POSCO Holdings Inc.
HIGH STRENGTH COLD-ROLLED STEEL SHEET HAVING EXCELLENT YIELD STRENGTH, DUCTILITY, AND HOLE EXPANDABILITY, HOT-DIP GALVANIZED STEEL SHEET, AND METHOD FOR PRODUCING SAME

Abstract:

Provided are a high strength cold rolled steel plate having excellent yield strength, ductility, and hole expandability, a hot dip galvanized steel plate, and a method for producing the same. The cold rolled steel plate of the present invention comprises 0.06-0.2 wt % of carbon (C), 1.5-3.0 wt % of manganese (Mn), 0.3-2.5 wt % of silicon (Si), 0.01-0.2 wt % of aluminum (Al), 0.01-3.0 wt % of nickel (Ni), 0.2 wt % or less of molybdenum (Mo), 0.01-0.05 wt % of titanium (Ti), 0.02-0.05 wt % of antimony (Sb), 0.0005-0.003 wt % of boron (B), 0.01 wt % or less (but not 0%) of nitrogen (N), with the remainder comprising Fe and unavoidable impurities, and the microstructure thereof comprises, in terms of area fraction, 50% or more of bainite, 10% or more of tempered martensite (TM), 10% or less of fresh martensite (FM), 20% or less of residual austenite, and 5% or less of ferrite.