Austenitic stainless steel whole-hydrochloric-acid-based stepped pickling method

Abstract

The invention belongs to the field of stainless steel pickling, and particularly relates to an austenitic stainless steel whole-hydrochloric-acid-based stepped pickling method. At present, stainless steel pickling is mainly based on a mixed acid pickling (nitric acid and hydrofluoric acid) system, the problem of three-waste discharge exists in the pickling process, the pickling process is only suitable for removing ferritic stainless steel with weak binding force between an oxide layer and a metal matrix through pickling, and the oxide layers on the surfaces of ferritic cold plate stainless steel and austenitic stainless steel are difficult to remove. In order to solve the problems, hydrochloric acid is used for providing an acid environment, a pre-pickling and grading final pickling cooperative treatment method is adopted, a compact oxide layer on the surface of the austenitic stainless steel can be effectively removed, surface polishing and surface passivation can be achieved through the anodic polarization effect, and the stainless steel surface after pickling is free of pitting corrosion and intergranular corrosion phenomena; and the pickled stainless steel surface has high smoothness, the leveling and polishing quality of the BA plate can be remarkably improved, meanwhile, the production cost is low, and pickling waste liquid can be regenerated and recycled.

Description

Technical Field

[0001] The invention belongs to the field of stainless steel pickling, and in particular relates to a full hydrochloric acid-based step pickling method for austenitic stainless steel. Background Art

[0002] As the output of stainless steel increases year by year, the quality requirements for products are becoming more and more stringent. Among them, surface quality is a key indicator for evaluating the quality of stainless steel plate and strip products. Its quality is directly affected by the rationality of the heat treatment process and the subsequent pickling process. At the same time, with the improvement of stainless steel surface quality, cost and environmental issues are becoming increasingly prominent. At present, domestic and foreign stainless steel companies generally use hydrofluoric acid-nitric acid mixed acid process for final pickling. However, this process has significant defects. The reduction product NO produced by nitric acid x Gas and nitrite solution will pollute the environment. In addition, the mixed acid pickling process is relatively weak in pickling ability, and it is difficult to remove the chromium-poor layer on the surface of stainless steel, which leads to the problem of spots on the surface of stainless steel during cold rolling and heat treatment after pickling, affecting the surface quality of stainless steel. The existence of these problems not only makes it very difficult to directly produce high-quality products, but also requires mechanical and chemical polishing treatment to solve them in the later stage, which will also lead to a significant increase in production costs.

[0003] Patent CN115896794A discloses a stainless steel pickling system and its pickling process, which includes two pickling solutions A and B, wherein pickling solution A is sulfuric acid and nitric acid, with sulfuric acid as the main acid and nitric acid as the auxiliary acid. Pickling solution B is a mixed solution of nitric acid and hydrofluoric acid, with nitric acid as the main acid and hydrofluoric acid as the auxiliary acid, and bright white stainless steel is obtained through a staged pickling design. Patent CN114150124B discloses "a method for annealing and pickling of high nickel-chromium stainless steel cold-rolled strip", which is divided into three steps: cold rolling annealing (1120-1140℃; holding time 1.0-2.0min / mm), electrolytic pickling and mixed acid pickling (HF concentration is 25-35g / l, HNO3 concentration is 100-120g / l, temperature is 55-60℃).

[0004] Patent CN115287419B discloses an annealing and pickling process for high-temperature resistant austenitic stainless steel cold-rolled strip. The process is divided into three steps: cold rolling annealing, electrolytic pickling and mixed acid pickling. Step 1: cold rolling annealing: the annealing temperature is 1120±10℃, the effective length of the annealing furnace in the high temperature section is 60m, according to the principle of 1-1.5min / mm insulation of the steel plate in the high temperature section, the strip passing speed is calculated according to the effective length of the furnace in the high temperature section and the thickness of the strip; Step 2: electrolytic pickling: the first section pickling medium is Na2SO4; the specific gravity is 1.20-1.30g / cm -3, electrolysis temperature 75±5℃, electrolysis current 2000-7000A; the second pickling medium HNO3, acid concentration 70-140g / L, temperature 50±5℃, electrolysis current 2000-5000A; step three: mixed acid pickling: HF and HNO3 are mixed, HNO3 concentration is 120-250g / L, HF concentration is 15-30g / L, Fe~(n+)≤40g / L, mixed acid temperature is 45~55℃.

[0005] The above patents are all based on a mixed acid pickling (nitric acid + hydrofluoric acid) system. There are three waste discharge problems during the pickling process, such as nitrogen oxide emissions, nitrite waste liquid disposal and heavy metal hazardous waste disposal. These common problems in the stainless steel pickling industry directly affect the green development of the stainless steel industry.

[0006] Patent CN202210676982 discloses a method for removing oxide scale from ferritic stainless steel. After rolling, the ferritic stainless steel strip is uncoiled and straightened, and then shot peened to remove loose oxide scale on the surface of the steel plate. After shot peening, the strip is sprayed; the strip after spraying is pickled with a hydrochloric acid pickling solution, rinsed and dried after pickling; the applicable ferritic stainless steel composition is C: 0.01-0.15wt%, Si: 0.4-1wt%, Mn: 0.04-1.25wt%, P: 0.03-0.04wt%, S: 0.02-0.03wt%, Ni: 0-0.6wt%, Cr: 12-32wt%, Mo: 0-1.3wt%, N: 0-0.015wt%, Al: 0-0.3wt%.

[0007] The above hydrochloric acid pickling method is only aimed at removing the oxide layer on the surface of ferritic hot-rolled stainless steel plates. Since ferritic stainless steel does not contain nickel, the oxide layer on the surface of ferritic stainless steel contains only iron and chromium spinel phases. The oxide layer on the surface of hot-rolled stainless steel plates is relatively brittle, and this oxide layer is relatively weakly attached to the substrate. It is very easy to be basically removed from the stainless steel substrate during the dephosphorization and shot peening process. The residual oxide layer on the surface of stainless steel after dephosphorization and shot peening belongs to the type of stainless steel that is easy to pickle. However, austenitic stainless steel belongs to the type of nickel-containing steel. The surface oxide layer contains spinel phases such as iron, chromium, and nickel. Because the oxide layer contains nickel, it not only makes the surface oxide layer denser, but also has a stronger ability to adhere to the substrate. The surface oxide layer is relatively weak in brittleness and has a relatively large toughness. It is extremely difficult to basically remove the surface oxide layer through dephosphorization and shot peening like ferritic stainless steel, and it has a strong inhibitory effect on the penetration and electrochemical reaction of the pickling solution. Moreover, if the pickling of austenitic stainless steel is not properly controlled, it is very easy to produce over-pickling phenomena, such as surface micropores, pitting, etc., which greatly affect the surface quality. Summary of the invention

[0008] In view of the above problems, the present invention provides a method for full hydrochloric acid-based step pickling of austenitic stainless steel. The method is mainly for hard-to-clean stainless steel such as 304, 316 and other austenitic stainless steels. After hot rolling and shot peening, the above austenitic stainless steel will form a dense oxide layer containing chromium, nickel, etc. on its surface, and it is difficult to remove the surface oxide layer by ordinary pickling, mixed acid pickling and conventional hydrochloric acid pickling methods.

[0009] The austenitic stainless steel all-hydrochloric acid-based step pickling method of the present invention is carried out according to the following steps: The austenitic stainless steel after hot rolling and shot peening is directly subjected to full hydrochloric acid-based cascade pickling; the full hydrochloric acid-based cascade pickling process is divided into S1-pre-pickling operation and final pickling operation; S1-Pre-pickling operation: Pre-pickling operation is performed using a pre-pickling solution, which mainly includes hydrochloric acid and a promoter additive, and the promoter additive includes one of PBTCA (2-phosphonobutane-1,2,4-tricarboxylic acid), benzotriazole, and ethylenediaminetetramethylenephosphonic acid; The mass concentration of hydrochloric acid in the pre-pickling solution is 10%~31%, and the mass concentration of the promoting additive is 0.1%~1%; When the mass concentration of hydrochloric acid in the pre-pickling solution is ≥28%, a stabilizing additive needs to be added; the stabilizing additive includes one of dihydroxybenzoic acid, p-hydroxybenzoic acid, and acetoethoxyaniline, and the mass concentration in the pre-pickling solution is 0.3%~2%; The pickling temperature of the pre-pickling operation is 40℃~80℃, and the time is 20s~70s.

[0010] A final pickling solution is used for final pickling operation, wherein the final pickling solution mainly comprises hydrochloric acid, hydrogen peroxide, ferric chloride and a stabilizing additive, wherein the stabilizing additive comprises one of dihydroxybenzoic acid, p-hydroxybenzoic acid and acetoethoxyaniline; The final pickling operation includes: S2-1 level final pickling operation, S3-2 level final pickling operation, S4-3 level final pickling passivation operation; S2-1 level final pickling operation: Use 1 level final pickling solution for 1 level final pickling operation. The mass concentration of each substance in the 1 level final pickling solution is as follows: hydrochloric acid 5%~25%, hydrogen peroxide 0.5%~3%, ferric chloride 4%~10%, stabilizing additive 0.3%~2%; The temperature of the first-level final pickling is 20℃~70℃, and the time is 20s~70s.

[0011] S3-2-level final pickling operation: Use 2-level final pickling solution for 2-level final pickling operation. The mass concentration of each substance in the 2-level final pickling solution is as follows: hydrochloric acid 5%~25%, hydrogen peroxide 0.5%~3%, ferric chloride 4%~10%, stabilizing additive 0.3%~2%; The temperature of the second-level final pickling is 20℃~70℃, and the time is 20s~70s.

[0012] S4-3-level final pickling and passivation operation: Use 3-level final pickling solution for 3-level final pickling operation. The mass concentration of each substance in the 3-level final pickling solution is as follows: hydrochloric acid 0.5%~3%, hydrogen peroxide 2%~6%, stabilizing additive 0.1%~0.5%, and no ferric chloride is added to the 3-level final pickling solution; The temperature of the final pickling of level 3 is 20℃~50℃, and the time is 20s~70s.

[0013] Compared with the prior art, the invention has the advantages that after multiple pickling, the surface finish of the stainless steel is high, no oxide layer remains, the cost of pickling is greatly reduced, and the efficiency of pickling is improved. At the same time, as the number of final pickling increases, the flatness of the stainless steel sample is greatly increased, and the step pickling avoids the occurrence of micropores and pitting caused by excessive pickling at one time.

[0014] The beneficial effects of the present invention are as follows: 1. The stainless steel all-hydrochloric acid-based step pickling method provided by the present invention uses hydrochloric acid as the main component of the pickling solution, which can not only effectively avoid the pickling waste liquid pollution and pickling sludge problems, but also the hydrochloric acid acid waste liquid can be regenerated and recycled. At the same time, step-by-step pickling helps to avoid micropores or pitting on the stainless steel surface, and helps to improve the surface quality of the stainless steel.

[0015] 2. The present invention utilizes a step-by-step final pickling method to destroy the continuous phase oxide layer on the surface of stainless steel with the aid of a hydrochloric acid-based pre-pickling solution, and then in a high-acid, low-oxidant environment and the electrochemical effect of chloride ions, the oxide layer on the surface of the stainless steel is stripped, the chromium-depleted layer is dissolved, and the surface is electrochemically polished through the numerous micro-region galvanic cell effects formed by crevice corrosion, thereby achieving the removal of the oxide layer and the chromium-depleted layer on the surface of the stainless steel and improving the surface flatness.

[0016] The present invention develops a new hydrochloric acid-based step pickling process for stainless steel by analyzing the surface oxide layer of stainless steel after hot rolling and shot peening, namely: first, under relatively high acidic conditions, by virtue of the small radius of chloride ions and the strong ability to penetrate oxides, the continuous phase structure of the surface oxide layer of stainless steel is destroyed by the hydrochloric acid-based system, so that the surface oxide layer of stainless steel is transformed from a dense continuous structure to a porous non-continuous structure, and better electrochemical stripping conditions of the surface oxide layer are created for the micro-region galvanic cell crevice corrosion effect of the final pickling. Then, an appropriate amount of hydrogen peroxide is added to a moderate hydrochloric acid concentration, and the electrochemical reaction behavior of the austenitic stainless steel surface in the final pickling system is controlled by controlling the redox potential of the hydrochloric acid-based system, which not only accelerates the stripping effect of the surface oxide layer, but also forms an electrochemical polishing effect on the stainless steel surface, thereby improving the surface quality of the stainless steel, and finally achieving the passivation of the austenitic stainless steel surface under the hydrochloric acid pickling system, further improving the corrosion resistance of the austenitic stainless steel surface. The present invention not only optimizes the current clean production status of stainless steel pickling, but also has low production cost and good stainless steel surface quality, and can make the stainless steel pickling process truly realize a green, environmentally friendly, recyclable new high-efficiency pickling technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a 3D comparison diagram of the microscopic surface of the stainless steel before pickling in Example 2 of the present invention.

[0018] Figure 2 This is a 3D comparison diagram of the microscopic surface of the stainless steel after pickling in Example 2 of the present invention. DETAILED DESCRIPTION

[0019] The technical scheme of the present invention is clearly and completely described below in conjunction with the embodiments and the accompanying drawings. It should be pointed out that the embodiments described in the present invention are only used to further explain and illustrate, rather than to limit the scope of application. Based on the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0020] The raw material used in the present invention is a hot-rolled shot-peened stainless steel plate from a domestic steel plant.

[0021] The hydrochloric acid, PBTCA, benzotriazole, ethylenediaminetetra(methylenephosphonic acid) and the like used in the present invention are all commercially available products.

[0022] The present invention adds a promoting additive and a stabilizing additive during the pre-pickling operation and the final pickling operation respectively, so no irritating gas is generated during the entire hydrochloric acid-based cascade pickling process.

[0023] Example 1: 304 austenitic stainless steel S1-Pre-pickling operation: The main substances and their mass fractions in the pre-pickling solution in the pre-pickling tank are as follows: 25% hydrochloric acid and 1% PBTCA; the stainless steel sample to be pickled is immersed in the pre-pickling solution for pre-pickling, the pickling temperature is 70°C, the pickling residence time is 70 seconds, the stainless steel sample after pickling is washed with water at room temperature, and brushed with a brushing machine for 5 seconds; the pre-pickled stainless steel is obtained.

[0024] S2-1 level final pickling operation: the main substances and their mass fractions in the 1 level final pickling solution in the 1 level final pickling tank are as follows: 15% hydrochloric acid, 4% ferric chloride, 3% hydrogen peroxide and 2% dihydroxybenzoic acid as a stabilizing additive; the pre-pickled stainless steel is immersed in the 1 level final pickling solution for 1 level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, the pickled sample is washed with water at room temperature, and scrubbed with a scrubber for 5 seconds; and 1 level final pickled stainless steel is obtained.

[0025] S3-2 level final pickling operation: the main substances and their mass fractions in the level 2 final pickling solution in the level 2 final pickling tank are as follows: 13% hydrochloric acid, 6% ferric chloride, 2% hydrogen peroxide and 1% dihydroxybenzoic acid as a stabilizing additive; immerse the level 1 final pickling stainless steel in the level 2 final pickling solution for level 2 final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain level 2 final pickling stainless steel.

[0026] S4-3-level final pickling and passivation operation: The main substances and their mass fractions in the 3-level final pickling solution in the 3-level final pickling tank are as follows: 3% hydrochloric acid, 6% hydrogen peroxide and 0.5% dihydroxybenzoic acid as a stabilizing additive; immerse the 2-level final pickling stainless steel in the 3-level final pickling solution for 3-level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain 3-level final pickling passivated austenitic stainless steel.

[0027] The surface of the 3-level final pickling passivated austenitic stainless steel has a high degree of finish and no residual oxide layer, which can significantly improve the flatness and polishing quality of the BA plate (the BA plate is a stainless steel plate that has been annealed and flattened, has a delicate surface, and can be directly used for subsequent processing of bright plates).

[0028] Example 2: 304 austenitic stainless steel S1-Pre-pickling operation: The main substances and their mass fractions in the pre-pickling solution in the pre-pickling tank are as follows: 20% hydrochloric acid and 0.8% benzotriazole; the stainless steel sample to be pickled is immersed in the pre-pickling solution for pre-pickling, the pickling temperature is 60°C, and the pickling residence time is 60 seconds; the pickled stainless steel sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; the pre-pickled stainless steel is obtained.

[0029] S2-1 level final pickling operation: the main substances and their mass fractions in the 1 level final pickling solution in the 1 level final pickling tank are as follows: 13% hydrochloric acid, 5% ferric chloride, 2% hydrogen peroxide and 2% p-hydroxybenzoic acid as a stabilizing additive; the pre-pickled stainless steel is immersed in the 1 level final pickling solution for 1 level final pickling, the pickling temperature is 60°C, the pickling residence time is 50 seconds, the pickled sample is washed with water at room temperature, and scrubbed with a scrubber for 5 seconds; and 1 level final pickled stainless steel is obtained.

[0030] S3-2 level final pickling operation: The main substances and their mass fractions in the level 2 final pickling solution in the level 2 final pickling tank are as follows: 11% hydrochloric acid, 5% ferric chloride, 1% hydrogen peroxide and 2% p-hydroxybenzoic acid as a stabilizing additive; immerse the level 1 final pickling stainless steel in the level 2 final pickling solution for level 2 final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain level 2 final pickling stainless steel.

[0031] S4-3-level final pickling and passivation operation: The main substances and their mass fractions in the 3-level final pickling solution in the 3-level final pickling tank are as follows: 2% hydrochloric acid, 5% hydrogen peroxide and 0.4% p-hydroxybenzoic acid as a stabilizing additive; immerse the 2-level final pickling stainless steel in the 3-level final pickling solution for 3-level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain 3-level final pickling passivated austenitic stainless steel.

[0032] The surface of the 3-level final pickling passivated austenitic stainless steel has a high degree of finish and no residual oxide layer, which can significantly improve the flat polishing quality of the BA plate. The 3D comparison of the microscopic plane of the stainless steel sample before and after pickling is shown in the figure below. Figure 1 and Figure 2 As shown, the average roughness before pickling was 2.82 and the average roughness after pickling was 1.86 as tested by scanning electron microscope.

[0033] Example 3: 304 austenitic stainless steel S1-Pre-pickling operation: The main substances and their mass fractions in the pre-pickling liquid in the pre-pickling tank are as follows: 18% hydrochloric acid and 0.6% ethylenediaminetetramethylenephosphonic acid; the stainless steel sample to be pickled is immersed in the pre-pickling liquid for pre-pickling, the pickling temperature is 60°C, and the pickling residence time is 60 seconds; the stainless steel sample after pickling is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; the pre-pickled stainless steel is obtained.

[0034] S2-1 level final pickling operation: the main substances and their mass fractions in the 1 level final pickling solution in the 1 level final pickling tank are as follows: 25% hydrochloric acid, 6% ferric chloride, 1% hydrogen peroxide and 1% acetoethoxyaniline as a stabilizing additive; the pre-pickled stainless steel is immersed in the 1 level final pickling solution for 1 level final pickling, the pickling temperature is 60°C, the pickling residence time is 50 seconds, the pickled sample is washed with water at room temperature, and scrubbed with a scrubber for 5 seconds; and 1 level final pickled stainless steel is obtained.

[0035] S3-2-level final pickling operation: The main substances and their mass fractions in the 2-level final pickling solution in the 2-level final pickling tank are as follows: 5% hydrochloric acid, 6% ferric chloride, 1% hydrogen peroxide and 1% acetoethoxyaniline as a stabilizing additive; immerse the 1-level final pickling stainless steel in the 2-level final pickling solution for 2-level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain 2-level final pickling stainless steel.

[0036] S4-3-level final pickling and passivation operation: The main substances and their mass fractions in the 3-level final pickling solution in the 3-level final pickling tank are as follows: 3% hydrochloric acid, 5% hydrogen peroxide and 0.3% acetoethoxyaniline as a stabilizing additive; immerse the 2-level final pickling stainless steel in the 3-level final pickling solution for 3-level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain 3-level final pickling passivated austenitic stainless steel.

[0037] The surface of the 3-level final pickling passivated austenitic stainless steel has a high degree of finish and no residual oxide layer, which can significantly improve the flatness and polishing quality of the BA plate.

[0038] Example 4: 316 austenitic stainless steel S1-Pre-pickling operation: The main substances and their mass fractions in the pre-pickling solution in the pre-pickling tank are as follows: 31% hydrochloric acid, 0.5% dihydroxybenzoic acid and 0.8% benzotriazole; the stainless steel sample to be pickled is immersed in the pre-pickling solution for pre-pickling, the pickling temperature is 70°C, and the pickling residence time is 60 seconds; the pickled stainless steel sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; the pre-pickled stainless steel is obtained.

[0039] S2-1 level final pickling operation: the main substances and their mass fractions in the 1 level final pickling solution in the 1 level final pickling tank are as follows: 25% hydrochloric acid, 3% ferric chloride, 2% hydrogen peroxide and 2% dihydroxybenzoic acid as a stabilizing additive; the pre-pickled stainless steel is immersed in the 1 level final pickling solution for 1 level final pickling, the pickling temperature is 60°C, the pickling residence time is 50 seconds, the pickled sample is washed with water at room temperature, and scrubbed with a scrubber for 5 seconds; and 1 level final pickled stainless steel is obtained.

[0040] S3-2 level final pickling operation: The main substances and their mass fractions in the level 2 final pickling solution in the level 2 final pickling tank are as follows: 15% hydrochloric acid, 5% ferric chloride, 1% hydrogen peroxide and 2% dihydroxybenzoic acid as a stabilizing additive; immerse the level 1 final pickling stainless steel in the level 2 final pickling solution for level 2 final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain level 2 final pickling stainless steel.

[0041] S4-3-level final pickling and passivation operation: The main substances and their mass fractions in the 3-level final pickling solution in the 3-level final pickling tank are as follows: 0.5% hydrochloric acid, 3% hydrogen peroxide and 0.5% dihydroxybenzoic acid as a stabilizing additive; immerse the 2-level final pickling stainless steel in the 3-level final pickling solution for 3-level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain 3-level final pickling passivated austenitic stainless steel.

[0042] The surface of the 3-level final pickling passivated austenitic stainless steel has a high degree of finish and no residual oxide layer, which can significantly improve the flat polishing quality of the BA plate. In addition, during the pre-pickling operation, although the mass fraction of hydrochloric acid reaches 31%, no irritating gas is generated due to the addition of the inhibitor dihydroxybenzoic acid.

[0043] Comparative Example 1: 304 austenitic stainless steel S1-Pre-pickling operation: The main substances and their mass fractions in the pre-pickling solution in the pre-pickling tank are as follows: 20% hydrochloric acid and 0.8% benzotriazole; the stainless steel sample to be pickled is immersed in the pre-pickling solution for pre-pickling, the pickling temperature is 60°C, and the pickling residence time is 60 seconds; the pickled stainless steel sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; the pre-pickled stainless steel is obtained.

[0044] S2-1 level final pickling operation: the main substances and their mass fractions in the 1 level final pickling solution in the 1 level final pickling tank are as follows: 25% hydrochloric acid, 3% ferric chloride, 2% hydrogen peroxide and 2% dihydroxybenzoic acid as a stabilizing additive; the pre-pickled stainless steel is immersed in the 1 level final pickling solution for 1 level final pickling, the pickling temperature is 80℃, the pickling residence time is 50 seconds, the pickled sample is washed with water at room temperature, and brushed with a brush scrubber for 5 seconds; and 1 level final pickled stainless steel is obtained.

[0045] S3-No 2nd level final pickling operation.

[0046] S4-No 3rd level final pickling and passivation operation.

[0047] There is a large amount of gray oxide layer remaining on the surface of the grade 1 final pickling stainless steel, and subsequent pickling treatment is still required.

[0048] Comparative Example 2: 304 austenitic stainless steel S1-Pre-pickling operation: The main substances and their mass fractions in the pre-pickling liquid in the pre-pickling tank are as follows: 18% hydrochloric acid and 0.6% ethylenediaminetetramethylenephosphonic acid; the stainless steel sample to be pickled is immersed in the pre-pickling liquid for pre-pickling, the pickling temperature is 60°C, and the pickling residence time is 60 seconds; the stainless steel sample after pickling is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; the pre-pickled stainless steel is obtained.

[0049] S2-1 level final pickling operation: the main substances and their mass fractions in the 1 level final pickling solution in the 1 level final pickling tank are as follows: 11% hydrochloric acid, 6% ferric chloride, 1% hydrogen peroxide and 1% acetoethoxyaniline as a stabilizing additive; the pre-pickled stainless steel is immersed in the 1 level final pickling solution for 1 level final pickling, the pickling temperature is 60°C, the pickling residence time is 50 seconds, the pickled sample is washed with water at room temperature, and scrubbed with a scrubber for 5 seconds; and 1 level final pickled stainless steel is obtained.

[0050] S3-No 2nd level final pickling operation.

[0051] S4-3-level final pickling and passivation operation: The main substances and their mass fractions in the 3-level final pickling solution in the 3-level final pickling tank are as follows: 2% concentration, 5% hydrogen peroxide and 0.3% acetoethoxyaniline as a stabilizing additive; immerse the 1-level final pickling stainless steel in the 3-level final pickling solution for 3-level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain 3-level final pickling passivated austenitic stainless steel.

[0052] The surface of the 3rd level final pickling passivated austenitic stainless steel has basically turned silver-white, but there is a small amount of stubborn gray oxide layer remaining.

[0053] Comparative Example 3: 316 austenitic stainless steel S1-Pre-pickling operation: The main substances and their mass fractions in the pre-pickling liquid in the pre-pickling tank are as follows: 15% hydrochloric acid and 0.6% ethylenediaminetetramethylenephosphonic acid; the stainless steel sample to be pickled is immersed in the pre-pickling liquid for pre-pickling, the pickling temperature is 60°C, and the pickling residence time is 60 seconds; the stainless steel sample after pickling is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; the pre-pickled stainless steel is obtained.

[0054] S2-1 level final pickling operation: the main substances and their mass fractions in the 1 level final pickling solution in the 1 level final pickling tank are as follows: 11% hydrochloric acid, 6% ferric chloride, 1% hydrogen peroxide and 1% acetoethoxyaniline as a stabilizing additive; the pre-pickled stainless steel is immersed in the 1 level final pickling solution for 1 level final pickling, the pickling temperature is 60°C, the pickling residence time is 50 seconds, the pickled sample is washed with water at room temperature, and scrubbed with a scrubber for 5 seconds; and 1 level final pickled stainless steel is obtained.

[0055] S3-2-level final pickling operation: The main substances and their mass fractions in the 2-level final pickling solution in the 2-level final pickling tank are as follows: 10% hydrochloric acid, 6% ferric chloride, 1% hydrogen peroxide and 1% acetoethoxyaniline as a stabilizing additive; immerse the 1-level final pickling stainless steel in the 2-level final pickling solution for 2-level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain a 2-level final pickling stainless steel.

[0056] S4-Re-2nd level final pickling operation: The main substances and their mass fractions in the 2nd level final pickling solution in the 2nd level final pickling tank are as follows: 10% hydrochloric acid, 6% ferric chloride, 1% hydrogen peroxide and 1% acetoethoxyaniline as a stabilizing additive; the stainless steel washed with 2nd level final pickling once is immersed in the 2nd level final pickling solution again for 2nd level final pickling, the pickling temperature is 50℃, the pickling residence time is 50 seconds, the sample after pickling is washed with water at room temperature, and brushed with a brushing machine for 5 seconds; stainless steel washed with 2nd level final pickling for multiple times is obtained.

[0057] S5-3-level final pickling and passivation operation: The main substances and their mass fractions in the 3-level final pickling solution in the 3-level final pickling tank are as follows: 2% hydrochloric acid, 5% hydrogen peroxide and 0.3% acetoethoxyaniline as a stabilizing additive; immerse the stainless steel that has been subjected to multiple 2-level final pickling in the 3-level final pickling solution for 3-level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain 3-level final pickling and passivated austenitic stainless steel.

[0058] The surface of the level 3 final pickling passivated austenitic stainless steel has obvious pitting pits and poor surface quality, and needs subsequent flattening treatment before processing.

[0059] Comparative Example 4: 316 austenitic stainless steel S1-Pre-pickling operation: The main substances and their mass fractions in the pre-pickling liquid in the pre-pickling tank are as follows: 31% hydrochloric acid; the stainless steel sample to be pickled is immersed in the pre-pickling liquid for pre-pickling, the pickling temperature is 70°C, and the pickling residence time is 60 seconds; the pickled stainless steel sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; the pre-pickled stainless steel is obtained.

[0060] S2-1 level final pickling operation: The main substances and their mass fractions in the 1 level final pickling solution in the 1 level final pickling tank are as follows: 18% hydrochloric acid, 3% ferric chloride, and 2% hydrogen peroxide; the pre-pickled stainless steel is immersed in the 1 level final pickling solution for 1 level final pickling, the pickling temperature is 60°C, the pickling residence time is 50 seconds, the pickled sample is washed with water at room temperature, and scrubbed with a scrubber for 5 seconds; and 1 level final pickled stainless steel is obtained.

[0061] S3-2 level final pickling operation: The main substances and their mass fractions in the level 2 final pickling solution in the level 2 final pickling tank are as follows: 10% hydrochloric acid, 5% ferric chloride, and 1% hydrogen peroxide; the level 1 final pickling stainless steel is immersed in the level 2 final pickling solution for level 2 final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, the pickled sample is washed with water at room temperature, and scrubbed with a scrubber for 5 seconds; and level 2 final pickling stainless steel is obtained.

[0062] S4-3-level final pickling and passivation operation: The main substances and their mass fractions in the 3-level final pickling solution in the 3-level final pickling tank are as follows: 1% hydrochloric acid and 3% hydrogen peroxide; immerse the 2-level final pickling stainless steel in the 3-level final pickling solution for 3-level final pickling, the pickling temperature is 50°C, the pickling residence time is 50 seconds, and the pickled sample is washed with water at room temperature and scrubbed with a scrubber for 5 seconds; obtain 3-level final pickling stainless steel.

[0063] The surface of the stainless steel after the 3rd level final pickling has a high degree of finish and no residual oxide layer, which can significantly improve the flatness and polishing quality of the BA plate. However, during the 1st and 2nd level final pickling processes, strong pungent gas is released (possibly harmful gases such as hypochlorous acid and chlorine), and a small amount of pungent gas is also released during the 3rd level final pickling.

Claims

1. A method for all-hydrochloric acid-based step pickling of austenitic stainless steel, characterized in that: Includes the following: The hot-rolled shot-peened austenitic stainless steel is directly subjected to full hydrochloric acid-based step pickling; The full hydrochloric acid-based cascade pickling process is divided into pre-pickling operation and final pickling operation; A pre-pickling solution is used for pre-pickling operation, wherein the pre-pickling solution mainly includes hydrochloric acid and a promoter additive, wherein the promoter additive includes one of 2-phosphonobutane-1,2,4-tricarboxylic acid, benzotriazole, and ethylenediaminetetramethylenephosphonic acid; The final pickling solution is used for the final pickling operation. The final pickling solution mainly includes hydrochloric acid, hydrogen peroxide, ferric chloride and a stabilizing additive. The stabilizing additive includes one of dihydroxybenzoic acid, p-hydroxybenzoic acid and acetoethoxyaniline.

2. A method for all-hydrochloric acid-based step pickling of austenitic stainless steel according to claim 1, characterized in that: The mass concentration of hydrochloric acid in the pre-pickling solution is 10% to 31%, and the mass concentration of the promoting additive is 0.1% to 1%.

3. A method for all-hydrochloric acid-based step pickling of austenitic stainless steel according to claim 2, characterized in that: When the mass concentration of hydrochloric acid in the pre-pickling solution is ≥28%, a stabilizing additive needs to be added.

4. A method for all-hydrochloric acid-based step pickling of austenitic stainless steel according to claim 3, characterized in that: The stabilizing additive includes one of dihydroxybenzoic acid, p-hydroxybenzoic acid, and acetoethoxyaniline, and the mass concentration of the stabilizing additive in the pre-pickling solution is 0.3% to 2%.

5. The method for full hydrochloric acid-based step pickling of austenitic stainless steel according to claim 1, characterized in that: The pickling temperature of the pre-pickling operation is 40℃~80℃, and the time is 20s~70s.

6. A method for all-hydrochloric acid-based step pickling of austenitic stainless steel according to claim 1, characterized in that: The final pickling operation includes: S2-1 level final pickling operation, S3-2 level final pickling operation, S4-3 level final pickling passivation operation.

7. A method for all-hydrochloric acid-based step pickling of austenitic stainless steel according to claim 6, characterized in that: A level 1 final pickling solution is used for the level 1 final pickling operation. The mass concentrations of the substances in the level 1 final pickling solution are as follows: hydrochloric acid 5%~25%, hydrogen peroxide 0.5%~3%, ferric chloride 4%~10%, and stabilizing additives 0.3%~2%.

8. A method for all-hydrochloric acid-based step pickling of austenitic stainless steel according to claim 6, characterized in that: A second-level final pickling solution is used for the second-level final pickling operation. The mass concentrations of the substances in the second-level final pickling solution are as follows: hydrochloric acid 5%~25%, hydrogen peroxide 0.5%~3%, ferric chloride 4%~10%, and stabilizing additives 0.3%~2%.

9. A method for all-hydrochloric acid-based step pickling of austenitic stainless steel according to claim 6, characterized in that: A 3-level final pickling solution is used for the 3-level final pickling and passivation operation. The mass concentration of each substance in the 3-level final pickling solution is as follows: hydrochloric acid 0.5%~3%, hydrogen peroxide 2%~6%, and stabilizing additive 0.1%~0.5%.

10. A method for all-hydrochloric acid-based step pickling of austenitic stainless steel according to claim 6, characterized in that: The pickling temperature of the first-level final pickling operation is 20℃~70℃, and the time is 20s~70s; the pickling temperature of the second-level final pickling operation is 20℃~70℃, and the time is 20s~70s; the pickling temperature of the third-level final pickling and passivation operation is 20℃~50℃, and the time is 20s~70s.

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