05%, 0.1%, 0.3%, 0.4%, etc.

[0051] Si: deoxidizer, can improve the oxidation resistance and high temperature strength of the alloy. Excessive addition will form SiO2 on the surface of the alloy during the oxidation process, affecting the conductivity. Exemplarily, the Si content can be 0.15%, 0.18%, 0.2%, 0.24%, 0.28%, 0.3%, etc.

[0052] Mn: deoxidizer, can improve the oxidation resistance and high temperature strength of the alloy. Excessive addition will increase the thermal expansion coefficient of the alloy. Exemplarily, the content of Mn 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 the alloy. It can also reduce the density of the alloy, achieving the advantages of lightweight and low cost. Excessive addition affects the tensile and welding properties. 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 is the total oxygen content.

[0055] Fe is a matrix element. The specific content / content range of Fe can be obtained through the upper and lower limit formulas of the components, that is, the sum of the percentages of the contents of each component in a composition should be equal to 100%, and the content ranges of several components should meet the following conditions: the upper limit value of a component + the lower limit values ​​of other components ≤ 100; the lower limit value of a component + the upper limit values ​​of other components ≥ 100.

[0056] In some embodiments, the chemical composition satisfies the following relationship:

[0057] [Cr]+3.3×[Mo]≥35%

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

[0059] In some embodiments, the chemical composition satisfies the following relationship:

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

[0061] Wherein, [%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, and [%N] represents the value before the mass fraction % of N.

[0062] The present application controls the C and N components that affect the processing performance of the interconnection plate to extremely low levels during the smelting process through a reasonable ratio of chemical components, and uses Nb and Ti to stabilize the residual C and N. It is defined that ([%Ti]+[%Nb])≥0.32+4×([%C]+[%N]) and 0.32+4×([%C]+[%N])≤0.6, thereby ensuring that Ti and Nb can combine with C and N elements, thereby eliminating high-temperature brittleness and avoiding deterioration of the plasticity and toughness of stainless steel.

[0063] In some embodiments, the chemical composition satisfies 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 medium-temperature oxidation conditions, due to the outward diffusion of Cr to form vacancies, the movement of Mo and Nb phase vacancies will form a B2A structure Laves phase, namely (Fe,Cr)2(Mo,Nb), which begins to precipitate when the element enrichment concentration reaches the critical value of precipitation. It is brittle, reduces the plasticity of the alloy, and deteriorates the processing performance of the alloy. The addition of Ru will change and increase the mismatch between the ferrite matrix and the new phase, increase the nucleation barrier of the brittle phase, and inhibit the precipitation of the σ brittle phase during long-term aging, thereby improving the processing performance of the material. It is limited to 0.001≤[Ru] / ([Cr]+3.2[Mo]+[Nb])≤0.04, so that the precipitation of the σ brittle phase can be better inhibited. Exemplarily, 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 composition satisfies 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] The limit of 0.05≤([Zr]+1.1[B]) / ([Mo]+[Nb])≤0.2 can further improve the brittle effect of the Laves intermetallic compound. 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 metallographic structure of the super ferrite stainless steel is ≤3%.

[0072] σ phase is a hard and brittle Fe-Cr intermetallic compound, and its precipitation will cause the plasticity and toughness of stainless steel to be significantly reduced, that is, σ phase brittleness will be generated. In super ferritic stainless steel, the volume fraction of σ brittle phase needs to be strictly controlled to ensure the comprehensive performance of the material. For example, the volume fraction of σ brittle phase in the metallographic structure 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] The present application improves the processing performance of the material by designing reasonable alloy element addition and ratio, and reasonable rolling process parameter control. The alloy has a wide hot working window, few surface cracks during alloy processing, good plasticity, and high yield rate. Exemplarily, the hot working window of the super ferritic stainless steel can be 500℃, 520℃, 550℃, 600℃, 650℃, 700℃, 750℃, etc.

[0075] In summary, in the present application, through 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 melting process, and 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, since Cr diffuses outwards to form vacancies, the movement of Mo and Nb phase vacancies will form the B2A structure Laves phase, i.e., (Fe,Cr)2(Mo,Nb), which begins to precipitate when the enrichment concentration of elements reaches the precipitation critical value. 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 binding bond energy 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 action 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 ferrite stainless steel provided by an embodiment of the present application.

[0077] Please refer to Figure 1 , the present application provides a preparation method of the super ferrite 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 relationship between the time of the vacuum refining and the pressure of the vacuum refining is as follows:

[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] Wherein, 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 to promote the escape of gases (such as hydrogen, oxygen, etc.) in the molten steel, and also helps with the rapid melting and uniform mixing of the raw materials; in the middle stage of refining (0.2T < t < 0.6T), limiting P to 0.1 Pa to 0.5 Pa helps to 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 conducive 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 to maintain the stability of the molten steel, preventing the splashing or spattering of the molten steel caused by too low pressure. At the same time, it also helps to 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, i.e., when T.O ≤ 20 ppm in the alloy.

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

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

[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 the surface finishing is: using a polishing wheel with a particle size of 500-1000 meshes for rough polishing, and then using a polishing wheel with a particle size of 3000-4000 meshes for fine polishing.

[0096] In some embodiments, the multiple cold rolling passes and the annealing treatment satisfy the following relationship:

[0097] When the total reduction of the multiple cold rolling passes is ≥70%, the parameters of the annealing treatment are as follows: the heating temperature is 900°C to 1000°C, and the holding time is 30min to 45min;

[0098] When the total reduction of the multiple cold rolling passes is less than 70%, the parameters of the annealing treatment are as follows: the heating temperature is 1050° C. to 1100° C., and the holding time is 45 min to 60 min.

[0099] In ferritic stainless steel, the brittle phase 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 a high hardness, with a Rockwell hardness (HRC) of up to 68HRC. The precipitation process is accompanied by a "volume effect", and the plasticity of the steel will decrease. The increase in cold rolling reduction strengthens the γ fiber texture of the cold-rolled annealed sheet and weakens the α fiber texture, thereby improving the formability of the material. At the same time, as the cold rolling reduction increases, the dislocation density increases, the nucleation points of the σ brittle phase increase, and the amount of brittle phase precipitation is large, which reduces the formability of the material. In order to resolve the two contradictions, the relationship between the cold rolling reduction and the cold rolling annealing temperature and time is controlled. The total reduction of the present invention is higher than 70%, the heating temperature is above 900-1000°C, and the holding time is 30min-45min; the total reduction is lower than 70%, the solution temperature is 1050-1100°C, and the holding time is 45min-60min; a single γ-fiber recrystallization texture is exhibited and the brittle phase σ does not exceed 3%. This strong γ-fiber texture is beneficial to improving the forming performance of ferrite stainless steel. Exemplarily, when the total reduction of the multiple cold rolling passes is ≥70%, the heating temperature of the annealing treatment can be 900°C, 920°C, 940°C, 960°C, 980°C, 1000°C, etc., and the holding time is 30min, 32min, 35min, 40min, 42min, 45min, etc.; when the total reduction of the multiple cold rolling passes is <70%, the heating temperature of the annealing treatment can be 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C, etc., and the holding time is 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 refer 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 one by one here.

[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 ≥ 180 MPa at 900 °C;

[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 conditions recommended by the manufacturer.

[0106] This embodiment provides a preparation method of a super ferritic stainless steel with good workability, which may specifically include the following steps:

[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 blank, and the heating temperature is 1100 °C;

[0109] Step 3, subject the flat slab to multiple hot rolling, annealing, softening, grinding and welding to obtain a hot-rolled strip; the hot rolling temperature is 1150°C. Hot rolling includes: a first hot rolling, a second hot rolling and a third hot rolling. The first hot rolling deformation is 50%, the second hot rolling deformation is 60%, and the third hot rolling deformation is 70%. The final rolling temperature is 900°C. After rolling, solid solution is carried out at 1100°C for 2 hours and water cooled to room temperature;

[0110] Step 4: subjecting the hot-rolled strip to blanking, intermediate heat treatment, cold rolling, intermediate grinding, trimming and solution treatment to obtain a strip. The cold rolling includes: a first cold rolling, a second cold rolling and a third cold rolling;

[0111] Step 5, surface finishing, cleaning and plate shape correction of the strip, the specific process of the surface finishing is: using a polishing wheel with a particle size of 500 mesh for rough polishing, and then using a polishing wheel with a particle size of 4000 mesh for fine polishing.

[0112] Step 6: annealing 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 composition 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 of super ferritic stainless steel (wt, %), the balance is 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 of super ferritic stainless steel

[0118]

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

[0120] Table 4 Hot working window temperature of super ferrite stainless steel of Examples 1 to 5 and Comparative Examples 1 to 6

[0121] serial number Thermal processing 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 interconnection plates prepared from the super ferrite stainless steels of Examples 1 to 5 and Comparative Examples 1 to 6 was measured. The results are shown in Table 5.

[0123] Table 5 High temperature strength of fuel cell interconnection plates of Examples 1 to 5 and Comparative Examples 1 to 6

[0124] serial number Tensile strength Rm at 900℃, MPa 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] As shown in Tables 4 and 5, Comparative Examples 1 to 4 satisfy the relationship between the cold rolling reduction and the cold rolling annealing temperature and time, but 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 the cold rolling reduction and the cold rolling annealing temperature and time is not satisfied. The high temperature mechanical properties of comparative example 1-6 are lower than those of embodiment 1-5, and the hot processing window of comparative example 1-6 is narrower than that of embodiment 1-5, which is not conducive to processing and forming.

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

[0127] In the embodiment of the present application, the processing performance of the material is improved by designing reasonable alloy element addition and ratio, and reasonable rolling process parameter control. The alloy has a wide hot processing window of 500℃~750℃, few surface cracks during alloy processing, good plasticity, and high yield rate.

[0128] In the examples of the present application, the alloy interconnection plate prepared has excellent high temperature strength, wherein the tensile strength Rm at 900°C is above 180 MPa, and the elongation A% is between 60% and 90%, meeting the design and use requirements of the fuel cell interconnection plate.

[0129] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A super ferritic stainless steel with good processing performance, which comprises the following chemical components by mass fraction: Cr: 23% to 30%, Mo: 4% to 6%, Zr: 0.4% to 1%, B: 0.015% to 0.4%, Nb: 1.0% to 4%, Ti: 0.05% to 3%, Ni: 0.2% to 1%, Ru: 0.05% to 1%, C<0.008%, TO≤0.002%, N≤0.001%, Si: 0.15% to 0.3%, Mn: 0.1% to 0.8%, Al: 0.15% to 0.4% and Fe.

2. The super ferrite stainless steel according to claim 1, characterized in that: The chemical composition satisfies the following relationship: [Cr]+3.3×[Mo]≥35% Wherein, [Cr] represents the mass fraction of Cr, and [Mo] represents the mass fraction of Mo.

3. The super ferrite stainless steel according to claim 1, characterized in that: The chemical composition satisfies the following relationship: ([%Ti] + [%Nb]) ≥ 0.32 + 4 × ([%C] + [%N]) and 0.32 + 4 × ([%C] + [%N]) ≤ 0.6 Wherein, [%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, and [%N] represents the value before the mass fraction % of N.

4. The super ferrite stainless steel according to claim 1, characterized in that: The chemical composition satisfies the following relationship: 0.001≤[Ru] / ([Cr]+3.2[Mo]+[Nb])≤0.04 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.

5. The super ferrite stainless steel according to claim 1, characterized in that: The chemical composition satisfies the following relationship: 0.05≤([Zr]+1.1[B]) / ([Mo]+[Nb])≤0.2 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.

6. The super ferrite stainless steel according to claim 1, characterized in that: The volume fraction of the σ brittle phase in the metallographic structure of the super ferrite stainless steel is ≤3%.

7. The super ferrite stainless steel according to claim 1, characterized in that: The hot working window of the super ferrite stainless steel is 500°C to 750°C.

8. A method for preparing the super ferritic stainless steel according to any one of claims 1 to 7, the method comprising: The molten steel is subjected to vacuum refining to obtain alloyed molten steel; Casting and crystallizing the alloyed steel liquid to obtain an alloy ingot with the chemical composition; The alloy ingot is sequentially heated, forged and tempered multiple times to obtain a slab; The slab is subjected to multiple hot rolling, annealing, softening, grinding and welding to obtain a hot-rolled strip; The hot-rolled strip is subjected to blanking, intermediate heat treatment, multiple cold rolling and solution treatment to obtain a strip; The strip is subjected to surface finishing, plate shape correction and annealing treatment to obtain the super ferrite stainless steel.

9. The method according to claim 7, characterized in that: The multi-pass cold rolling and the annealing treatment satisfy the following relationship: When the total reduction of the multiple cold rolling passes is ≥70%, the parameters of the annealing treatment are as follows: the heating temperature is 900°C to 1000°C, and the holding time is 30min to 45min; When the total reduction of the multiple cold rolling passes is less than 70%, the parameters of the annealing treatment are as follows: the heating temperature is 1050° C. to 1100° C., and the holding time is 45 min to 60 min.

10. A fuel cell interconnection plate, said fuel cell interconnection plate being made of the super ferrite stainless steel according to any one of claims 1 to 7, and said fuel cell interconnection plate meeting at least one of the following properties: Tensile strength Rm≥180MPa at 900℃; The elongation A is 60% to 90%.

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