(1) Hot rolling mill
Hot rolled coils must be pickled before being cold rolled. The pickling has the following functions:
1. Remove iron oxide skin generated during hot rolling;
2. Trim the side of the strip;
3. Apply rolling lubricating oil to prevent rust and lubrication;
4. Check and remove various surface defects that are harmful to subsequent cold rolling and other processes;
(2) Hot rolling conditions
The final rolling stability and coiling temperature of the hot rolling have a great influence on the mechanical properties of the tin-plated original sheet produced by cold rolling and annealing. In general, it is desirable that the final rolling temperature is higher and the coiling temperature is lower to make the crystals The particle size becomes finer and the carbides are finely dispersed.
Lower finish rolling temperature, higher coiling temperature, softer material, but large fluctuations in performance; conversely, the material becomes hard (dispersion strengthened), and the performance fluctuation is small and stable.
(3) Iron oxide skin:
Iron oxide composition:
The formation of scale on the hot-rolled strip surface is a reaction process in which atmospheric oxygen diffuses to the inside. The outermost layer is a very thin layer of ferric oxide, and the middle is a later layer of ferro-ferric oxide. The inner layer is the last. Ferrous oxide layer. During the pickling process, the structure of the internal iron oxide layer dissolves and the scale peels off.
The scale formed on the surface of the hot rolled steel strip is very harmful both for the steps after pickling and for the tinplate of the final product. E.g:
The strip rolling with the residual iron oxide skin will cause defects in the rolling stick, and it will also press the scale into the strip steel, which will cause defects in the tin plating layer, affecting the anti-rust performance and processing performance.