Acid pickling of hot rolled stainless steel strip

- Jan 25, 2019 -

In the scale, the rich body structure is only present on the surface close to the stainless steel plate, and the outer layers of the iron sheet Fe3O4 and Fe2O3 are more difficult to dissolve in the acid solution. However, because there are cracks and pores in the iron layer, especially after breaking the scale or pulling the correction, the acid solution is more likely to pass through the cracks and pores to the surface of the stainless steel strip and the rich layer, along with the metal iron and the rich body. Dissolution will reduce the adhesion between the iron sheet and the stainless steel strip, and under the action of hydrogen formed during the reaction between the acid solution and the stainless steel strip, the scale will fall off the substrate and sink to the bottom of the acid tank. At the same time, the insoluble Fe3O4 and Fe2O3 are also reduced to readily soluble FeO in order to separate the scale from the surface of the strip.

 

Another important factor affecting the pickling of stainless steel is the density of the iron sheet. The rich body has a natural maximum pore, and the Fe2O3 layer and the Fe3O4 layer are dense, and they block all the pores in the other oxide layer in the iron sheet, thereby hindering the penetration of the acid solution. Although the stainless steel strip will generate some cracks during the cooling process, it cannot ensure that the acid penetrates into the depth of the scale. Especially for hot-rolled strip produced by modern rolling mills, the thickness of the iron sheet is very stable and the density is very high. Therefore, in order to enhance the pickling property of the scale, it is still necessary to increase the crack by using the scale-reducing equipment.

 

The iron oxide scale on the surface of the stainless steel strip tail is easier to wash off during pickling. This is because the rolling temperature of the stainless steel strip tail is usually 30-50 ° C lower than the middle and the head, and is reinforced by the water falling from the coiler during the coiling, so the stainless steel strip tail iron is formed. The process ends early, the iron oxide scale is thinner, and FeO is too late to convert.

 


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