15-5PH stainless steel cold-rolled sheet and preparation method thereof

Abstract

The invention relates to a 15-5PH stainless steel cold-rolled sheet and a preparation method thereof, belongs to the technical field of precipitation hardening stainless steel sheets, and solves the problem that the performance and the sheet shape of a 15-5PH stainless steel cold-rolled sheet obtained by a conventional preparation method do not meet requirements. The method comprises the following steps: carrying out acid pickling and water washing on a plate blank subjected to softening heat treatment by adopting hydrofluoric acid liquid, carrying out cold rolling, carrying out solid solution heat treatment, carrying out acid pickling and water washing by adopting hydrofluoric acid liquid, and carrying out cold flattening. According to the method, acid pickling can be carried out at low temperature, and oxidation impurities on the surface of the thin plate can be completely removed under the condition that the structure evolution of the thin plate is not caused; hydrofluoric acid liquor can be cleaned through washing operation after acid pickling, generation of subsequent new oxidation impurities is avoided, the straight plate shape of the thin plate subjected to subsequent high-precision rolling and cold leveling is guaranteed, and the problem that actual application is affected due to the fact that the precision of the 15-5PH thin plate is poor is solved.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel sheets, and in particular to a 15-5PH stainless steel cold-rolled sheet and a preparation method thereof. Background Art

[0002] 15-5PH material is a martensitic precipitation hardening stainless steel. Due to its high strength and good corrosion resistance, it is widely used in the manufacture of aircraft structures. Among them, 15-5PH thin plate is the raw material for key components of large aircraft, and has extremely high requirements on performance and plate shape.

[0003] However, in the process of preparing 15-5PH thin plates using the current stainless steel thin plate preparation process, due to the high strength and high hardness of the stainless steel, it is easy to develop wave shape and warping during the cold rolling process, and cracking may occur in severe cases; and the pickling process before cold rolling is also very important. The traditional combination of high-temperature alkali washing + sulfuric acid pickling for removing the oxide scale on the surface of heat-treated precipitation hardened stainless steel will affect the cold rolling effect of the intermediate billet of the small thickness 15-5PH thin plate when the oxide layer is removed, thereby affecting the performance and plate shape of the final product, and aggravating the undesirable plate shape phenomenon.

[0004] Therefore, a new method for preparing 15-5PH stainless steel cold-rolled thin plate is urgently needed to ensure that the performance and plate shape of the obtained thin plate meet the requirements and solve the problem that the current 15-5PH thin plate is affected by poor precision and thus has an impact on practical application. Summary of the invention

[0005] In view of the above analysis, an embodiment of the present invention aims to provide a 15-5PH stainless steel cold-rolled sheet and a preparation method thereof, so as to solve at least one of the problems that the performance and plate shape of the 15-5PH stainless steel cold-rolled sheet obtained by the conventional preparation method do not meet the requirements.

[0006] On the one hand, an embodiment of the present invention provides a method for preparing a 15-5PH stainless steel cold-rolled sheet, the method comprising:

[0007] (1) Softening heat treatment of the slab;

[0008] (2) pickling and water washing the slab after softening heat treatment, wherein the pickling acid solution is a hydrofluoric acid solution;

[0009] (3) cold rolling the washed slab;

[0010] (4) repeating steps (1) to (3) until the size of the slab meets the requirements, thereby obtaining a crude product;

[0011] (5) subjecting the crude product to a solution heat treatment;

[0012] (6) pickling and water washing the crude product after the solution heat treatment, wherein the pickling acid solution is a hydrofluoric acid solution;

[0013] (7) cold treatment of the crude product after pickling;

[0014] (8) The crude product after cold flat treatment is degreased and finely processed.

[0015] Furthermore, the 15-5PH stainless steel cold-rolled sheet is a 15-5PH precipitation hardened stainless steel cold-rolled sheet with a thickness of 1-4 mm.

[0016] Furthermore, in step (2), the hydrofluoric acid solution is an aqueous solution of hydrofluoric acid and nitric acid, wherein the concentration of the hydrofluoric acid is 3-5%, and the concentration of the nitric acid is 24-30%.

[0017] Furthermore, in step (2), the pickling temperature is 20-25° C. and the time is 10-60 min.

[0018] Furthermore, in step (2), the water washing method is cold water washing + hot water washing.

[0019] Furthermore, in step (4), repeat 1-3 times.

[0020] Furthermore, in step (6), the hydrofluoric acid solution is an aqueous solution of hydrofluoric acid and nitric acid, wherein the concentration of the hydrofluoric acid is 3-5%, and the concentration of the nitric acid is 24-30%.

[0021] Furthermore, in step (6), the pickling temperature is 20-25° C. and the time is 10-60 min.

[0022] Further, calculated according to mass percentage, the element composition of the 15-5PH stainless steel includes: C: 0-0.07%, Mn: 0-1.00%, Si: 0-1.00%, P: 0-0.03%, S: 0-0.015%, Cr: 14.00-15.50%, Ni: 3.50-5.50%, Nb: 5C-0.45%, Cu: 2.50-4.50%, Mo: 0-0.50%, and the balance is Fe.

[0023] On the other hand, an embodiment of the present invention provides a 15-5PH stainless steel cold-rolled sheet, which is produced by the above method.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0025] 1. The study found that the use of traditional high-temperature alkali washing and / or pickling methods will lead to high-temperature microstructure evolution or incomplete cleaning or acid residue, thereby affecting the accuracy of subsequent cold rolling of the intermediate billet of the thin plate or subsequent cold flat treatment of the finished product, and ultimately affecting product performance and plate shape. The present invention uses hydrofluoric acid solution for pickling and water washing steps after pickling, which will overcome the above problems and achieve high-precision preparation of 15-5PH precipitation hardened stainless steel sheets.

[0026] In addition, in order to maintain the performance and shape of the 15-5PH precipitation hardened stainless steel sheet, the present invention adopts a multi-stage cold rolling method to reduce the residual stress in the plate as much as possible to maintain the stability of the performance and shape; the present invention performs a cold flattening treatment on the rough product after solution heat treatment after rolling to straighten the bend that may occur during the solution heat treatment process, so that the product plate flatness meets the requirements.

[0027] 2. The present invention achieves thorough removal of oxidized impurities and other pollutants on the surface of 15-5PH thin plates at low temperatures by regulating the concentrations of hydrofluoric acid and nitric acid in the hydrofluoric acid pickling solution and the ratio of the two, and avoids excessive corrosion of the thin plate surface. In addition, in the subsequent cold rolling or cold flat treatment process, it is ensured that large bending, warping and other poor plate shapes, changes in internal organizational morphology and the like do not occur.

[0028] 3. The present invention adjusts the temperature and time of hydrofluoric acid pickling to completely remove oxidized impurities and other pollutants on the surface of the 15-5PH thin plate, thereby avoiding overoxidation, overacidity and incomplete acid cleaning during the pickling process, thereby ensuring the surface quality of the pickled product.

[0029] 4. The present invention adopts a two-stage water washing method to remove the hydrofluoric acid pickling solution remaining on the surface of the 15-5PH thin plate after pickling, wherein the cold water washing removes the oxides that cannot fall off naturally after pickling and a small amount of residual acid attached, and the hot water washing removes the residual acid. The two-stage water washing of cold water washing + hot water washing can avoid the residual hydrofluoric acid pickling solution after pickling, which leads to the formation of a new oxide layer in the later stage, improves the subsequent cold rolling or cold flat treatment effect, and improves the precision of the thin plate product.

[0030] 5. The pickling of the 15-5PH thin plate after heat treatment with hydrofluoric acid solution can be carried out under low temperature conditions, which is far lower than the temperature of the transformation of the microstructure of 15-5PH stainless steel (≥480°C), so that the oxidized impurities on the surface of the thin plate can be completely removed while ensuring the performance of the thin plate; the water washing operation after the pickling can clean the hydrofluoric acid solution, avoid the subsequent generation of new oxidized impurities, and is beneficial to the subsequent high-precision rolling and cold flat treatment, ensuring the flat plate shape of the 15-5PH stainless steel thin plate, so as to solve the problem that the current thin plate has poor precision and affects practical application.

[0031] 6. Before the multi-pass cold rolling process of the 15-5PH stainless steel sheet of the present invention, the intermediate billet after each softening can be pickled using the pickling solution and pickling process provided by the present invention, and the crude product before cold flat treatment can also be pickled using the pickling solution and pickling process, which simplifies the process and facilitates subsequent waste liquid treatment.

[0032] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0034] Figure 1 This is the appearance of the 15-5PH slab A-1 after pickling with hydrofluoric acid solution in Example 1;

[0035] Figure 2 This is the appearance of the 15-5PH slab A-2 of Comparative Example 1 after pickling with hydrofluoric acid solution;

[0036] Figure 3 This is the appearance of the 15-5PH slab A-3 of Comparative Example 2 after pickling with hydrofluoric acid solution;

[0037] Figure 4 This is an appearance diagram of the 15-5PH slab 1 after softening heat treatment and pickling with hydrofluoric acid solution in Example 2;

[0038] Figure 5 This is the appearance and plate type diagram of the 15-5PH thin plate rough product 1 after cold rolling in Example 2;

[0039] Figure 6 This is the appearance of the 15-5PH thin plate crude product 1 after solution heat treatment and pickling with hydrofluoric acid solution in Example 2;

[0040] Figure 7 This is the appearance of the 15-5PH thin plate rough product 1 after cold flat treatment in Example 2;

[0041] Figure 8 This is the appearance of the 15-5PH slab 2 of Comparative Example 3 treated by the conventional high-temperature alkali washing + acid washing combination method;

[0042] Fig. 9 This is the appearance of the 15-5PH sheet rough product 2 after cold rolling of comparative example 3;

[0043] Fig.10 This is the plate type diagram of the 15-5PH thin plate rough product 2 after cold rolling in comparative example 3;

[0044] Fig.11 This is the appearance of the 15-5PH thin plate crude product 3 treated by the conventional high-temperature alkali washing + acid washing combination method in comparative example 4;

[0045] Fig.12 This is the appearance of the 15-5PH slab 5 of Comparative Example 6 after pickling with hydrofluoric acid solution;

[0046] Fig.13 This is the appearance of the 15-5PH slab 6 of comparative example 7 after pickling with hydrofluoric acid solution. DETAILED DESCRIPTION

[0047] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0048] In the process of preparing 15-5PH thin plates using the current stainless steel thin plate preparation process, due to the high strength and high hardness of the stainless steel, it is easy to appear wavy and warping during the cold rolling process, and cracking may occur in severe cases; and the pickling process before cold rolling is also very important. The traditional combination of high-temperature alkali washing + sulfuric acid pickling for removing the oxide scale on the surface of heat-treated precipitation hardened stainless steel will affect the cold rolling effect of the intermediate billet of the small thickness 15-5PH thin plate when the oxide layer is removed, causing the thin plate after cold rolling to show poor plate shape such as slight bulging and wavy shape, thereby affecting the performance and plate shape of the final product and aggravating the poor plate shape phenomenon.

[0049] Therefore, the present invention provides a method for preparing a 15-5PH stainless steel cold-rolled sheet, the method comprising:

[0050] (1) Softening heat treatment of the slab;

[0051] (2) pickling and water washing the slab after softening heat treatment, wherein the pickling acid solution is a hydrofluoric acid solution;

[0052] (3) cold rolling the washed slab;

[0053] (4) repeating steps (1) to (3) until the size of the slab meets the requirements, thereby obtaining a crude product;

[0054] (5) subjecting the crude product to solution heat treatment;

[0055] (6) pickling and water washing the crude product after the solution heat treatment, wherein the pickling acid solution is a hydrofluoric acid solution;

[0056] (7) cold treatment of the crude product after pickling;

[0057] (8) The crude product after cold flat treatment is degreased and finely processed.

[0058] Specifically, in step (1), in order to ensure that the stainless steel has good plasticity and processing properties before cold rolling, the slab is first subjected to a softening heat treatment.

[0059] It should be noted that the softening heat treatment may be a heat treatment method such as solution heat treatment, annealing heat treatment, etc.

[0060] According to a preferred embodiment of the present invention, the softening heat treatment may be an annealing heat treatment at a temperature of 600° C. for a time of not less than 10 h.

[0061] It should be noted that in order to remove the oxide scale, rust and other impurities on the surface of the slab after the softening heat treatment, improve the surface quality of the product, and improve the quality of subsequent cold rolling, the slab after the softening heat treatment needs to be pickled.

[0062] The inventors found in the process of preparing 15-5PH stainless steel sheets that in the process of removing oxidized impurities and pollutants on the surface of 15-5PH stainless steel sheets by the traditional high-temperature alkali washing method, the 15-5PH stainless steel sheets will undergo uncontrollable organizational evolution due to excessively high temperatures, thereby affecting the performance and plate shape of the final product; and the traditional pickling method using inorganic acids such as hydrochloric acid and sulfuric acid often faces problems such as incomplete cleaning after multiple picklings, acid solution easily remaining to cause the formation of a new oxide layer, high cost and low efficiency, which affects the subsequent cold rolling effect of the 15-5PH thin plate straight plate shape. Therefore, the present invention uses hydrofluoric acid solution to pickle the slab after heat treatment.

[0063] Specifically, in step (2), the heat-treated slab is first pickled with hydrofluoric acid solution and then washed with water.

[0064] Furthermore, the hydrofluoric acid solution in step (2) is an aqueous solution of hydrofluoric acid and nitric acid, wherein the concentration of hydrofluoric acid is 3-5%, which can be 3%, 3.5%, 4%, 4.5%, and 5%; the concentration of nitric acid is 24-30%, which can be 24%, 25%, 26%, 27%, 28%, and 29%; the molar ratio of hydrofluoric acid to nitric acid is 1:1-2.5, which can be 1:2, 2:3, 3:7, 4:7, and 5:7, so as to achieve thorough removal of oxidized impurities and other contaminants on the surface of the 15-5PH thin plate at low temperature, and ensure that no large bending, warping, and other poor plate shapes and internal components occur. If the concentration of hydrofluoric acid / nitric acid is too high, it will cause excessive corrosion on the surface of the thin plate, affecting the surface quality, increasing the difficulty of subsequent cleaning and waste liquid treatment, polluting the environment and increasing costs; if the concentration of hydrofluoric acid / nitric acid is too low, the pickling ability will decrease, the pickling will be uneven, affecting the surface quality of the product and subsequent processing, and prolonging the pickling time; if the proportion of hydrofluoric acid is too high, over-acid reaction will occur, the pickling reaction will be too violent and sensitive to temperature and time, resulting in uncontrolled pickling process; if the proportion of nitric acid is too high, the subsequent passivation reaction will be uneven, affecting the uniformity of product surface color.

[0065] Furthermore, in step (2), the pickling temperature range is 20-25°C. Different from the conventional high-temperature alkaline washing method, the present invention uses hydrofluoric acid solution to remove oxidized impurities and other pollutants on the surface of 15-5PH stainless steel sheet at a relatively low temperature, thereby reducing energy consumption and cost while ensuring the performance of the sheet.

[0066] According to a preferred embodiment of the present invention, the temperature for pickling the 15-5PH stainless steel sheet with hydrofluoric acid solution is 20°C.

[0067] Furthermore, in step (2), the present invention adopts hydrofluoric acid solution for pickling for 10-60 minutes. If the time is too long, it will lead to over-acid reaction, macroscopically appearing waves, bulges and other poor plate shape phenomena. If the time is too short, it will lead to uneven removal of the surface oxide layer, affecting subsequent rolling, cooling and other processes, thereby affecting product performance and surface quality.

[0068] According to a preferred embodiment of the present invention, the pickling time using hydrofluoric acid solution is 10 minutes, 30 minutes, 40 minutes and 60 minutes respectively.

[0069] Furthermore, in step (2), in order to remove the hydrofluoric acid pickling solution remaining on the surface of the 15-5PH thin plate after pickling, the present invention adopts a two-stage water washing method, including cold water washing and hot water washing, to avoid the residual hydrofluoric acid pickling solution after pickling leading to the formation of a new oxide layer in the later stage, thereby improving the subsequent cold rolling or cold flat treatment effect and improving the precision of the thin plate product.

[0070] It should be noted that the present invention adopts the method of placing the entire plate into a water tank and swinging it to complete water washing, and cold water (10-25°C) is used to rinse to remove the oxides that cannot fall off naturally after pickling and a small amount of residual acid that is attached, and hot water (>70°C) is used to rinse to remove the residual acid. Only by combining cold water rinsing with hot water rinsing can a smooth surface be achieved without black oxides or acid residues.

[0071] It should be noted that, further, before the pickling in step (2), the 15-5PH thin plate after heat treatment is cooled, and the cooling method is air cooling, furnace cooling, wind cooling or water cooling, and the thin plate is cooled to room temperature before pickling.

[0072] The inventors found in their research that, due to the high strength and hardness of 15-5PH precipitation-hardened stainless steel, it is prone to wave shape and warping during the cold rolling process, and cracking may occur in severe cases. In addition, the heat treatment after cold rolling has a great influence on the plate shape, aggravating the phenomenon of poor plate shape. The small thickness of 15-5PH thin plate (<4mm) increases the difficulty of rolling, making the plate shape more deformed after heat treatment, increasing the difficulty of controlling the performance and plate shape. The small thickness of 15-5PH thin plate (<4mm) increases the difficulty of rolling, making the plate shape more deformed after heat treatment, increasing the difficulty of controlling the performance and plate shape. In addition, the high-temperature microstructure evolution or incomplete cleaning or residual acid caused by traditional high-temperature alkali washing and / or pickling methods have a greater impact on the subsequent cold rolling treatment of the small-thickness intermediate billet or the subsequent cold flat treatment of the finished product.

[0073] Specifically, the 15-5PH stainless steel sheet is a 15-5PH precipitation hardened stainless steel sheet with a thickness of 1-4 mm.

[0074] According to a preferred embodiment, the thicknesses of the thin plates are 4 mm, 2.8 mm, 1.8 mm, and 1.27 mm, respectively.

[0075] Specifically, in step (3), in order to make the final product achieve the expected performance and dimensional accuracy, the present invention requires cold rolling the slab.

[0076] It should be noted that, in order to achieve the target thickness of the final product, the present invention may also perform multiple stages of cold rolling on a cold rolling mill to minimize the impact of residual stress in the plate on subsequent processes, thereby maintaining the stability of performance and plate shape.

[0077] Specifically, in step (4), steps (1) to (3) are repeated until the size of the slab meets the requirements, thereby obtaining a crude product.

[0078] It should be noted that in order to maintain the performance and shape of the 15-5PH stainless steel sheet, the present invention needs to adjust the number of cold rolling stages of the slab according to the thickness of the raw material slab and the target thickness.

[0079] Furthermore, in step (4), the number of repeated stages is 1-3 times, that is, the total rolling process is ≤ 3 stages of cold rolling.

[0080] It should be noted that in order to maintain the performance and shape of the 15-5PH stainless steel sheet, it is necessary to control the number of cold rolling passes and the reduction of each cold rolling pass.

[0081] Specifically, in step (3), the reduction amount of each cold rolling pass is gradually reduced according to the pass, and the maximum does not exceed 0.5 mm.

[0082] It should be noted that 15-5PH thin plate, as the raw material for key components of large aircraft, is required to be delivered in a solid solution state, so solution heat treatment must be performed.

[0083] Specifically, in step (5), the present invention performs a solution heat treatment on the raw product after cold rolling, wherein the temperature of the solution heat treatment is 1040° C. and the time is 20 minutes.

[0084] It should be noted that, since the thin 15-5PH thin plate is sensitive to internal stress and easily shows signs of bending, the solution heat treatment of the rough finished product is very likely to cause the plate shape to bend, making it unable to meet the delivery requirements. Therefore, the plate shape of the thin plate after the solution heat treatment is straightened by adding a cold flattening process. In addition, in order to remove the oxidized impurities generated on the surface of the thin plate product during the solution heat treatment process and improve the surface quality and plate shape of the finished product, the rough finished product that has completed cold rolling needs to be pickled and cleaned first, and then cold flattened.

[0085] Specifically, in step (6), the present invention uses hydrofluoric acid solution to pickle and wash the crude product after the solution heat treatment.

[0086] It should be noted that the process of pickling and washing the crude product after the solution heat treatment with hydrofluoric acid solution in step (6) is the same as the process of pickling and washing the crude product after the softening heat treatment in step (2).

[0087] Specifically, the hydrofluoric acid solution in step (6) of the present invention is an aqueous solution of hydrofluoric acid and nitric acid, wherein the concentration of the hydrofluoric acid is 3-5%, and the concentration of the nitric acid is 24-30%;

[0088] Specifically, the pickling temperature in step (6) of the present invention is 20-25° C. and the time is 10-60 min.

[0089] Specifically, the water washing method in step (6) of the present invention is cold water washing + hot water washing.

[0090] Specifically, in order to ensure both the performance and the shape of the 15-5PH stainless steel sheet, the present invention controls the number of cold flattening passes to 1-7 times. If too few passes are performed, the flatness of the product cannot meet the requirements. If too many passes are performed, the mechanical properties (such as strength) of the product exceed the standard requirements.

[0091] It should be noted that in order to improve the surface uniformity and corrosion resistance of the 15-5PH slab or product, the present invention also performs subsequent improvement treatment on the thin plate after hydrofluoric acid pickling, and then performs the next process after water washing, such as cold rolling or cold flat treatment.

[0092] Specifically, in order to make the surface of the thin plate cleaner and more beautiful, the present invention performs high-temperature passivation on the thin plate after pickling in step (2) to form a film to protect the surface. The specific operation is: use 22-28% sulfuric acid for passivation, control the temperature between 45°C and 65°C, and the passivation time does not exceed 2 minutes.

[0093] It should be noted that the cold flattening and straightening process of the product is the final step for product delivery and plate shape control. Lubricating oil is required to ensure that no additional scratches or other impurities are generated during the cold flattening process to ensure the surface quality of the product. Therefore, after the thin plate product is cold flattened, the product needs to be deoiled to improve the surface quality of the finished product, and fine processing after deoiling, including grinding and shearing, is required.

[0094] The inventor found that when adjusting the preparation process of 15-5PH stainless steel sheet, changing the pickling process to hydrofluoric acid pickling was of great help to the subsequent secondary (or tertiary) cold rolling and cold flattening process. Hydrofluoric acid pickling will not cause changes in the internal structure and can also remove surface impurities. Therefore, after the hydrofluoric acid pickling, the plate type is basically kept straight and there is no obvious wave trend on the surface. Even if the sheet is bent due to uneven heating and inevitable residual stress in the plate during the solution heat treatment, the cold flattening pass and the cold flattening amount can be easily straightened to achieve the required flatness in the subsequent cold flattening process, which can meet the performance requirements of the product.

[0095] Specifically, calculated according to mass percentage, the element composition of the 15-5PH stainless steel of the present invention includes: C: 0-0.07%, Mn: 0-1.00%, Si: 0-1.00%, P: 0-0.03%, S: 0-0.015%, Cr: 14.00-15.50%, Ni: 3.50-5.50%, Nb: 5C-0.45%, Cu: 2.50-4.50%, Mo: 0-0.50%, and the balance is Fe.

[0096] According to a preferred embodiment of the present invention, calculated by mass percentage, the elements constituting the 15-5PH stainless steel include: C 0.042%, Mn 0.43%, Si 0.41%, P 0.022%, S 0.0013%, Cr 15.15%, Ni4.05%, Nb 0.31%, Cu 3.31%, Mo 0.080%, and the balance is F; or the elements of the 15-5PH stainless steel include: C: 0.042%, Mn: 0.44%, Si: 0.48%, P: 0.021%, S: 0.0018%, Cr: 15.16%, Ni: 4.10%, Nb: 0.31%, Cu: 3.23%, Mo: 0.061%, and the balance is Fe.

[0097] The present invention also provides a 15-5PH stainless steel cold-rolled thin plate, which is produced by the above method.

[0098] Specifically, calculated by mass percentage, the element composition of the 15-5PH stainless steel sheet includes: C: 0-0.07%, Mn: 0-1.00%, Si: 0-1.00%, P: 0-0.03%, S: 0-0.015%, Cr: 14.00-15.50%, Ni: 3.50-5.50%, Nb: 5C-0.45%, Cu: 2.50-4.50%, Mo: 0-0.50%, and the balance is Fe; the performance indicators of the 15-5PH stainless steel sheet are: tensile strength ≤1276Mpa, yield strength ≤1103Mpa, elongation after fracture (G=50.8mm) ≥3%, and straightness ≤19.05mm / m.

[0099] The technical solution of the present invention is further explained below in conjunction with specific embodiments.

[0100] Example 1

[0101] (1) At a temperature of 20° C., the 15-5PH slab A cooled to room temperature after annealing heat treatment is pickled with hydrofluoric acid solution, and the pickling method is immersion; wherein the hydrofluoric acid solution includes 4% HF and 28% HNO3. According to the mass percentage calculation, the chemical composition of the 15-5PH slab A used in this embodiment includes: C 0.042%, Mn 0.43%, Si 0.41%, P0.022%, S0.0013%, Cr 15.15%, Ni 4.05%, Nb 0.31%, Cu 3.31%, Mo 0.080%, and the balance is Fe; the sheet size is 30×200 mm, and the thickness is 3.18 mm.

[0102] (2) At a temperature of 45° C., the thin plate was passivated with a 20% sulfuric acid solution for 2 minutes; the passivated thin plate was subjected to secondary water washing, specifically: firstly placed in a cold water tank (15° C.) for 3 minutes of swing washing, and then placed in a hot water tank (75° C.) for 3 minutes of swing washing, to obtain a 15-5PH slab A-1 after pickling;

[0103] During the experiment, when the pickling in step (1) was carried out for 6 minutes, the oxide scale on the surface of the thin plate could be clearly observed to fall off, such as Figure 1 (a); when the immersion is continued for 10 minutes, the thin plate is taken out and rinsed with cold water in step (2), it can be found that the oxide scale on the surface of the thin plate 1 is completely removed, as shown in FIG. Figure 1 (b) as shown.

[0104] Comparative Example 1

[0105] The same method as Example 1 is used, except that in step (1), the 15-5PH slab A is heated by soaking in hot water at 40°C, and then pickled with hydrofluoric acid at 20°C to finally obtain the pickled 15-5PH slab A-2.

[0106] During the experiment, when the pickling in step (1) was carried out for 10 minutes, the thin plate was taken out and obvious oxidation marks were observed, such as Figure 2 (a); the oxidized spots can be washed away by acid washing again in the subsequent step (2), but after the cold water washing in step (2), the surface of the thin plate 2 is not completely cleaned by the acid, such as Figure 2 (b) as shown.

[0107] Comparative Example 2

[0108] The same method as in Example 1 was used, except that in step (1), the hydrofluoric acid solution included 4% HF and 10% HNO3, and finally a 15-5PH slab A-3 after pickling was obtained.

[0109] During the experiment, when the pickling in step (1) was carried out for 10 minutes, it was obviously seen that the oxide scale on the surface of the thin plate did not fall off completely. Figure 3 As shown in (a), it takes at least 40 minutes to basically remove the oxide layer; however, after the cold water rinse in step (2), it can still be clearly observed that the black oxide scale that has not been removed is attached to the surface of the thin plate 3, such as Figure 3 (b) as shown.

[0110] Example 2

[0111] (1) The 15-5PH slab 1 is subjected to annealing heat treatment at 600°C for 10 hours; wherein, according to the calculation by mass percentage, the chemical composition of the 15-5PH slab 1 includes: C: 0.042%, Mn: 0.44%, Si: 0.48%, P: 0.021%, S: 0.0018%, Cr: 15.16%, Ni: 4.10%, Nb: 0.31%, Cu: 3.23%, Mo: 0.061%, and the balance is Fe; the sheet size is 1000×2000mm, the thickness is 1.8mm, the tensile strength is 1070Mpa, the yield strength is 775Mpa, and the elongation after fracture (G=50.8mm) is 5%;

[0112] (2) The annealed slab is cooled to room temperature, and the 15-5PH slab 1 after annealing heat treatment is placed in a pickling tank for pickling by hoisting the whole slab. The mixed pickling solution includes 4% HF and 28% HNO3. Pickling is performed at a temperature of 20°C. In the initial stage, obvious yellow smoke can be observed, accompanied by a large number of bubbles, and the reaction is violent. After about 10 minutes, the bubbles and smoke decrease, and after about 20 minutes, only a small amount of bubbles are generated, and the degree of reaction is significantly reduced. Pickling is continued for 40 minutes and then taken out;

[0113] At 20°C, the thin plate was passivated for 2 minutes using a 20% sulfuric acid solution.

[0114] The passivated sheet was subjected to secondary water washing, specifically: firstly placed in a cold water tank (15°C) for swing washing for 3 minutes, and then placed in a hot water tank (75°C) for swing washing for 3 minutes, to obtain a 15-5PH sheet 1 to be cold rolled;

[0115] Through observation, the oxide layer on the surface of the 15-5PH slab 1 to be cold-rolled is completely detached and appears light grayish white. Figure 4 As shown, there is no acid residue on the surface, meeting the requirements of product surface quality;

[0116] (3) The 15-5PH slab 1 is cold rolled to obtain a 15-5PH thin plate rough product 1 with a thickness of 1.27 mm. The specific process parameters are: a rolling mill with a roller crown of 0.5, a working roll diameter of 390 mm, and a support roll diameter of 1250 mm is used for rolling at a speed of 0.8 m / s and a rolling force of 1200 tons. The target thickness of the first stage is 1.27±0.1 mm, the surface is smooth, and the plate shape is straight, such as Figure 5 As shown;

[0117] (4) subjecting the 15-5PH sheet crude product 1 to solution heat treatment at 1040°C for 20 min;

[0118] (5) The 15-5PH thin plate crude product 1 after solution heat treatment is pickled by the same method as step (2) to obtain a 15-5PH thin plate crude product 1, such as Figure 6 As shown;

[0119] Through observation, the oxide layer on the surface of the 15-5PH thin plate rough product 1 after solution heat treatment is completely detached, and the surface is bright metallic color. Except for the inevitable scratches caused by manual handling during the factory process, there is no acid residue, oxide and other impurities on the surface, which meets the requirements of product surface quality.

[0120] (6) The 15-5PH thin plate rough product 1 obtained in step (5) is subjected to cold flattening treatment. The specific operation is: controlling the roller speed to 0.8 m / s, the rolling force to 1200 tons, and the rolling pass to 7 passes. The final cold flattening amount is not higher than 0.05 mm, and the 15-5PH thin plate product 1 is obtained. The straightness is 8.0 mm / m. The final macroscopic plate shape is observed by naked eyes and has almost no plate shape defects such as bending and warping. Figure 7 As shown;

[0121] After subsequent degreasing and other factory processes, the product's tensile strength was measured to be 1040 MPa, the yield strength was 950 MPa, and the elongation after fracture (G=50.8 mm) was 8.09%.

[0122] Comparative Example 3

[0123] The same method as Example 2 is adopted, except that: in step (2), after the annealed 15-5PH slab 1 is cooled to room temperature, the slab 1 is cleaned by high-temperature alkali washing + traditional pickling method, specifically: first alkali washing in an industrial alkali washing tank mixed with 70%-80% sodium hydroxide and 20%-30% sodium nitrate at 400°C for 10 minutes, and then placed in a sulfuric acid + sodium nitrate + water mixed pickling tank (acid concentration 28-35%) for pickling, and finally a 15-5PH slab 2 to be cold rolled is obtained.

[0124] Through observation, the surface of 15-5PH slab 2 has obvious bulges, such as Figure 8 shown.

[0125] Step (3) The 15-5PH slab 2 is cold rolled using the same cold rolling process as step (3) of Example 2 to obtain a 15-5PH thin plate rough product 2 with a thickness of 1.33 mm; obvious scratches on the surface of the 15-5PH thin plate rough product 2 due to excessive correction can be observed with the naked eye, such as Fig. 9 As shown in the figure, the plate is obviously curved when viewed from the side. Fig.10 shown.

[0126] Comparative Example 4

[0127] The same method as in Example 2 is adopted, except that: in step (5), the 15-5PH thin plate crude product 1 after solution heat treatment is pickled by a combination of high temperature alkali washing + conventional pickling, specifically: firstly, it is alkali washed in an industrial alkali washing tank mixed with 70%-80% sodium hydroxide and 20%-30% sodium nitrate at 400°C for 10 minutes, and then it is put into a sulfuric acid + sodium nitrate + water mixed pickling tank (acid concentration 28-35%) for pickling to obtain a 15-5PH thin plate crude product 3,

[0128] Through observation, the surface of 15-5PH sheet rough product 3 is rough and pitted, and the surface quality cannot meet the product standard requirements. Fig.11 As shown;

[0129] The 15-5PH thin plate rough product 3 was cold flattened by the same method as step (6) of Example 2 to obtain a 15-5PH thin plate product 3 with a flatness of 21.4 mm / m. The difference between the same plate and the plate could not meet ±0.1 mm. The final macroscopic plate shape was observed to be obviously uneven by naked eye.

[0130] After subsequent degreasing and other factory processes, the product's tensile strength was measured to be 1120 MPa, yield strength was 1070 MPa, and elongation after break (G=50.8 mm) was 4.5%. Although the strength meets the product use standards, the plate shape cannot meet the standard requirements and cannot be used.

[0131] Comparative Example 5

[0132] The same method as in Example 2 is adopted, except that: in step (6), the specific operation of cold flattening the 15-5PH thin plate rough product 1 is: the 15-5PH thin plate rough product 1 is cold flattened using the same rolling speed and rolling force method as in Example 2, the plate shape is measured once after each rolling pass, and the flatness is finally controlled to be below 19.05 mm / m, and the final rolling pass is 25 passes, thereby obtaining a 15-5PH thin plate product 4, the flatness is 12.0 mm / m, and the plate shape is almost flat in macroscopic observation;

[0133] After subsequent degreasing and other factory processes, the product's tensile strength was measured to be 1190Mpa, yield strength was 1210Mpa, and elongation after break (G=50.8mm) was 5.0%. The yield strength far exceeds the usable yield strength range (yield strength ≤1103Mpa) specified in the international standard (AMS5862) for 15-5PH products.

[0134] Comparative Example 6

[0135] The same method as Example 2 is used, except that in step (2), the passivated 15-5PH slab 1 is subjected to a primary water washing, specifically, the 15-5PH slab 1 is only placed in a cold water tank (15°C) and swung and rinsed for 3 minutes to obtain a 15-5PH slab 5 to be cold rolled.

[0136] After the 15-5PH slab 5 is naturally air-dried, a small amount of acid remains on the surface, such as Fig.12 shown.

[0137] Comparative Example 7

[0138] The same method as in Example 2 was adopted, except that the pickling time in step (2) was 90 min, and finally a 15-5PH slab 6 to be cold-rolled was obtained.

[0139] Through observation, the surface of 15-5PH slab 6 is obviously gray-black, and there is overacidity, such as Fig.13 shown.

[0140] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a 15-5PH stainless steel cold-rolled sheet, characterized in that: The method comprises: (1) Softening heat treatment of the slab; (2) pickling and water washing the slab after softening heat treatment, wherein the pickling acid solution is a hydrofluoric acid solution; (3) cold rolling the washed slab; (4) repeating steps (1) to (3) until the size of the slab meets the requirements, thereby obtaining a crude product; (5) subjecting the crude product to a solution heat treatment; (6) pickling and water washing the crude product after the solution heat treatment, wherein the pickling acid solution is a hydrofluoric acid solution; (7) cold treatment of the crude product after pickling; (8) The crude product after cold flat treatment is degreased and finely processed.

2. The method according to claim 1, characterized in that: The 15-5PH stainless steel cold-rolled thin plate is a 15-5PH precipitation hardened stainless steel cold-rolled thin plate with a thickness of 1-4 mm.

3. The method according to claim 1, characterized in that In step (2), the hydrofluoric acid solution is an aqueous solution of hydrofluoric acid and nitric acid, wherein the concentration of the hydrofluoric acid is 3-5% and the concentration of the nitric acid is 24-30%.

4. The method according to claim 1, characterized in that In step (2), the pickling temperature is 20-25°C and the time is 10-60 minutes.

5. The method according to claim 1, characterized in that In step (2), the water washing method is cold water washing + hot water washing.

6. The method according to claim 1, characterized in that In step (4), repeat 1-3 times.

7. The method according to claim 1, characterized in that In step (6), the hydrofluoric acid solution is an aqueous solution of hydrofluoric acid and nitric acid, wherein the concentration of the hydrofluoric acid is 3-5%, and the concentration of the nitric acid is 24-30%; And / or, the pickling temperature is 20-25°C and the time is 10-60 min.

8. The method according to claim 1, characterized in that: In step (6), in step (6), the water washing method is cold water washing + hot water washing.

9. The method according to claim 1, characterized in that: Calculated according to mass percentage, the element composition of the 15-5PH stainless steel includes: C: 0-0.07%, Mn: 0-1.00%, Si: 0-1.00%, P: 0-0.03%, S: 0-0.015%, Cr: 14.00-15.50%, Ni: 3.50-5.50%, Nb: 5C-0.45%, Cu: 2.50-4.50%, Mo: 0-0.50%, and the balance is Fe.

10. A 15-5PH stainless steel cold-rolled sheet, characterized in that: The thin plate is prepared by the method according to any one of claims 1 to 9.

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