Steel sheet hot-dip-coated with Zn-Al-Mg-based system, and process of manufacturing same

摘要

The present invention provides a steel sheet hot-dip-coated with a Zn-Al-Mg-based system for welded structural members, which can be used as a steel material suitable for an arc-welded structural member and which is significantly improved in all of burring workability, molten metal embrittlement cracking resistance, and corrosion resistance at welded parts. This steel sheet hot-dip-coated with a Zn-Al-Mg-based system for welded structural members has a Zn-Al-Mg-based hot-dip coating layer on the surface of a base steel sheet, wherein the base steel sheet has a specified chemical composition and has such a metallic structure that Ti-containing precipitates having an average particle diameter of 20 nm or smaller are dispersed in a matrix composed of a ferrite phase, and the relationship between the contents of steel components and the thickness (t) (mm) in the base steel material is such a relationship that a molten metal embrittlement cracking sensitivity index (H3 value) represented by formula (3) is 2.90 or less. H3 value = C/0.2+Si/5.0+Mn/1.3+Cr/1.0+Mo/1.2+0.4t-0.7(Cr+Mo)