Surface treatment process of stainless steel strip after cold rolling

The removal of iron scale on the surface of hot-rolled stainless steel strip is usually a combination of mechanical and chemical methods. Mechanical methods mainly include shot blasting, scale breaking and steel brush cleaning. Because the surface cracks are all inside the iron scale layer, these are relatively easy to remove.

Stainless steel with 2B surface
At present, the annealing and pickling lines of many steel mills are equipped with shot blasting and steel brushing equipment. Shot blasting equipment can make the surface soft according to the choice of particle size, and the steel brush device can remove the adhesion and re-adhesion of iron scale.
The chemical method is mainly pickling, most of which use a mixed acid of nitric acid and hydrofluoric acid to remove iron scale, and sometimes hydrochloric acid and sulfuric acid are used alone or in combination.
For steel grades prone to surface defects, abrasive belt polishing machines can also be used to remove surface defects, followed by shot peening and pickling, so that the processing color similar to No.1 can be obtained.
The process of cold-rolling hot-rolled stainless steel coils and then annealing and pickling is called NO.2D processing. The hardness of the cold roll is higher than that of the hot roll, and the metal structure is finer, and the polishing is also processed with a fine-grained number. Since the surface finish of NO.2 processing is better than that of NO.1, in order to make the cold-rolled surface better, the total reduction rate and the reduction rate of each pass must be properly distributed, and the stainless steel strip needs to be annealed and pickled. The annealed iron scale of cold-rolled stainless steel strip products is weaker than that of hot-rolled stainless steel strip. Therefore, do not use mechanical descaling method on the product annealing and pickling line, but should be immersed in alkaline salt and neutral water tank, and then removed by sulfuric acid electrolysis, aqua regia or mixed acid of nitric acid and hydrofluoric acid.
Temper rolling is a process of 0.2%-2% reduction processing with large-diameter mirror-finished rolls after annealing and pickling. Its function is to avoid twill defects when ferritic stainless steel is used for slip line processing; after processing the surface of austenitic stainless steel with 2B gloss, the metal surface will show a slightly white luster. This whiteness is due to the residue on the surface. It is caused by random reflection of traces of a little grain boundary.
There is also a surface that is bright annealed, and the processed surface is a BA surface, and its brightness is better than that of 2B. Bright annealing is annealed in an inert gas, so the rolled surface can be obtained without pickling. The inert gas uses the decomposition gas of ammonia and pure hydrogen. Electric heating is used for heating or heating with a radiant tube furnace, while cooling is to blow inert gas into the furnace for cooling, and then take the stainless steel strip out of the furnace after waiting for normal temperature. Among them, in order to obtain the best possible surface, before annealing, it is necessary to fully remove the attachments such as lubricating oil, avoid the immersion of external air, and control the dew point of the atmosphere to a minimum as much as possible, which is Most importantly, it requires extra attention.