Ferritic stainless steel with good high-temperature strength and machinability and preparation method thereof

Abstract

The invention discloses ferritic stainless steel with good high-temperature strength and machinability and a preparation method of the ferritic stainless steel. The preparation method of the ferritic stainless steel with the good high-temperature strength and machinability comprises the steps of smelting, continuous casting, coping, hot rolling, primary annealing, cold rolling, secondary annealing and acid pickling. The ferrite stainless steel with the good high-temperature strength and machinability comprises, by mass, 0.008%-0.015% of C, 0.30%-0.55% of Si, 0.30%-0.55% of Mn, smaller than or equal to 0.035% of P, smaller than or equal to 0.002% of S, 17.80%-18.20% of Cr, larger than or equal to 4 (C + N) + 0.20% of Ti, 0.15%-0.25% of Ni, smaller than or equal to 0.03% of Mo, smaller than or equal to 0.01% of Nb, 0.007%-0.013% of N, smaller than or equal to 0.10% of Cu, 0.03%-0.05% of Al and the balance Fe and inevitable impurities. According to the ferritic stainless steel with good high-temperature strength and machinability prepared by the method, the yield strength and tensile strength at normal temperature and 320 DEG C are effectively improved, and the manufacturing cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a ferritic stainless steel with good high temperature strength and processability and a preparation method thereof. Background Art

[0002] Ferritic stainless steel refers to stainless steel with a chromium content of 11-30%, a body-centered cubic crystal structure, and a ferrite structure as the main structure when in use. Ferritic stainless steel can be divided into three categories according to the chromium content: low chromium (11-15%), medium chromium (16-20%), and high chromium (21-30%). Ferritic stainless steel contains no or a small amount of nickel and is a resource-saving material, which is very suitable for the current situation of my country's lack of nickel resources. Ferritic stainless steel has the characteristics of low cost, small thermal expansion coefficient, and insensitivity to stress corrosion. It is very suitable for use in the heat exchanger industry. Stainless steel finned tubes have better heat transfer efficiency than bare tubes, so they are widely used in heat exchangers. However, the 439 stainless steel produced by conventional processes currently has low high-temperature yield strength, coarse grains, or low elongation under conditions of increased high-temperature strength. It can only meet the requirements of automobile exhaust pipes or heat exchange tubes at room temperature, but cannot meet the use requirements of finned tubes at higher temperatures.

[0003] Chinese patent publication number CN110669988A proposes a ferritic stainless steel for nuclear power heat exchangers and its preparation method. The characteristics of this method are: extremely low carbon content, addition of niobium or molybdenum, and high chromium content, and yield strength at 300°C ≥150Mpa. This method adds niobium and molybdenum elements, which is costly; at the same time, it only involves the yield strength at 300°C, which cannot meet the performance requirements of current fin tubes under higher temperature conditions.

[0004] Chinese patent publication number CN115612918A proposes ferritic stainless steel with high temperature performance and its preparation method. The characteristics of this method are: by adding a large amount of niobium, molybdenum, copper, tin and other elements, the high temperature strength and high temperature oxidation resistance are improved. This method adds a large amount of precious metals, the cost is high, and the copper and nickel content is high, and the stress corrosion resistance is poor.

[0005] Chinese patent publication number CN115287539A provides a stainless steel plate for automobile exhaust system with good high temperature strength and a preparation method thereof. The method improves high temperature strength and high temperature oxidation resistance by adding a large amount of chromium, silicon, niobium, molybdenum, aluminum and other elements. The method requires the addition of a large amount of precious metals, which is costly.

[0006] Therefore, in view of the above-mentioned characteristics of high production cost, poor stress resistance and corrosion resistance, it is necessary to provide a ferritic stainless steel with good high temperature strength and processability and a preparation method thereof to solve the above-mentioned technical problems. Summary of the invention

[0007] In order to solve part or all of the technical problems existing in the above-mentioned prior art, the present invention provides a ferritic stainless steel with good high temperature strength and processability and a preparation method thereof.

[0008] The preparation method of the ferritic stainless steel with good high temperature strength and processability of the present invention comprises: smelting-continuous casting-grinding-hot rolling-first annealing-cold rolling-second annealing-pickling, wherein the chemical composition of the ferritic stainless steel with good high temperature strength and processability 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%, and the balance is Fe and unavoidable impurities;

[0009] Smelting: Smelt stainless steel into ferritic stainless steel liquid according to the chemical composition and mass percentage;

[0010] Continuous casting: The molten steel is prepared into a continuous casting slab with a thickness of 200 mm, and the tundish temperature is 1545℃~1555℃;

[0011] Grinding: hot grinding of continuous casting slabs at a temperature of 350°C to 550°C;

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

[0013] First annealing: Continuously anneal the hot coil at annealing temperature T 热退 =(870+2Cr+60Ti+30Al)℃, insulation 1.2min / mm;

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

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

[0016] Furthermore, in the method for preparing the ferritic stainless steel having good high temperature strength and workability, a pickling step of the steel plate is also included after the second annealing is completed.

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

[0018] The chemical composition of the ferritic stainless steel with good high temperature strength and processability is controlled by mass percentage as follows: 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 is Fe and unavoidable impurities.

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

[0020] Preferably, in the above ferritic stainless steel having excellent high temperature strength and workability, Ti is 0.33 to 0.40, N is 0.008 to 0.012, and Al is (0.10 to 0.12)*Ti.

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

[0022] Furthermore, in the above-mentioned ferritic stainless steel with good high temperature strength and workability, the yield strength at room temperature is: 290Mpa~310Mpa, the tensile strength is: 450Mpa~480Mpa, and the elongation is: 33%~38%;

[0023] The yield strength at 320℃ is: 210Mpa~245Mpa, and the tensile strength is: 370Mpa~390Mpa.

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

[0025] Beneficial effects:

[0026] The invention effectively improves the strength of ferritic stainless steel, effectively reduces cracks inside the ingot during ingot casting, and simultaneously improves the yield strength and tensile strength at room temperature and at 320°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings in the following descriptions are only used to further understand the embodiments of the present invention and constitute a part of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

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

[0029] Figure 2 This is the microstructure of the cold plate of the comparative example in the embodiment. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] The preparation method of the ferritic stainless steel with good high temperature strength and processability of the present invention comprises: smelting-continuous casting-grinding-hot rolling-first annealing-cold rolling-second annealing-pickling, wherein the chemical composition of the ferritic stainless steel with good high temperature strength and processability 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%, and the balance is Fe and unavoidable impurities;

[0032] Smelting: Stainless steel is smelted into ferritic stainless steel according to the chemical composition and mass percentage. During the smelting process, the ferrite potential is controlled by controlling the chemical composition of ferritic stainless steel. The ferrite potential FP = 5.26 (0.71-Ni当量 / Cr 当量 ) to control the ferrite potential at 3.40-3.50, and reduce the internal cracks of the ingot by controlling the ferrite potential;

[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: The molten steel is prepared into a continuous casting slab with a thickness of 200 mm, and the tundish temperature is 1545℃~1555℃;

[0035] Grinding: hot grinding of continuous casting slabs at a temperature of 350°C to 550°C;

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

[0037] First annealing: Continuously anneal the hot coil at annealing temperature T 热退 =(870+2Cr+60Ti+30Al)℃, insulation 1.2min / mm;

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

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

[0040] Furthermore, the method for preparing ferritic stainless steel having good high temperature strength and workability of the present invention further comprises a step of pickling the steel plate after the second annealing is completed.

[0041] In a second aspect of the present invention, a ferritic stainless steel having good high temperature strength and processability is provided, wherein the chemical composition of the ferritic stainless steel having good high temperature strength and processability is controlled as follows by mass percentage: 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 remainder is Fe and unavoidable impurities.

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

[0043] Preferably, in the above-mentioned ferritic stainless steel with good high temperature strength and workability, Ti: 0.33-0.40, N: 0.008-0.012, since too little Al content will affect the stability of the 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 above-mentioned ferritic stainless steel having good high temperature strength and workability, the average grain size G is: 7.0 to 8.0.

[0045] Furthermore, in the above-mentioned ferritic stainless steel with good high temperature strength and workability, the yield strength at room temperature is: 290Mpa~310Mpa, the tensile strength is: 450Mpa~480Mpa, and the elongation is: 33%~38%;

[0046] The yield strength at 320℃ is: 210Mpa~245Mpa, and the tensile strength is: 370Mpa~390Mpa.

[0047] Embodiment 1:

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

[0049] Continuous casting: The molten steel is prepared into a continuous casting slab with a thickness of 200 mm, and the tundish temperature is 1545℃~1555℃;

[0050] Grinding: hot grinding of continuous casting slabs at a temperature of 350°C to 550°C;

[0051] Hot rolling: heat the continuous casting slab to 1180℃~1200℃, heat for 200min~220min, then carry out rough rolling at 1040℃~1060℃, after finishing rolling, the final rolling temperature is 830℃~850℃, and after cooling, coiling 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%, the final cold plate thickness 1.4mm ~ 1.8mm;

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

[0055] Table 1 shows the chemical composition in mass percentage, wherein 1 to 4 are invention examples, and 5 is a comparative example (439 ferritic stainless steel currently commonly used in elevators and exhaust systems).

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

[0057]

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

[0059] Table 2 Process parameters

[0060]

[0061] Table 3 shows the performance indicators of the examples of the present invention and the comparative examples. The room temperature mechanics is tested according to GB / T 228.1 "Metallic material tensile test Part 1: Room temperature test method"; the high temperature mechanics is tested according to GB / T 228.2 "Metallic material tensile test Part 2: High temperature test method"; the grain is tested according to GBT 6394-2017 "Method for determination of average grain size of metals".

[0062] Table 3 Cold plate performance indicators

[0063]

[0064] Therefore, compared with the comparative example, the mechanical properties, room temperature yield strength, tensile strength, 320°C tensile strength and yield strength of the inventive example are improved.

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

[0066] The invention effectively improves the strength of ferritic stainless steel, effectively reduces cracks inside the ingot during ingot casting, and simultaneously improves the yield strength and tensile strength at room temperature and at 320°C.

[0067] It should be noted that, in this article, unless otherwise clearly specified and limited, the term "connection" or its synonyms should be understood in a broad sense. 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 directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. Moreover, expressions such as "first" and "second" 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. At the same time, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a process, method, article or device. In addition, "front", "back", "left", "right", "upper" and "lower" in this article are all referenced to the placement state 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, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing ferritic stainless steel with good high temperature strength and processability, characterized in that: The preparation method of the ferritic stainless steel with good high temperature strength and workability comprises: smelting-continuous casting-grinding-hot rolling-first annealing-cold rolling-second annealing-pickling, wherein the chemical composition of the ferritic stainless steel with good high temperature strength and 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%, and the balance is Fe and unavoidable impurities; Smelting: Smelt stainless steel into ferritic stainless steel liquid according to the chemical composition and mass percentage; Continuous casting: The molten steel is prepared into a continuous casting slab with a thickness of 200 mm, and the tundish temperature is 1545℃~1555℃; Grinding: hot grinding of continuous casting slabs at a temperature of 350°C to 550°C; Hot rolling: The continuous casting slab is heated to a temperature T 铸 =1180℃~1200℃, the continuous casting plate heating time is 200min~220min, and then the hot coil is obtained through rough rolling, finish rolling and coiling. The rough rolling temperature T 粗 =1040℃~1060℃, final rolling temperature T 终 =830℃~850℃, coiling temperature T 卷 =630℃~650℃, coiling thickness is 6mm; First annealing: Continuously anneal the hot coil at annealing temperature T 热退 =(870+2Cr+60Ti+30Al)℃, insulation 1.2min / mm; Cold rolling: cold rolling deformation rate 70% ~ 80%, the final cold plate thickness 1.4mm ~ 1.8mm; Second annealing: anneal the cold plate at annealing temperature T 冷退 =(845+2Cr+60Ti+30Al)℃, keep warm for 1min / mm.

2. The method for preparing ferritic stainless steel having good high temperature strength and workability as claimed in claim 1, characterized in that: The method also includes a pickling step for the steel plate after the second annealing is completed.

3. A ferritic stainless steel having good high temperature strength and workability, characterized in that: The chemical composition of the ferritic stainless steel with good high temperature strength and processability is controlled by mass percentage as follows: 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 is Fe and unavoidable impurities.

4. The ferritic stainless steel having excellent high temperature strength and workability according to claim 3, characterized in that: C: 0.008% to 0.014%, N: 0.008% to 0.012%, Si: 0.38% to 0.45%, Mn: 0.40% to 0.50%, P: 0.018% to 0.025%.

5. The ferritic stainless steel having excellent high temperature strength and workability according to claim 3, characterized in that: Ti: 0.33-0.40, N: 0.008-0.012, and Al is (0.10-0.12)*Ti.

6. The ferritic stainless steel having excellent high temperature strength and workability according to claim 3, characterized in that: The average grain size G is: 7.0 to 8.

0.

7. The ferritic stainless steel having excellent high temperature strength and workability according to claim 3, characterized in that: The yield strength at room temperature is: 290Mpa~310Mpa, the tensile strength is: 450Mpa~480Mpa, and the elongation is: 33%~38%; The yield strength at 320℃ is: 210Mpa~245Mpa, and the tensile strength is: 370Mpa~390Mpa.

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