Ferritic stainless steel having high-temperature strength and good workability and method for producing the same

Abstract

The application discloses a ferrite stainless steel with high temperature strength and good processability and a preparation method thereof. The preparation method of the ferrite stainless steel with high temperature strength and good processability comprises smelting-casting-grinding-hot rolling-first annealing-cold rolling-second annealing-pickling, wherein the chemical components of the ferrite stainless steel with high temperature strength and good processability are controlled as follows in percentage by mass: C: 0.008-0.015%, Si: 0.30-0.55%, Mn: 0.30-0.55%, P: less than or equal to 0.035%, S: less than or equal to 0.002%, Cr: 17.80-18.20%, Ti: greater than or equal to 4(C+N)+0.20, Ni: 0.15-0.25%, Mo: less than or equal to 0.03%, Nb: less than or equal to 0.01%, N: 0.007-0.013%, Cu: less than or equal to 0.10%, Al: 0.03-0.05%, and the balance is Fe and inevitable impurities. The ferrite stainless steel with high temperature strength and good processability prepared by the above method has effectively improved the yield strength and tensile strength at normal temperature and 320 DEG C, and has low manufacturing cost.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and particularly relates to a ferritic stainless steel with good high-temperature strength and workability and its preparation method. Background Technology

[0002] Ferritic stainless steel refers to stainless steel with a chromium content of 11-30%, a body-centered cubic crystal structure, and a predominantly ferritic microstructure in its service state. Ferritic stainless steel can be classified into three categories based on chromium content: low chromium (11-15%), medium chromium (16-20%), and high chromium (21-30%). Ferritic stainless steel contains little or no nickel, making it a resource-saving material, perfectly suited to my country's nickel resource scarcity. Ferritic stainless steel is characterized by low cost, low coefficient of thermal expansion, and insensitivity to stress corrosion, making it ideal for the heat exchanger industry. Stainless steel finned tubes have better heat exchange efficiency than plain tubes, hence their widespread use in heat exchangers. However, currently, conventionally produced 439 stainless steel has low high-temperature yield strength, coarse grains, or low elongation under increased high-temperature strength conditions, only meeting the requirements for automotive exhaust pipes or heat exchange tubes at room temperature, and not the requirements for higher-temperature finned tubes.

[0003] Chinese patent publication CN110669988A discloses a ferritic stainless steel for nuclear power heat exchangers and its preparation method. The method is characterized by extremely low carbon content, the addition of niobium or molybdenum, and a relatively high chromium content, achieving a yield strength ≥150 MPa at 300℃. However, this method involves the addition of niobium and molybdenum, resulting in high costs; furthermore, it only addresses the yield strength at 300℃, which cannot meet the performance requirements of finned tubes under higher temperature conditions.

[0004] Chinese patent publication CN115612918A discloses a method for preparing ferritic stainless steel with high-temperature performance. The method is characterized by improving high-temperature strength and oxidation resistance through the addition of large amounts of elements such as niobium, molybdenum, copper, and tin. However, this method involves the addition of large amounts of precious metals, resulting in high costs, and the high copper and nickel content leads to poor resistance to stress corrosion.

[0005] Chinese patent publication CN115287539A discloses a stainless steel sheet for automotive exhaust systems with good high-temperature strength and its preparation method. This method improves high-temperature strength and oxidation resistance by adding large amounts of elements such as chromium, silicon, niobium, molybdenum, and aluminum. However, this method requires the addition of large amounts of precious metals, resulting in high costs.

[0006] Therefore, given the aforementioned characteristics of high production cost, poor stress resistance, and poor corrosion resistance, there is a need to provide a ferritic stainless steel with good high-temperature strength and workability, as well as its preparation method, to solve the above-mentioned technical problems. Summary of the Invention

[0007] To address some or all of the technical problems existing in the prior art, the present invention provides a ferritic stainless steel with good high-temperature strength and workability, and a method for preparing the same.

[0008] The preparation method of the high-temperature strength and workable ferritic stainless steel of the present invention includes: smelting-continuous casting-grinding-hot rolling-first annealing-cold rolling-second annealing-pickling, wherein the chemical composition of the high-temperature strength and workable ferritic stainless steel is controlled by mass percentage as follows: C: 0.008%~0.015%, Si: 0.30%~0.55%, Mn: 0.30%~0.55%, P≤0.035%, S≤0.002%, Cr: 17.80%~18.20%, Ti≥4(C+N)+0.20, Ni: 0.15%~0.25%, Mo≤0.03%, Nb≤0.01%, N: 0.007%~0.013%, Cu≤0.10%, Al: 0.03%~0.05%, with the balance being Fe and unavoidable impurities;

[0009] Smelting: Smelting stainless steel according to its chemical composition and mass percentage to produce ferritic stainless steel molten steel;

[0010] Continuous casting: Molten steel is prepared into a 200mm thick continuous casting slab with a ladle temperature of 1545℃~1555℃;

[0011] Grinding: The continuously cast slab is hot-ground at a temperature of 350℃~550℃.

[0012] Hot rolling: Heating the continuously cast slab to a temperature T 铸 =1180℃~1200℃, the continuous casting plate is heated for 200min~220min, and then hot coils are obtained through rough rolling, finish rolling and coiling. The rough rolling temperature T 粗 =1040℃~1060℃, final rolling temperature T 终 =830℃~850℃, winding temperature T 卷 =630℃~650℃, winding thickness is 6mm;

[0013] First annealing: The hot coil is annealed continuously at an annealing temperature T. 热退 = (870 + 2Cr + 60Ti + 30Al)℃, hold for 1.2 min / mm;

[0014] Cold rolling: cold rolling deformation rate 70%~80%, final cold-rolled plate thickness 1.4mm~1.8mm;

[0015] Second annealing: Anneal the cold plate at temperature T. 冷退 = (845+2Cr+60Ti+30Al)℃, hold for 1min / mm.

[0016] Furthermore, the above-mentioned method for preparing ferritic stainless steel with good high-temperature strength and workability also includes a pickling step of the steel plate after the second annealing.

[0017] In a second aspect of the invention, a ferritic stainless steel with high-temperature strength and good workability is provided;

[0018] The chemical composition of the ferritic stainless steel with high temperature strength and good workability is controlled by mass percentage as follows: C: 0.008%~0.015%, Si: 0.30%~0.55%, Mn: 0.30%~0.55%, P≤0.035%, S≤0.002%, Cr: 17.80%~18.20%, Ti≥4(C+N)+0.20%, Ni: 0.15%~0.25%, Mo≤0.03%, Nb≤0.01%, N: 0.007%~0.013%, Cu≤0.10%, Al: 0.03%~0.05%, with the balance being Fe and unavoidable impurities.

[0019] Preferably, in the above-mentioned ferritic stainless steel with high temperature strength and good workability, C: 0.008%~0.014%, N: 0.008%~0.012%, Si: 0.38%~0.45%, Mn: 0.40%~0.50%, and P: 0.018%~0.025%.

[0020] Preferably, in the above-mentioned ferritic stainless steel with high temperature strength and good workability, Ti: 0.33~0.40, N: 0.008~0.012, and Al is (0.10~0.12)*Ti.

[0021] Furthermore, in the above-mentioned ferritic stainless steel with good high-temperature strength and workability, the average grain size G is: grade 7.0 to 8.0. The contribution of C, N, Si, Mn, P and average grain size G to the room temperature yield strength of cold plate is 260 + 40Si + 10Mn + 80(C + N) + 60P + 15(G - 6).

[0022] Furthermore, among the aforementioned ferritic stainless steels with good high-temperature strength and workability, the yield strength at room temperature is 290 MPa to 310 MPa, the tensile strength is 450 MPa to 480 MPa, and the elongation is 33% to 38%.

[0023] The yield strength at 320℃ is 210 MPa to 245 MPa, and the tensile strength is 370 MPa to 390 MPa.

[0024] The ferritic stainless steel with good high-temperature strength and workability and its preparation method of the present invention have the following advantages and

[0025] Beneficial effects:

[0026] This invention effectively improves the strength of ferritic stainless steel, effectively reduces internal cracks in the casting billet, and improves the yield strength and tensile strength at room temperature and 320℃. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for further understanding of the embodiments of the present invention and constitute a part of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0028] Figure 1 The microstructure of the cold plate in Example 1 of the embodiments;

[0029] Figure 2 The microstructure of the cold plate is shown as a comparative example in this embodiment. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] The preparation method of the high-temperature strength and workable ferritic stainless steel of the present invention includes: smelting-continuous casting-grinding-hot rolling-first annealing-cold rolling-second annealing-pickling, wherein the chemical composition of the high-temperature strength and workable ferritic stainless steel is controlled by mass percentage as follows: C: 0.008%~0.015%, Si: 0.30%~0.55%, Mn: 0.30%~0.55%, P≤0.035%, S≤0.002%, Cr: 17.80%~18.20%, Ti≥4(C+N)+0.20, Ni: 0.15%~0.25%, Mo≤0.03%, Nb≤0.01%, N: 0.007%~0.013%, Cu≤0.10%, Al: 0.03%~0.05%, with the balance being Fe and unavoidable impurities;

[0032] Smelting: Stainless steel is smelted according to its chemical composition and mass percentage to produce ferritic stainless steel. During the smelting process, the ferrite potential is controlled by adjusting the chemical composition of the ferritic stainless steel. The ferrite potential FP = 5.26(0.71-Ni).当量 / Cr 当量 This allows the ferrite potential to be controlled at 3.40–3.50, thereby reducing internal cracks in the cast billet.

[0033] Among them, Ni 当量 =Ni+0.5Mn+30(C+N)+0.3Cu, Cr 当量 =Cr + 1.5Si + 1.5Ti + 5.5Al;

[0034] Continuous casting: Molten steel is prepared into a 200mm thick continuous casting slab with a ladle temperature of 1545℃~1555℃;

[0035] Grinding: The continuously cast slab is hot-ground at a temperature of 350℃~550℃.

[0036] Hot rolling: Heating the continuously cast slab to a temperature T 铸 =1180℃~1200℃, the continuous casting plate is heated for 200min~220min, and then hot coils are obtained through rough rolling, finish rolling and coiling. The rough rolling temperature T 粗 =1040℃~1060℃, final rolling temperature T 终 =830℃~850℃, winding temperature T 卷 =630℃~650℃, winding thickness is 6mm;

[0037] First annealing: The hot coil is annealed continuously at an annealing temperature T. 热退 = (870 + 2Cr + 60Ti + 30Al)℃, hold for 1.2 min / mm;

[0038] Cold rolling: cold rolling deformation rate 70%~80%, final cold-rolled plate thickness 1.4mm~1.8mm;

[0039] Second annealing: Anneal the cold plate at temperature T. 冷退 = (845+2Cr+60Ti+30Al)℃, hold for 1min / mm.

[0040] Furthermore, the method for preparing ferritic stainless steel with high-temperature strength and good workability of the present invention also includes a pickling step of the steel plate after the second annealing.

[0041] In a second aspect of the invention, a ferritic stainless steel with high-temperature strength and good workability is provided, wherein the chemical composition of the ferritic stainless steel is controlled by mass percentage as follows: C: 0.008%–0.015%, Si: 0.30%–0.55%, Mn: 0.30%–0.55%, P≤0.035%, S≤0.002%, Cr: 17.80%–18.20%, Ti≥4(C+N)+0.20, Ni: 0.15%–0.25%, Mo≤0.03%, Nb≤0.01%, N: 0.007%–0.013%, Cu≤0.10%, Al: 0.03%–0.05%, with the balance being Fe and unavoidable impurities.

[0042] Preferably, in the ferritic stainless steel of the present invention, which has good high-temperature strength and workability, C: 0.008%~0.014%, N: 0.008%~0.012%, Si: 0.38%~0.45%, Mn: 0.40%~0.50%, and P: 0.018%~0.025%, thereby effectively improving the strength of the ferritic stainless steel. The contribution of C, N, Si, Mn, P and average grain size G (average grain size) to the room temperature yield strength of the cold plate is 260+40Si+10Mn+80(C+N)+60P+15(G-6).

[0043] Preferably, in the above-mentioned ferritic stainless steel with high temperature strength and good workability, Ti: 0.33~0.40, N: 0.008~0.012. Since too little Al content will affect the stability of Ti content, and too much Al content will increase the brittle transition temperature of the material, Al is (0.10~0.12)*Ti.

[0044] Furthermore, in the aforementioned ferritic stainless steels with good high-temperature strength and workability, the average grain size G is grade 7.0 to 8.0.

[0045] Furthermore, among the aforementioned ferritic stainless steels with good high-temperature strength and workability, the yield strength at room temperature is 290 MPa to 310 MPa, the tensile strength is 450 MPa to 480 MPa, and the elongation is 33% to 38%.

[0046] The yield strength at 320℃ is 210 MPa to 245 MPa, and the tensile strength is 370 MPa to 390 MPa.

[0047] Example 1:

[0048] Smelting: Smelt stainless steel according to the chemical composition in Table 1 by mass percentage to produce ferritic stainless steel molten steel;

[0049] Continuous casting: Molten steel is prepared into a 200mm thick continuous casting slab with a ladle temperature of 1545℃~1555℃;

[0050] Grinding: The continuously cast slab is hot-ground at a temperature of 350℃~550℃.

[0051] Hot rolling: The continuously cast slab is heated to 1180℃~1200℃ for 200min~220min, then rough rolled at 1040℃~1060℃, and then finished rolled at 830℃~850℃. After cooling, it is coiled to obtain hot rolled coil at 630℃~650℃.

[0052] First annealing: Annealing temperature T 热退 = (870 + 2Cr + 60Ti + 30Al)℃;

[0053] Cold rolling: cold rolling deformation rate 70%~80%, final cold-rolled plate thickness 1.4mm~1.8mm;

[0054] Second annealing: Annealing temperature T 冷退 = (845 + 2Cr + 60Ti + 30Al)℃, after annealing, pickling is performed.

[0055] Table 1 shows the chemical composition by mass percentage, where 1 to 4 are examples of inventions, and 5 is a comparative example (439 ferritic stainless steel, which is currently widely used in elevators and exhaust systems).

[0056] Table 1 Chemical composition of the invention examples and comparative examples, wt%

[0057]

[0058] Table 2 shows the process parameters, where 1 to 4 are the process parameters for the preparation process of the invention examples, and 5 is the process parameters for the preparation process of the comparative examples.

[0059] Table 2 Process Parameters

[0060]

[0061] Table 3 shows the performance indicators of the examples and comparative examples of this invention. The mechanical properties at room temperature were tested according to GB / T 228.1 "Metallic materials - Tensile testing - Part 1: Test method at room temperature"; the mechanical properties at high temperature were tested according to GB / T 228.2 "Metallic materials - Tensile testing - Part 2: Test method at high temperature"; and the grain size was tested according to GB / T 6394-2017 "Method for determination of average grain size of metals".

[0062] Table 3 Performance Indicators of Cold-rolled Steel Plate

[0063]

[0064] Therefore, compared with the comparative example, the mechanical properties, room temperature yield strength, tensile strength, tensile strength at 320℃ and yield strength of the invention are all improved.

[0065] In summary, compared with the prior art, the ferritic stainless steel with good high-temperature strength and workability and its preparation method of the present invention have the following advantages and beneficial effects:

[0066] This invention effectively improves the strength of ferritic stainless steel, effectively reduces internal cracks in the casting billet, and improves the yield strength and tensile strength at room temperature and 320℃.

[0067] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely 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. Meanwhile, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. In addition, the terms "front," "rear," "left," "right," "upper," and "lower" in this document refer to the placement states shown in the accompanying drawings.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of producing a ferritic stainless steel having high-temperature strength and good workability, characterized by, The preparation method of the high-temperature strength and good processability ferritic stainless steel comprises smelting, continuous casting, dressing, hot rolling, first annealing, cold rolling, second annealing and pickling, wherein the chemical components of the high-temperature strength and good processability ferritic stainless steel are controlled as follows in percentage by mass: C: 0.008% to 0.015%, Si: 0.30% to 0.55%, Mn: 0.30% to 0.55%, P: ≤0.035%, S: ≤0.002%, Cr: 17.80% to 18.20%, Ti: ≥4(C+N)+0.20, Ni: 0.15% to 0.25%, Mo: ≤0.03%, Nb: ≤0.01%, N: 0.007% to 0.013%, Cu: ≤0.10%, Al: 0.03% to 0.05%, and the balance of Fe and inevitable impurities; Smelting: smelting the stainless steel into ferritic stainless steel melt according to the chemical components in percentage by mass; Continuous casting: preparing the melt into a continuous casting slab with a thickness of 200 mm, and the tundish temperature is 1545℃ to 1555℃; Dressing: hot dressing the continuous casting slab, and the dressing temperature is 350℃ to 550℃; Hot rolling: heating continuous casting slab, heating temperature T 铸 = 1180-1200℃, heating time of continuous casting slab is 200-220 min, then hot coil is obtained by rough rolling, finish rolling and coiling, rough rolling temperature T 粗 = 1040-1060℃, finish rolling temperature T 终 = 830-850℃, coiling temperature T 卷 = 630-650℃, coiling thickness is 6 mm; First annealing: continuous annealing of the hot coil, annealing temperature T 热退 = (870 + 2Cr + 60Ti + 30Al) °C, holding time 1.2 min / mm; Cold rolling: the cold rolling deformation rate is 70% to 80%, and the final cold plate thickness is 1.4 mm to 1.8 mm; Second annealing: anneal the cold plate at an annealing temperature T 冷退 = (845 + 2Cr + 60Ti + 30Al) °C for 1 min / mm.

2. The method of producing a ferritic stainless steel excellent in high-temperature strength and workability as claimed in claim 1, characterized by, The method further comprises the step of pickling the steel plate after the second annealing is completed.

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