Effect of Production Technological Parameters on Corrosion Resistance of Ultralow-Carbon Cold-Rolled IF-Steels

The influence of production technological parameters on corrosion resistance of cold-rolled ultralow-carbon IF-steels of various compositions (0.003-0.005 wt.% C, 0.54-0.71 wt.% Ti) is studied. Analysis of the microstructure and chemical composition shows that grain size and composition changes in the range studied do not affect corrosion resistance. Mechanical tests reveal a correlation between the corrosion rate and rolled product yield strength. Statistical analysis methods are used to determine the key temperature parameters of hot rolling and processing in continuous annealing units (CAU). It is found that corrosion resistance depends on the speed of strip movement in a CAU, and temperatures at the exit from the heating and holding sections. It is shown that corrosion rate is mainly determined by the state of solid solution formed in the over-ageing sections of the CAU and during subsequent cooling. With a reduction in strip movement rate the ageing processes develop to a greater extent leading to formation of carbon segregations at dislocations that play the role of anodic areas.