15-5ph stainless steel cold-rolled sheet and method of making

Abstract

This invention relates to a 15-5PH stainless steel cold-rolled sheet and its preparation method, belonging to the technical field of precipitation-hardening stainless steel sheet. It solves the problem that the performance and sheet shape of 15-5PH stainless steel cold-rolled sheets obtained by conventional preparation methods do not meet requirements. The method includes pickling and washing the softened heat-treated slab with hydrofluoric acid solution, cold rolling, solution heat treatment, pickling and washing with hydrofluoric acid solution again, and cold leveling. The pickling of this invention can be carried out at low temperatures, ensuring complete removal of oxide impurities from the sheet surface without causing microstructural changes. The water washing operation after pickling effectively cleans the hydrofluoric acid solution, preventing the formation of new oxide impurities and ensuring the flatness of the sheet after subsequent high-precision rolling and cold leveling. This solves the problem of poor precision in 15-5PH sheets affecting practical applications.

Description

Technical Field

[0001] This invention relates to the field of stainless steel sheet technology, and more particularly to a 15-5PH stainless steel cold-rolled sheet and its preparation method. Background Technology

[0002] 15-5PH material belongs to 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 a key component raw material for large aircraft, and has extremely high requirements for performance and plate shape.

[0003] However, in the current process of preparing 15-5PH thin plates using stainless steel sheet manufacturing technology, due to the high strength and high hardness of this stainless steel, waviness and warping are prone to occur during cold rolling, and cracking may occur in severe cases. Moreover, the pickling process before cold rolling is also very important. The traditional combination of high-temperature alkaline washing and sulfuric acid pickling to remove the oxide scale on the surface of heat-treated hardened stainless steel, while achieving oxide layer removal, will affect the cold rolling effect of the intermediate billet of thin 15-5PH thin plates, thereby affecting the performance and shape of the final product and exacerbating the defective shape.

[0004] Therefore, there is an urgent need for a new method for preparing 15-5PH stainless steel cold-rolled sheet to ensure that the performance and shape of the sheet meet the requirements and to solve the problem that the poor precision of 15-5PH sheet affects its practical application. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a 15-5PH stainless steel cold-rolled sheet and its preparation method, in order to solve at least one of the problems that the performance and sheet shape of the 15-5PH stainless steel cold-rolled sheet obtained by conventional preparation methods do not meet the requirements.

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

[0007] (1) Soften the slab with heat treatment;

[0008] (2) The slab after softening heat treatment is pickled and washed with water, wherein the pickling acid is hydrofluoric acid;

[0009] (3) The washed slab is cold rolled;

[0010] (4) Repeat steps (1)-(3) until the dimensions of the slab meet the requirements to obtain a rough product;

[0011] (5) Perform solution heat treatment on the crude product;

[0012] (6) The crude product after solution heat treatment is pickled and washed with water, wherein the pickling acid is hydrofluoric acid;

[0013] (7) Perform cold leveling treatment on the crude product after pickling;

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

[0015] Furthermore, the 15-5PH stainless steel cold-rolled sheet is a 15-5PH precipitation-hardening 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 hydrofluoric acid is 3-5% and the concentration of nitric acid is 24-30%.

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

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

[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 hydrofluoric acid is 3-5% and the concentration of nitric acid is 24-30%.

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

[0022] Furthermore, based on mass percentage calculations, the elemental 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%, with the balance being Fe.

[0023] On the other hand, embodiments of the present invention provide a 15-5PH stainless steel cold-rolled sheet, which is obtained 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 traditional high-temperature alkaline washing and / or acid washing methods can lead to high-temperature microstructure evolution, incomplete cleaning, or acid residue, which can affect the precision of subsequent cold rolling of thin plate intermediate billets or subsequent cold flattening of finished products, ultimately affecting product performance and plate shape. The present invention uses hydrofluoric acid solution for acid washing and a water washing step after acid washing, which can overcome the above problems and achieve high-precision preparation of 15-5PH precipitation hardening stainless steel thin plates.

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

[0027] 2. This invention achieves thorough removal of oxidative impurities and other contaminants from the surface of thin plates at 15-5 pH by controlling the concentration and ratio of hydrofluoric acid and nitric acid in the hydrofluoric acid pickling solution at low temperature, and avoids excessive corrosion of the thin plate surface. In the subsequent cold rolling or cold flattening process, it ensures that there are no defects in plate shape such as large bending or warping, or changes in internal structure.

[0028] 3. By controlling the temperature and time of hydrofluoric acid pickling, this invention can thoroughly remove oxidized impurities and other contaminants from the surface of thin plates at pH 15-5, while avoiding over-oxidation, over-acidity, and incomplete acid cleaning during the pickling process, thus ensuring the surface quality of the pickled products.

[0029] 4. This invention employs a two-stage water washing method to remove residual hydrofluoric acid pickling solution from the surface of thin plates at pH 15-5 after pickling. Cold water rinsing removes oxides that cannot be naturally detached after pickling and a small amount of adhering residual acid, while hot water rinsing removes the residual acid. This two-stage water washing method, combining cold and hot water rinsing, avoids the formation of new oxide layers due to residual hydrofluoric acid pickling solution after pickling, thereby improving the effect of subsequent cold rolling or cold flattening treatments and enhancing the precision of thin plate products.

[0030] 5. The present invention utilizes hydrofluoric acid solution to pickle 15-5PH thin plates after heat treatment, which can be carried out at low temperatures, far below the microstructure transformation temperature of 15-5PH stainless steel (≥480℃). This allows for the complete removal of oxide impurities from the surface of the thin plate while ensuring its performance. The water washing operation after pickling cleans the hydrofluoric acid solution, preventing the formation of new oxide impurities, which is beneficial for subsequent high-precision rolling and cold leveling. This ensures the flatness of the 15-5PH stainless steel thin plate, thus solving the problem of poor precision of thin plates affecting practical applications.

[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 rough product before cold leveling can also be pickled using the pickling solution and pickling process, which simplifies the process and facilitates the subsequent waste liquid treatment.

[0032] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0033] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0034] Figure 1 This is an appearance view of 15-5PH slab A-1 after being pickled with hydrofluoric acid solution in Example 1;

[0035] Figure 2 This is an appearance diagram of 15-5PH slab A-2 after being pickled with hydrofluoric acid solution in Comparative Example 1.

[0036] Figure 3 This is an appearance diagram of 15-5PH slab A-3 after being pickled with hydrofluoric acid solution in Comparative Example 2.

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

[0038] Figure 5 This is a drawing showing the appearance and shape of the 15-5PH thin sheet rough product 1 after cold rolling in Example 2;

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

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

[0041] Figure 8 This is an appearance diagram of 15-5PH slab 2 treated with the traditional high-temperature alkaline washing + acid washing combination method in Comparative Example 3;

[0042] Figure 9 This is an appearance diagram of the 15-5PH thin sheet rough product 2 after cold rolling, as shown in Comparative Example 3;

[0043] Figure 10 The sheet shape diagram of the rough product 2 of the 15-5PH thin sheet after cold rolling in Comparative Example 3 is shown.

[0044] Figure 11 This is an appearance image of the 15-5pH thin plate rough product 3 treated by the traditional high-temperature alkaline washing + acid washing combination method in Comparative Example 4.

[0045] Figure 12 This is an appearance diagram of the 15-5PH slab 5 of Comparative Example 6 after being pickled with hydrofluoric acid solution.

[0046] Figure 13 The image shows the appearance of 15-5PH slab 6 after being pickled with hydrofluoric acid solution in Comparative Example 7. Detailed Implementation

[0047] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which 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 intended to limit the scope of the present invention.

[0048] In the current process of preparing 15-5PH stainless steel sheets using existing stainless steel sheet manufacturing techniques, the high strength and hardness of this stainless steel make it prone to waviness and warping during cold rolling, which can lead to cracking in severe cases. Furthermore, the pre-rolling pickling process is also crucial. The traditional combination of high-temperature alkaline washing and sulfuric acid pickling to remove oxide scale from heat-treated hardened stainless steel, while achieving oxide layer removal, can negatively impact the cold rolling effect of the thin-thickness 15-5PH sheet intermediate billet. This results in the cold-rolled sheet exhibiting slight bulging, waviness, and other poor shape, thus affecting the final product's performance and shape, and exacerbating the shape defects.

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

[0050] (1) Soften the slab with heat treatment;

[0051] (2) The slab after softening heat treatment is pickled and washed with water, wherein the pickling acid is hydrofluoric acid;

[0052] (3) The washed slab is cold rolled;

[0053] (4) Repeat steps (1)-(3) until the dimensions of the slab meet the requirements to obtain a rough product;

[0054] (5) Perform solution heat treatment on the crude product;

[0055] (6) The crude product after solution heat treatment is pickled and washed with water, wherein the pickling acid is hydrofluoric acid;

[0056] (7) Perform cold leveling treatment on the crude product after pickling;

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

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

[0059] It should be noted that the softening heat treatment can be a solution heat treatment, annealing heat treatment, or other heat treatment methods.

[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 hours.

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

[0062] The inventors discovered during the preparation of 15-5PH stainless steel sheets that, when using traditional high-temperature alkaline washing methods to remove surface oxides and contaminants, the 15-5PH stainless steel sheets undergo uncontrollable microstructural evolution due to excessively high temperatures, thus affecting the performance and shape of the final product. Traditional pickling methods using inorganic acids such as hydrochloric acid and sulfuric acid often suffer from problems such as incomplete cleaning after multiple pickling cycles, acid residue leading to the formation of new oxide layers, high cost, and low efficiency, affecting the subsequent cold rolling effect of achieving a flat 15-5PH sheet shape. Therefore, this invention uses hydrofluoric acid to pickle the heat-treated slab.

[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%, or 5%; the concentration of nitric acid is 24-30%, which can be 24%, 25%, 26%, 27%, 28%, or 29%; and 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, or 5:7, in order to achieve thorough removal of oxidized impurities and other contaminants from the surface of the 15-5 pH thin plate at low temperature, and to ensure that there are no large bends, warps, or other plate shape defects or internal defects. Phenomena such as changes in fabric morphology can occur. If the concentration of hydrofluoric acid / nitric acid is too high, it will lead to excessive corrosion of the thin plate surface, affecting 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, it will lead to a decrease in pickling ability, uneven pickling, affecting the surface quality of the product and subsequent processing, and prolonging the pickling time. If the proportion of hydrofluoric acid is too high, an over-acid reaction will occur, the pickling reaction will be too violent and sensitive to temperature and time, resulting in an uncontrolled pickling process. If the proportion of nitric acid is too high, it will lead to uneven subsequent passivation reaction and affect the uniformity of the product surface color.

[0065] Furthermore, in step (2), the pickling temperature range is 20-25℃. Unlike the traditional high-temperature alkaline washing method, the present invention uses hydrofluoric acid solution to remove oxidized impurities and other pollutants from the surface of 15-5PH stainless steel sheet at a lower 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 pickling temperature for 15-5PH stainless steel sheets using hydrofluoric acid solution is 20°C.

[0067] Furthermore, in step (2), the pickling time using hydrofluoric acid solution is 10-60 minutes. If the time is too long, it will lead to over-acid reaction and macroscopic phenomena such as waves and bulges, resulting in poor plate shape. If the time is too short, it will lead to uneven removal of the surface oxide layer, affecting subsequent rolling, cold leveling 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 min, 30 min, 40 min, and 60 min, 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 rinsing and hot water rinsing, to avoid the formation of a new oxide layer due to the residue of hydrofluoric acid pickling solution after pickling, thereby improving the effect of subsequent cold rolling or cold flattening treatment and improving the precision of the thin plate product.

[0070] It should be noted that the present invention uses a method of immersing the entire plate in a water tank and oscillating it to complete the water washing. Cold water (10-25℃) is used to rinse away the oxides that cannot be naturally removed after pickling and a small amount of residual acid. Hot water (>70℃) is used to rinse away the residual acid. Only by combining cold water rinsing with hot water rinsing can a smooth surface be achieved without black oxides or acid residue.

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

[0072] The inventors discovered in their research that, due to the high strength and hardness of 15-5PH precipitation-hardening stainless steel, it is prone to waviness and warping during cold rolling, and in severe cases, cracking may occur. Furthermore, the heat treatment after cold rolling has a significant impact on the sheet shape, exacerbating the problem of poor sheet shape. The small thickness of 15-5PH thin plates (<4mm) increases the difficulty of rolling, making the sheet deformation after heat treatment more severe, and increasing the difficulty of controlling performance and sheet shape. Moreover, the high-temperature microstructure evolution caused by traditional high-temperature alkaline washing and / or pickling methods, or incomplete cleaning or acid residue, has a greater impact on the subsequent cold rolling treatment of thin-thickness intermediate billets or the subsequent cold leveling treatment of finished products.

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

[0074] According to a preferred embodiment, the thickness of the thin plate is 4 mm, 2.8 mm, 1.8 mm, and 1.27 mm, respectively.

[0075] Specifically, in step (3), in order to achieve the expected performance and dimensional accuracy of the final product, the present invention requires cold rolling of 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 multi-stage 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)-(3) are repeated until the dimensions of the slab meet the requirements, and a rough product is obtained.

[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 segments is 1-3 times, that is, the total rolling stroke is ≤3 segments of cold rolling.

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

[0081] Specifically, in step (3), the reduction amount of each cold rolling pass is reduced successively according to the pass, with a maximum of 0.5 mm.

[0082] It should be noted that 15-5PH sheet metal, as a raw material for key components of large aircraft, is required to be delivered in a solution-treated state, and therefore must undergo solution heat treatment.

[0083] Specifically, in step (5), the present invention performs solution heat treatment on the cold-rolled rough product, wherein the solution heat treatment temperature is 1040℃ and the time is 20min.

[0084] It should be noted that thin sheets with a thickness of 15-5PH are highly sensitive to internal stress and are prone to bending. Therefore, solution heat treatment of the rough finished product can easily cause bending, making it unable to meet delivery requirements. Thus, a cold leveling process is added to straighten the sheet after solution heat treatment. Furthermore, to remove oxide impurities generated on the surface of the sheet product during solution heat treatment and improve the surface quality and shape of the finished product, the cold-rolled rough finished product needs to be pickled and cleaned before undergoing cold leveling.

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

[0086] It should be noted that the process of using hydrofluoric acid solution to pickle and wash the crude product after solid solution heat treatment in step (6) is the same as the process of pickling and washing the crude product after 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 hydrofluoric acid is 3-5% and the concentration of nitric acid is 24-30%.

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

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

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

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

[0092] Specifically, in order to make the surface of the thin plate cleaner and more aesthetically pleasing, 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 as follows: passivation is performed using 22-28% sulfuric acid, the temperature is controlled between 45℃ and 65℃, and the passivation time does not exceed 2 minutes.

[0093] It should be noted that the cold flattening and straightening process is the final step in product manufacturing and sheet shape control. Lubricating oil is required to ensure that no additional scratches or other impurities are generated during the cold flattening process, thus ensuring the surface quality of the product. Therefore, after the thin sheet product is cold flattened, it is also necessary to degrease the product to improve the surface quality of the finished product, and then perform finishing processes after degreasing, including grinding and shearing.

[0094] The inventors discovered, while adjusting the manufacturing process of 15-5PH stainless steel sheets, that replacing the pickling process entirely with hydrofluoric acid pickling greatly benefits subsequent secondary (or tertiary) cold rolling and cold leveling processes. Hydrofluoric acid pickling does not alter the internal structure and effectively removes surface impurities. Therefore, after a second cold rolling process following hydrofluoric acid pickling, the sheet shape remains essentially straight with no noticeable waviness on the surface. Even if the sheet exhibits bending due to uneven heating during solution heat treatment and unavoidable residual stress within the sheet, the subsequent cold leveling process allows for easy straightening of the sheet by controlling the number of cold leveling passes and the amount of cold leveling, achieving the required straightness and meeting product performance requirements.

[0095] Specifically, based on mass percentage, the elemental composition of the 15-5PH stainless steel of this 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%, with the balance being Fe.

[0096] According to a preferred embodiment of the present invention, the elements constituting the 15-5PH stainless steel, calculated by mass percentage, include: C 0.042%, Mn 0.43%, Si 0.41%, P 0.022%, S 0.0013%, Cr 15.15%, Ni 4.05%, Nb 0.31%, Cu 3.31%, Mo 0.080%, with the balance being F; or the elements constituting 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%, with the balance being Fe.

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

[0098] Specifically, the elemental composition of the 15-5PH stainless steel sheet, calculated by mass percentage, 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%, with the balance being Fe; the performance indicators of the 15-5PH stainless steel sheet are: tensile strength ≤1276 MPa, yield strength ≤1103 MPa, elongation after fracture (G=50.8 mm) ≥3%, and straightness ≤19.05 mm / m.

[0099] The technical solution of the present invention will be further explained below with reference to specific embodiments.

[0100] Example 1

[0101] (1) At a temperature of 20°C, the 15-5PH slab A, which has been cooled to room temperature after annealing heat treatment, is pickled using hydrofluoric acid solution. The pickling method is immersion. The hydrofluoric acid solution includes 4% HF and 28% HNO3. According to the mass percentage, the chemical composition of the 15-5PH slab A used in this embodiment includes: C 0.042%, Mn 0.43%, Si 0.41%, P 0.022%, S 0.0013%, Cr 15.15%, Ni 4.05%, Nb 0.31%, Cu 3.31%, Mo 0.080%, with the balance being Fe. The slab size is 30×200mm and the thickness is 3.18mm.

[0102] (2) At 45℃, the thin plate is passivated for 2 minutes using a 20% sulfuric acid solution. The passivated thin plate is then subjected to a two-stage water wash: first, it is placed in a cold water tank (15℃) and rinsed for 3 minutes, and then placed in a hot water tank (75℃) and rinsed for 3 minutes to obtain the pickled 15-5PH plate blank A-1.

[0103] During the experiment, after 6 minutes of pickling in step (1), the oxide scale on the surface of the thin plate could be clearly observed to peel off, such as Figure 1 As shown in (a); after soaking for another 10 minutes, the thin plate is removed and rinsed with cold water as in step (2). It can be seen that the oxide scale on the surface of the thin plate 1 has been completely removed, as shown in (a). Figure 1 As shown in (b).

[0104] Comparative Example 1

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

[0106] During the experiment, after 10 minutes of acid washing in step (1), the thin plate was removed, and obvious oxidation marks could be observed, such as... Figure 2 As shown in (a); after being immersed in acid solution again for pickling, the oxide spots can be washed away, but after rinsing with cold water in step (2), the surface of the thin plate 2 still shows signs of incomplete acid removal, such as... Figure 2 As shown in (b).

[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 the pickled 15-5PH slab A-3 was obtained.

[0109] During the experiment, after 10 minutes of pickling in step (1), it was clearly observed that the oxide scale on the surface of the thin plate was not completely removed, such as... Figure 3 As shown in (a), it takes at least 40 minutes to achieve a state where the oxide layer is basically removed; however, after rinsing with cold water in step (2), it is still obvious that the black oxide scale that has not been completely removed is still attached to the surface of the thin plate 3, such as Figure 3 As shown in (b).

[0110] Example 2

[0111] (1) The 15-5PH slab 1 was annealed at 600℃ for 10h; the chemical composition of the 15-5PH slab 1, calculated by mass percentage, 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%, with the balance being Fe; the plate 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) Cool the annealed slab to room temperature and place the annealed heat-treated and cooled 15-5PH slab 1 into the pickling tank for pickling. The mixed pickling solution includes 4% HF and 28% HNO3. Pickling is carried out at 20°C. In the initial stage, obvious yellow smoke is observed to be produced, accompanied by a large number of bubbles, and the reaction is vigorous. After about 10 minutes, the bubbles and smoke decrease. After about 20 minutes, only a small number of bubbles are produced, and the degree of reaction is significantly reduced. Continue pickling for 40 minutes and take it out.

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

[0114] The passivated sheet is subjected to a two-stage water washing process: first, it is placed in a cold water tank (15℃) and rinsed for 3 minutes by agitation, and then placed in a hot water tank (75℃) and rinsed for 3 minutes by agitation, to obtain the 15-5PH slab 1 to be cold rolled;

[0115] Upon observation, the oxide layer on the surface of the 15-5PH slab 1 to be cold-rolled was completely removed, revealing a light grayish-white color. Figure 4 As shown, there is no acid residue on the surface, which meets the requirements for product surface quality.

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

[0117] (4) The crude product 1 of 15-5PH thin plate was subjected to solution heat treatment at 1040℃ for 20 min;

[0118] (5) The crude 15-5PH thin plate product 1 after solution heat treatment is acid-washed using the same method as in step (2) to obtain the crude 15-5PH thin plate product 1, as follows: 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 was completely removed, and the surface was bright metallic. Except for the scratches caused by unavoidable manual handling during the factory process, there were no acid residues, oxides or other impurities on the surface, which met the requirements for product surface quality.

[0120] (6) The 15-5PH thin plate rough product 1 obtained in step (5) is subjected to cold leveling treatment. The specific operation is as follows: control the roll speed to 0.8 m / s, the rolling force to 1200 tons, and the rolling passes to 7. The final cold leveling amount is not higher than 0.05 mm, resulting in 15-5PH thin plate product 1 with a flatness of 8.0 mm / m. Visual observation shows that the final macroscopic plate shape has almost no bending, warping, or other plate shape defects. Figure 7 As shown;

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

[0122] Comparative Example 3

[0123] The same method as in Example 2 was used, except that in step (2), after the annealed 15-5PH slab 1 was cooled to room temperature, the slab 1 was cleaned by high-temperature alkaline washing + traditional acid washing. Specifically, the slab 1 was first alkaline washed for 10 minutes in an industrial alkaline washing tank containing 70%-80% sodium hydroxide and 20%-30% sodium nitrate at 400℃, and then placed in an acid washing tank containing sulfuric acid + sodium nitrate + water (acid concentration 28-35%) to be acid washed, and finally the 15-5PH slab 2 to be cold rolled was obtained.

[0124] Upon observation, obvious bulges appeared on the surface of the 15-5PH slab 2, such as... Figure 8 As shown.

[0125] Step (3) uses the same cold rolling process as in step (3) of Example 2 to cold roll the 15-5PH slab 2, obtaining a 15-5PH thin sheet rough product 2 with a thickness of 1.33 mm; obvious scratches due to over-shaping can be observed on the surface of the 15-5PH thin sheet rough product 2 with the naked eye, such as Figure 9 As shown, when viewed from the side, the plate exhibits a distinctly large curvature, such as... Figure 10 As shown.

[0126] Comparative Example 4

[0127] The same method as in Example 2 was used, except that in step (5), a combination of high-temperature alkaline washing and traditional acid washing was used to acid wash the crude 15-5PH thin plate after solution heat treatment. Specifically, the product was first alkaline washed for 10 minutes in an industrial alkaline washing tank containing 70%-80% sodium hydroxide and 20%-30% sodium nitrate at 400℃, and then placed in an acid washing tank containing sulfuric acid, sodium nitrate and water (acid concentration 28-35%) to obtain the crude 15-5PH thin plate product 3.

[0128] Observation revealed that the surface of the 15-5PH thin sheet rough product 3 was rough, forming a pitted surface, and the surface quality failed to meet the product standard requirements. Figure 11 As shown;

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

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

[0131] Comparative Example 5

[0132] The same method as in Example 2 was used, except that in step (6), the specific operation of cold flattening the 15-5PH thin plate rough product 1 was as follows: the same roll speed and rolling force method as in Example 2 was used to cold flatten the 15-5PH thin plate rough product 1. The plate shape was measured once for each rolling pass, and the flatness was finally controlled below 19.05 mm / m. The final rolling pass was 25 passes, and the 15-5PH thin plate product 4 was obtained with a flatness of 12.0 mm / m. The plate shape was almost a flat plate shape when observed macroscopically.

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

[0134] Comparative Example 6

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

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

[0137] Comparative Example 7

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

[0139] Upon observation, the surface of 15-5PH slab 6 clearly showed a grayish-black color, indicating over-acidification. Figure 13 As shown.

[0140] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing 15-5PH stainless steel cold-rolled sheet, characterized in that, The method includes: (1) The slab is subjected to softening heat treatment; (2) The slab after softening heat treatment is pickled and washed with water, wherein the pickling acid is hydrofluoric acid; (3) The washed slab is cold rolled; (4) Repeat steps (1)-(3) until the dimensions of the slab meet the requirements to obtain a rough product; (5) The crude product is subjected to solution heat treatment; (6) The crude product after solution heat treatment is pickled and washed with water, wherein the pickling acid is hydrofluoric acid; (7) The crude product after pickling is subjected to cold leveling treatment, wherein lubricating oil is used in the cold leveling treatment; (8) The crude product after cold leveling is degreased and then finely processed; The elemental composition of the 15-5PH stainless steel, calculated by mass percentage, 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%, with the balance being Fe; In steps (2) and (6), the hydrofluoric acid solution is an aqueous solution of hydrofluoric acid and nitric acid, wherein the concentration of hydrofluoric acid is 3-5% and the concentration of nitric acid is 24-30%; In steps (2) and (6), the pickling temperature is 20-25℃ and the time is 10-60 min; In steps (2) and (6), the washing method is cold water rinsing + hot water rinsing.

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

3. The method according to claim 1, characterized in that, The concentration of the hydrofluoric acid is 3.5-4.5%, and the concentration of the nitric acid is 26-28%.

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

5. A 15-5PH stainless steel cold-rolled sheet, characterized in that, The thin plate is prepared by the method described in any one of claims 1-4.

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