溶融亜鉛めっき割れに及ぼす曲げ加工の影響

抄録

It is well-known that liquid zinc-induced cracking occurs at the heat affected zone when the welded steel structures are immersed in the liquid zinc. The composition, the microstructure and the hardness of steel are related to this crack. Moreover, this crack is caused by bending work, but there has been no systematic research paper published on this to date. In this research, the influences of the bending work level and the degree of cleanness for steel surface with liquid zinc induced cracking were examined. The following results were obtained. The liquid zinc-induced cracking was caused by only bending work when the residual stresses induced by bending work were over 680MPa. When the residual stresses were under 680MPa, the cracking was caused at the yield stress of steel. The liquid zinc-induced cracking initiated at the grain boundaries of the steel surface opened by bending work and propagated along the grain boundaries of ferrite or the interface of ferrite and pearlite. The liquid zinc-induced cracking from bending work was able to be prevented when the surface of steel was ground by 100μm.