Effects of compressive pre-strain on susceptibility to liquid zinc induced cracking of 590MPa class steels

摘要

This paper describe the effects of compressive pre-strain on susceptibility to liquid zinc induced cracking of 590MPa class steels. It was reported by the authors that liquid zinc induced crackings occurred, in some cases, at the toes of fillet welds between 590MPa class steel tubes and ring-plates during a hot-dip galvanizing. The mechanism could be explained with plastic compressive bending moment due to the temperature difference between the tube and the ring-plate at the initial stage of the galvanizing. As the temperature difference decreased with a time elapsed, the bending moment decreased to convert compressive stress to tensile stress. Zinc induced cracking could occur under tensile stress. There have been neither experimental data nor testing methods so far to refer to the effects of the compressive pre-strain on susceptibility to liquid zinc induced cracking. In this research, critical strains for crack initiation (ε{sub}c) of several 590MPa class steels with some compressive pre-strain were measured by a newly developed testing method. The compressive pre-strain (ε{sub}p) has an effect to lower the value ε{sub}c. And also, the tensile deformation rate (V) and Carbon Equivalent for Zinc induced cracking (CEZ) correlate well with the value of ε{sub}c respectively. As a result, ε{sub}c can be estimated from the parameters of ε{sub}p, V and CEZ. These results will be useful information to prevent liquid zinc induced cracking in pipe structures.