0Cr15Ni5Cu4Nb stainless steel strip and preparation method thereof

Abstract

The invention relates to precipitation hardening stainless steel, in particular to a 0Cr15Ni5Cu4Nb stainless steel strip and a preparation method thereof. The 0Cr15Ni5Cu4Nb stainless steel comprises the following chemical components in percentage by mass: less than or equal to 0.05% of C, less than or equal to 1.00% of Si, less than or equal to 1.00% of Mn, 14.0-15.5% of Cr, 3.5-5.5% of Ni, 4.0-4.5% of Cu, 0.45% of Nb, less than or equal to 0.005% of S, less than or equal to 0.010% of P, less than or equal to 0.002% of O, less than or equal to 0.001% of N and the balance of Fe. The preparation method comprises the steps of smelting, coping forging, coping hot rolling, annealing treatment, acid pickling, coping cold rolling and solution treatment. By controlling the contents of the Cu element and the Nb element, a Cu phase and NbC are separated out through solution treatment of a finished product, and the hardness and the mechanical property of the material are enhanced.

Description

Technical Field

[0001] The invention relates to precipitation hardening stainless steel, in particular to a 0Cr15Ni5Cu4Nb stainless steel strip and a preparation method thereof. Background Art

[0002] 0Cr15Ni5Cu4Nb is a martensitic precipitation hardened stainless steel with good processing performance and dimensional stability. 0Cr15Ni5Cu4Nb steel has the characteristics of high strength, good transverse toughness, simple heat treatment process, small deformation, both performance and process performance, excellent mechanical properties and certain corrosion resistance. It has been widely used in key components such as aircraft and ships. With the rapid development of aviation technology, the proportion of steel used in aircraft has gradually decreased, so high-strength steel is needed to achieve weight reduction in flight parts structure. In recent years, the localization process of some (ultra) high-strength steel grades has entered an unprecedented rapid development stage, especially precipitation hardening stainless steel.

[0003] At present, the mechanical properties of domestic 0Cr15Ni5Cu4Nb bars are insufficient. Usually, the strength and hardness of the material are improved by increasing the nitrogen content, but the corrosion resistance is greatly reduced, which ultimately affects its service life. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problem that the corrosion resistance of the existing precipitation hardened stainless steel 0Cr15Ni5Cu4Nb is reduced and its service life is affected by increasing the nitrogen content to improve the strength and hardness of the material, and to provide a preparation method of 0Cr15Ni5Cu4Nb stainless steel and its strip.

[0005] To solve the above technical problems, the technical solutions provided by the present invention are as follows:

[0006] A 0Cr15Ni5Cu4Nb stainless steel, whose chemical composition, in terms of mass percentage, includes:

[0007] C≤0.05%, Si≤1.00%, Mn≤1.00%, Cr: 14.0-15.5%, Ni: 3.5-5.5%, Cu: 4.0-4.5%, Nb: 5 times the C content -0.45%, S≤0.005%, P≤0.010%, O≤0.002%, N≤0.001%, and the balance Fe.

[0008] Furthermore, its chemical composition, in terms of mass percentage, includes:

[0009] C: 0.03%-0.05%, Si≤0.50%, Mn≤0.70%, Cr: 14.0-15.5%, Ni: 3.5-5.5%, Cu: 4.2-4.35%, Nb: 5 times the C content-0.45%, S≤0.005%, P≤0.010%, O≤0.002%, N≤0.001%, and the balance Fe.

[0010] A method for preparing a 0Cr15Ni5Cu4Nb stainless steel strip comprises the following steps:

[0011] S1. Prepare the charge, melt the charge, and obtain a steel billet with the chemical composition after cooling;

[0012] S2, removing defects on the surface of the steel billet and keeping the steel billet warm;

[0013] After the insulation is completed, the steel billet is forged with a deformation amount of 5%-10%, the deformation amount is large at first and then small, the deformation rate is fast at first and then slow, the starting forging temperature is ≥1200℃, and the final forging temperature is ≥900℃;

[0014] After forging is completed, air cooling is performed to obtain the forging blank;

[0015] S3, grinding the forging blank to remove the oxide scale on the surface of the forging blank;

[0016] S4, heating the forging billet to 1200-1250°C and keeping it at that temperature for 5 hours;

[0017] After the insulation is completed, the forging billet is hot rolled, the starting rolling temperature is ≥1250°C, the final rolling temperature is ≥950°C, and the hot rolling is completed and water-cooled to obtain a hot-rolled billet;

[0018] S5, heating the hot-rolled slab to 1000-1050° C. and performing a solid solution treatment on the hot-rolled slab, wherein the solid solution treatment time is 30-60 minutes;

[0019] After the solution treatment is completed, the hot rolled billet is sequentially water cooled, pickled and ground to obtain an intermediate billet;

[0020] S6. Cold rolling and solution treatment are performed on the intermediate billet to obtain 0Cr15Ni5Cu4Nb stainless steel strip.

[0021] Furthermore, in step S1, the charge is chromium, nickel, copper, manganese, niobium, silicon, carbon and iron with a particle size of ≯20 mm.

[0022] Furthermore, in step S1, in the steel billet having chemical composition conforming thereto obtained after cooling, the O content is ≤0.002%, and the N content is ≤0.001%.

[0023] Furthermore, in step S2, the specific method for keeping the steel billet warm is:

[0024] Preheat the steel billet at 600-700℃ for 60min;

[0025] After preheating, the billet is heated to 800-850℃ at a heating rate of 50-80℃ / min and the initial heat preservation is carried out for 3h;

[0026] After the initial insulation is completed, the billet is heated to 1200-1250℃ at a heating rate of 50-80℃ / min and then subjected to secondary insulation for 5h.

[0027] Furthermore, in step S4, the thickness of the hot-rolled billet is 2.0-3.0 mm.

[0028] Furthermore, step S6 is specifically as follows:

[0029] S6.1. The intermediate billet is sent to a rolling mill for cold rolling. The total reduction rate of the cold rolling is 60%-85%, the rolling tension is 40-60KN, 4-8 passes are adopted and the reduction rate of the first pass is ≮25%, and a cold-rolled strip with a thickness of 0.6-1.6 mm is obtained;

[0030] No annealing is performed between passes;

[0031] S6.2. The cold-rolled strip is fed into a bright continuous annealing furnace at a strip speed of 0.4 to 0.6 m / min, and solution treated at 1040°C. After air cooling, 0Cr15Ni5Cu4Nb stainless steel strip is obtained.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The 0Cr15Ni5Cu4Nb stainless steel strip and the preparation method thereof provided by the present invention adjust the addition ratio of different alloy elements, adopt about 15% chromium to ensure the corrosion resistance of the steel, and about 5% nickel content can balance the matrix structure, so that the steel can obtain a martensitic structure at room temperature, while reducing the δ-ferrite in the steel, increasing the Cu and Nb contents, adding about 4% copper, which plays a strengthening role, and a small amount of niobium can form an MC phase with carbon, which plays a role of pinning the grain boundary and refining the grains; by adjusting the smelting method and reducing the gas content of the raw materials, the gas content is further controlled, and the non-metallic inclusions in the alloy material are reduced, wherein the O content is controlled to be less than 0.002%, and the N content is controlled to be less than 0.001% (the O and N contents in the existing 0Cr15Ni5Cu4Nb stainless steel strip are 0.005-0.15%); at the same time, the strength and hardness of the 0Cr15Ni5Cu4Nb stainless steel are improved by work hardening, which makes up for the defect of insufficient performance caused by not adding nitrogen.

[0034] 2. The preparation method of 0Cr15Ni5Cu4Nb stainless steel strip provided by the present invention adopts a suitable temperature for post-rolling heat treatment in order to make the carbides fully dissolved into the matrix and the grain size not coarse, thereby eliminating the influence of grain boundary element segregation and harmful precipitation phases generated during the thermal deformation cooling process, ensuring the mechanical properties while providing high-quality billets for subsequent cold rolling production. DETAILED DESCRIPTION

[0035] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments. 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 creative work are within the scope of protection of the present invention.

[0036] A 0Cr15Ni5Cu4Nb stainless steel, the chemical composition of which, in terms of mass percentage, includes: C≤0.05%, Si≤1.00%, Mn≤1.00%, Cr: 14.0-15.5%, Ni: 3.5-5.5%, Cu: 4.0-4.5%, Nb: 5 times the C content - 0.45%, S≤0.005%, P≤0.010%, O≤0.002%, N≤0.001%, and the balance Fe;

[0037] Alternatively, its chemical composition includes, by mass percentage: C: 0.03%-0.05%, Si≤0.50%, Mn≤0.70%, Cr: 14.0-15.5%, Ni: 3.5-5.5%, Cu: 4.2-4.35%, Nb: 5 times the C content - 0.45%, S≤0.005%, P≤0.010%, O≤0.002%, N≤0.001%, and the balance Fe.

[0038] Among them: C is used for deoxidation to increase the strength and hardness of the material, but a high C content will affect the corrosion resistance of stainless steel, so the C content is 0.03%-0.05%.

[0039] Cr is used to improve the corrosion resistance and strength of the material. The added Cr element will form a Cr2O3 film on the surface of the ingot, which protects the internal material. The corrosion resistance will be significantly enhanced with the increase of the Cr element content. However, too high Cr content is conducive to the precipitation of harmful phases and affects the stability of the mechanical properties of 0Cr15Ni5Cu4Nb stainless steel; therefore, the Cr content is 14.0-15.5%.

[0040] Mn is used to improve the forgeability (i.e., plasticity) of stainless steel, but too much Mn combined with the S element will generate MnS type inclusions at the grain boundaries, resulting in a decrease in the pitting corrosion resistance and intergranular corrosion resistance of the stainless steel. This solution reduces the adverse effects of Mn by reducing the S content, so the Mn content is less than 0.70%.

[0041] Ni is a key element for forming austenite and is used to stabilize the austenite structure. By adding the Ni element, the crystal structure of ferrite can be transformed from a body-centered cubic (BCC) structure to a face-centered cubic (FCC) structure, thereby improving the plasticity, weldability, toughness and other properties of stainless steel. Therefore, the Ni content is 3.5-5.5%.

[0042] Cu helps to strengthen the mechanical properties of 0Cr15Ni5Cu4Nb by precipitating copper phase steel through aging strengthening and improves corrosion resistance; therefore, the N content is 0.15-0.35%.

[0043] A method for preparing a 0Cr15Ni5Cu4Nb stainless steel strip comprises the following steps:

[0044] S1. Prepare the furnace charge, which includes metal chromium with a particle size of ≯20mm, electrolytic nickel, oxygen-free copper rod, metal manganese, pure iron, niobium rod, crystalline silicon, and graphite carbon;

[0045] The charge is melted and cooled to obtain a steel billet with chemical composition; in the steel billet, the O content is ≤0.002% and the N content is ≤0.001%;

[0046] S2. Grinding the surface of the steel billet to remove defects on the surface of the steel billet;

[0047] S3, preheating the steel billet after grinding at 600-700℃ for 60min;

[0048] After preheating, the billet is heated to 800-850℃ at a heating rate of 50-80℃ / min and the initial heat preservation is carried out for 3h;

[0049] After the initial heat preservation, the billet is heated to 1200-1250℃ at a heating rate of 50-80℃ / min and then subjected to secondary heat preservation for 5h.

[0050] After the secondary heat preservation is completed, the steel billet is forged with a deformation amount of 5%-10%, the deformation amount is large at first and then small, the deformation rate is fast at first and then slow, the starting forging temperature is ≥1200℃, and the final forging temperature is ≥900℃;

[0051] After forging is completed, air cooling is performed to obtain the forging blank;

[0052] S4, grinding the forging blank to remove the oxide scale on the surface of the forging blank; in order to remove the residual oxide scale chips after grinding, the surface of the forging blank after grinding is purged with compressed air, and the pressure of the compressed air is 0.2-0.5MPa;

[0053] S5. Heat the forging blank to 1200-1250°C at a heating rate of ≤100°C / min and keep it at that temperature for 5h;

[0054] After the insulation is completed, the forging billet is hot rolled, the starting rolling temperature is ≥1200°C, the final rolling temperature is ≥950°C, and the hot rolling is completed and then water-cooled to obtain a hot-rolled billet with a thickness of 2.0-3.0 mm;

[0055] S6, heating the hot-rolled slab to 1000-1050° C. and performing a solid solution treatment on the hot-rolled slab, wherein the solid solution treatment time is 30-60 minutes;

[0056] After the solution treatment is completed, the hot rolled billet is immediately water cooled, pickled and ground in sequence to obtain an intermediate billet;

[0057] S7. Cold rolling and solution treatment are performed on the intermediate billet to obtain 0Cr15Ni5Cu4Nb stainless steel strip:

[0058] S7.1, feeding the intermediate billet into the rolling mill for cold rolling, the total reduction rate of cold rolling is 60%-85%, the rolling tension is 40-60KN, 4-8 passes are adopted and the reduction rate of the first pass is ≮25%, and a cold-rolled strip with a thickness of 0.6-1.6mm is obtained;

[0059] No annealing is performed between passes;

[0060] S7.2. The cold-rolled strip is fed into a bright continuous annealing furnace at a strip speed of 0.4 to 0.6 m / min, and solution treated at 1040°C. After air cooling, 0Cr15Ni5Cu4Nb stainless steel strip is obtained.

[0061] Specific examples are given below.

[0062] Example 1

[0063] A method for preparing a 0Cr15Ni5Cu4Nb stainless steel strip comprises the following steps:

[0064] S1. Prepare the charge. The chemical composition of the charge includes, by mass percentage: C: 0.03%-0.05%, Si≤0.50%, Mn≤0.70%, Cr: 14.0-15.5%, Ni: 3.5-5.5%, Cu: 4.2-4.35%, Nb: 5 times the C content - 0.45%, S≤0.005%, P≤0.010%, O≤0.002%, N≤0.001%, and the balance Fe;

[0065] The charge is metal chromium with a particle size of ≯20mm, electrolytic nickel, oxygen-free copper rod, metal manganese, pure iron, niobium rod, crystalline silicon, and graphite carbon;

[0066] The charge is melted and cooled to obtain a steel billet with the chemical composition;

[0067] S2. Grinding the surface of the steel billet to remove defects on the surface of the steel billet;

[0068] S3, preheating the steel billet after grinding at 700°C for 60 minutes;

[0069] After preheating, the billet was heated to 830°C at a heating rate of 80°C / min and kept warm for the first time for 3h.

[0070] After the first heat preservation, the billet was heated to 1220°C at a heating rate of 80°C / min and then the second heat preservation was carried out for 5h.

[0071] After the secondary heat preservation is completed, the steel billet is forged with a deformation amount of 5%-10%, the deformation amount is large at first and then small, the deformation rate is fast at first and then slow, the starting forging temperature is ≥1200℃, and the final forging temperature is ≥900℃;

[0072] After forging is completed, air cooling is performed to obtain the forging blank;

[0073] S4, grinding the forging blank and blowing it with compressed air to remove the residual oxide scales from grinding;

[0074] S5, heating the forging blank to 1250°C at a heating rate of 90°C / min and keeping the temperature for 5h;

[0075] After the insulation is completed, the forging billet is hot rolled, the starting rolling temperature is ≥1200°C, the final rolling temperature is ≥950°C, and the hot rolling is completed and water-cooled to obtain a hot-rolled billet;

[0076] S6, heating the hot rolled slab to 1050°C and performing a solution treatment on the hot rolled slab, wherein the solution treatment time is 40 minutes;

[0077] After the solution treatment is completed, the hot rolled billet is immediately water cooled, pickled and ground in sequence to obtain an intermediate billet;

[0078] S7. Cold rolling and solution treatment are performed on the intermediate billet to obtain 0Cr15Ni5Cu4Nb stainless steel strip:

[0079] S7.1. The intermediate billet is sent to a rolling mill for cold rolling. The total reduction rate of the cold rolling is 75%, the rolling tension is 50 KN, 6 passes are adopted and the reduction rate of the first pass is ≮25%, and a cold-rolled strip with a thickness of 0.6 mm is obtained;

[0080] No annealing is performed between passes;

[0081] S7.2. The cold-rolled strip is fed into a bright continuous annealing furnace at a strip speed of 0.4 to 0.6 m / min, and solution treated at 1040°C. After air cooling, a 0Cr15Ni5Cu4Nb stainless steel strip with a thickness of 0.6 mm is obtained.

[0082] Example 2

[0083] The difference between Example 2 and Example 1 is that a 0Cr15Ni5Cu4Nb stainless steel strip with a thickness of 1.0 mm is obtained.

[0084] Example 3

[0085] The difference between Example 3 and Example 1 is that a 0Cr15Ni5Cu4Nb stainless steel strip with a thickness of 1.6 mm is obtained.

[0086] Comparative Example 1

[0087] The difference between Comparative Example 1 and Example 1 is that the Cu content is reduced to 0.33%; and a stainless steel strip with a thickness of 0.6 mm is obtained.

[0088] Comparative Example 2

[0089] Compared with Example 1, Comparative Example 2 differs in that the total cold rolling reduction is less than 60%, and annealing is performed between passes; a stainless steel strip with a thickness of 1.0 mm is obtained.

[0090] The chemical compositions of the 0Cr15Ni5Cu4Nb stainless steel strips prepared in Examples 1 to 3 and the stainless steel strips prepared in Comparative Examples 1 and 2 were tested, as shown in Table 1.

[0091] Table 1: Chemical composition

[0092]

[0093] Note: The oxygen content is controlled within 20ppm and the nitrogen content is controlled within 10ppm.

[0094] The room temperature tensile strength, room temperature yield strength, room temperature elongation and hardness of the 0Cr15Ni5Cu4Nb stainless steel strips prepared in Examples 1 to 3 and the stainless steel strips prepared in Comparative Examples 1 and 2 were tested respectively. The test results are shown in Table 2.

[0095] Table 2: Performance test table

[0096] Test items Specifications (mm) Tensile strength(MPa) Yield strength(MPa) Elongation(%) Hardness(HBW) 1 0.60 1157 1098 9.0％ 366 2 1.00 1163 1125 9.0％ 378 3 1.60 1132 1118 8.5％ 335 Comparative Example 1 0.60 1061 1053 6.0％ 306 Comparative Example 2 1.00 1059 1039 5.5％ 318

[0097] Combining Table 1 and Table 2, it can be seen that by increasing the Cu content in the stainless steel strip, the room temperature tensile strength, room temperature yield strength, room temperature elongation and hardness of the 0Cr15Ni5Cu4Nb stainless steel strip can be improved.

[0098] It can be seen from Table 2 that the 0Cr15Ni5Cu4Nb stainless steel strip prepared by the present invention has a tensile strength of ≥1132MPa, a yield strength of ≥1098MPa, and an elongation of ≥8.5%; compared with Comparative Examples 1 and 2, the tensile strength of the 0Cr15Ni5Cu4Nb stainless steel strip prepared by the present invention is increased by 9%, the yield strength is increased by 4%, the elongation is increased by 50%, and the hardness is increased by 18%.

[0099] In other embodiments of the present invention, the hot rolled billet is subjected to a hot rolling process with a deformation amount of 60%-85% in one rolling process.

[0100] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A 0Cr15Ni5Cu4Nb stainless steel strip, characterized in that: Its chemical composition, in terms of mass percentage, includes: C≤0.05%, Si≤1.00%, Mn≤1.00%, Cr: 14.0-15.5%, Ni: 3.5-5.5%, Cu: 4.0-4.5%, Nb: 5 times the C content -0.45%, S≤0.005%, P≤0.010%, O≤0.002%, N≤0.001%, and the balance Fe.

2. The 0Cr15Ni5Cu4Nb stainless steel strip according to claim 1, characterized in that: In terms of mass percentage, its chemical composition includes: C: 0.03%-0.05%, Si≤0.50%, Mn≤0.70%, Cr: 14.0-15.5%, Ni: 3.5-5.5%, Cu: 4.2-4.35%, Nb: 5 times the C content-0.45%, S≤0.005%, P≤0.010%, O≤0.002%, N≤0.001%, and the balance Fe.

3. A method for preparing 0Cr15Ni5Cu4Nb stainless steel strip, characterized in that: The steps include: S1. Prepare the charge, melt the charge, and obtain a steel billet with the chemical composition after cooling; S2, removing defects on the surface of the steel billet and keeping the steel billet warm; After the insulation is completed, the steel billet is forged with a deformation amount of 5%-10%, the deformation amount is large at first and then small, the deformation rate is fast at first and then slow, the starting forging temperature is ≥1200℃, and the final forging temperature is ≥900℃; After forging is completed, air cooling is performed to obtain the forging blank; S3, grinding the forging blank to remove the oxide scale on the surface of the forging blank; S4, heating the forging billet to 1200-1250°C and keeping it at that temperature for 5 hours; After the insulation is completed, the forging billet is hot rolled, the starting rolling temperature is ≥1200°C, the final rolling temperature is ≥950°C, and the hot rolling is completed and water-cooled to obtain a hot-rolled billet; S5, heating the hot-rolled slab to 1000-1050° C. and performing a solid solution treatment on the hot-rolled slab, wherein the solid solution treatment time is 30-60 minutes; After the solution treatment is completed, the hot rolled billet is sequentially water cooled, pickled and ground to obtain an intermediate billet; S6. Cold rolling and solution treatment are performed on the intermediate billet to obtain 0Cr15Ni5Cu4Nb stainless steel strip.

4. The method for preparing the 0Cr15Ni5Cu4Nb stainless steel strip according to claim 3, characterized in that: In step S1, the charge is chromium, nickel, copper, manganese, niobium, silicon, carbon and iron with a particle size of ≯20 mm.

5. The method for preparing the 0Cr15Ni5Cu4Nb stainless steel strip according to claim 3, characterized in that: In step S1, after cooling, the steel billet having chemical composition is obtained, wherein the O content is ≤0.002% and the N content is ≤0.001%.

6. The method for preparing the 0Cr15Ni5Cu4Nb stainless steel strip according to claim 3, characterized in that: In step S2, the specific method for keeping the steel billet warm is: Preheat the steel billet at 600-700℃ for 60min; After preheating, the billet is heated to 800-850℃ at a heating rate of 50-80℃ / min and the initial heat preservation is carried out for 3h; After the initial insulation is completed, the billet is heated to 1200-1250℃ at a heating rate of 50-80℃ / min and then subjected to secondary insulation for 5h.

7. The method for preparing the 0Cr15Ni5Cu4Nb stainless steel strip according to claim 3, characterized in that: In step S4, the thickness of the hot-rolled billet is 2.0-3.0 mm.

8. The method for preparing 0Cr15Ni5Cu4Nb stainless steel strip according to claim 3, characterized in that: Step S6 is specifically as follows: S6.

1. The intermediate billet is sent to a rolling mill for cold rolling. The total reduction rate of the cold rolling is 60%-85%, the rolling tension is 40-60KN, 4-8 passes are adopted and the reduction rate of the first pass is ≮25%, and a cold-rolled strip with a thickness of 0.6-1.6 mm is obtained; No annealing is performed between passes; S6.

2. The cold-rolled strip is fed into a bright continuous annealing furnace at a strip speed of 0.4 to 0.6 m / min, and solution treated at 1040°C. After air cooling, 0Cr15Ni5Cu4Nb stainless steel strip is obtained.

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