Causes Analysis on Micro-Cracks of 6Cr13 Stainless Steel Plate of Cutlery Material after Cold Rolling

After three times of cold-rolling process and standing for a week, densely distributed micro-cracks appeared in the 6Cr13 martensitic stainless steel plate. The crack forming causes were determined by analyzing the chemical composition, microstructure, surface morphology, hardness and micro-zone compositions of the steel plate. The results show that due to the high chromium content in the local carbides of the raw material, the phenomenon of poor chromium appeared in the carbides periphery, which reduced the corrosion resistance of the material. When the steel plate was exposed to chloride ions, pitting corrosion of the chromium deficient area occurred. With the development of the corrosion, the pH of the pit medium reduced to acidic because of the concentration and hydrolysis of chlorides in the pits. Hydrogen ions obtained electrons and became hydrogen atoms by electrochemical reaction, and then the hydrogen atoms enriched at the local position and produced hydrogen pressure. Under the combined action of hydrogen and rolling residual stress, hydrogen-induced cracking occurred along the rolling direction. Finally, according to the formation causes of micro-cracks of the steel plate, suggestions such as lengthening annealing time and improving compositions were proposed.