STEEL SHEET FOR DISSIMILAR MATERIALS WELDBONDING TO ALUMINUM MATERIAL AND DISSIMILAR MATERIALS BONDED BODY

摘要

A steel sheet for use in weld bonding to an aluminiummaterial, comprises, in mass, C: 0.02 to 0.3%, Si: 0.2 to5.0%, Mn: 0.2 to 2.0%, and Al: 0.002 to 0.1%, further one ormore of Ti: 0.005 to 0.10%, Nb: 0.005 to 0.10%, Cr: 0.05 to1.0%, and Mo: 0.01 to 1.0%, and the balance consisting of Feand unavoidable impurities. In the steel sheet, (i) theproportion of oxide containing Mn and Si by 1 at.% or more intotal in a newly formed external oxide layer is 50 to 80 % ofthe average proportion of the total length of the oxide to 1µm length of the interface between the base steel material andexternal oxide layer; (ii) the proportion of internal oxide,including oxide at the grain boundary, existing up to a depthof 10 µm2 of the steel region; and (iii) the proportion ofinternal oxide, including oxide at the grain boundary,existing in the steel region exceeding 10 µm in depth from thebase steel material surface and containing Mn and Si by 1 at.%or more in total is 0.1% or less in terms of the average areapercentage of internal oxide in the visual field of 10 µm2 ofthe steel region.