Crack Spacing Distribution in Coating Layer of Galvannealed Steel under Applied Tensile Strain

抄録

The crack spacing distribution of the Fe–Zn intermetallic coating layer of tensile-strained galvannealed IF (Interstitial Free) and SPCC (Steel Plate Cold Commercial, Japanese Industrial Standard) steels under tensile applied strain at room temperature was studied. The experimental and analytical results revealed that the crack spacing decreases with increasing applied strain due to the increase in stress transfer efficiency and the cumulative probability–crack spacing curves at any applied strain of both samples lie in a unique curve when the crack spacing is normalized with respect to the average value at each applied tensile strain. Then, by combining these features, a comprehensive description method of the crack spacing distribution was proposed, in which the influences of the thickness of the coating layer, substrate material and applied strain are incorporated. With the proposed method, the measured change of the probability density–crack spacing curve with increasing applied strain was described well for both samples. Also with this method, the variation of the probability density–crack spacing relation as a function of applied strain was predicted for different thickness of the coating layer and substrate material. Based on these results, the influences of multiple cracking that takes place in advance of spalling of the coating layer on the non-uniform spalling and the influences of thickness of the coating layer and substrate material on the spalling behavior were discussed.