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Hot-rolled stainless steel sheets mainly include austenitic stainless steel sheets and ferritic/martensitic stainless steel sheets. Their typical grades are type 18-8 (18% Cr + 8%-9% Ni) and type Cr13. The former is pickled after solution treatment, while the latter is pickled after annealing. The heat treatment temperature range is wide, and the composition and structure of the oxide scale vary, which leads to differences in the pickling methods as well. After heat treatment and straightening, most of the oxide scale on 18-8 austenitic stainless steel sheets falls off. The scale that is firmly bonded to the steel plate is only 0.05 mm thick. Analysis of the scale that peels off from 0cr19ni9 steel shows that its composition consists of 6.61% FeO, 80.54% Fe3O2, 9.44% Cr2O3, along with a small amount of NiO. Such stainless steel plates are washed in an acid bath for 5–25 minutes; the temperature of the acid bath ranges from 60–80 degrees Celsius, with typical operating temperatures being around 70–75 degrees Celsius. During pickling, in addition to controlling the acid concentration, the content of NaCl also needs to be controlled. When the NaCl content is low (less than 5 g/L), the surface color of the steel plate is not bright; whereas when the NaCl content is too high (greater than 26 g/L), pitting is likely to occur. If the acid temperature is too high (above 85 degrees Celsius) or the pickling time is too long (above 60 minutes), the surface of the steel sheet turns black after pickling. Upon inspection under magnification, significant corrosion had occurred on the surface of the plate. During the pickling process, it is necessary to monitor the condition of the solution in the pickling tank; the reaction of the stainless steel sheets in the tank is calm at first, but after a few minutes the solution becomes turbulent and the reaction intensifies. The bubbling phenomenon indicates that a large amount of hydrogen gas has been generated; the steel plate should not remain in the acid tank any longer. It is better to keep the total pickling time within 5–20 minutes. The color of the acid solution differs when it is freshly prepared and just before it is discharged, so it is necessary to regularly check the test results and observe any changes in the solution’s color. The newly prepared solution should be clear, while it becomes turbid and darker near the time of discharge, taking on a dark green color due to high levels of ferrous sulfate. The steel plate was lifted out of the acid tank; its surface had a thick coating, giving it an ink-green color. These situations indicate that the pickling solution should be replaced. Jiangsu Xinbaifa Stainless Steel Co., Ltd. sells stainless steel sheets of materials such as 304, 321, 316L, 309s, 310s, 2205, 2507, 904L, 317L, etc., all year round. www.xbfbxg.com