POSCO Holdings Inc.
HIGH-STRENGTH HOT-ROLLED STEEL SHEET HAVING EXCELLENT BLANKING PROPERTIES AND UNIFORMITY, AND MANUFACTURING METHOD THEREOF

Abstract:

The present invention provides a steel sheet comprising by weight: C: 0.10-0.30%; Si: 0.001-1.0%; Mn: 0.5-2.5%; Cr: 0.001-1.5%; Mo: 0.001-0.5%; Al: 0.001-0.5%; P: 0.001-0.01%; S: 0.001-0.01%; N: 0.001-0.01%; B: 0.0001-0.004%; Ti: 0.001-0.1%; Nb: 0.001 to 0.1%; and the balance consisting of Fe and inevitable impurities, and satisfying relational expression (1), and a microstructure includes comprising: a martensite phase; a bainite phase, wherein the fraction of the martensite phase is 50-90%, the fraction of the bainite phase is 5-50%, the sum of the fractions of the martensite phase and the bainite phase is 90% or more; and the balance consisting of a ferrite phase. CL<1, [Relationship Expression (1)] CL=-0.692-0.158.times.[Mn]+0.121.times.[Mn].sup.2+0.061.times.[Cr].sup.2-- 0.319.times.[Mo]+0.035.times.[Hardness_HRC] (where CL is an effective cracking index, [Mn], [Cr] and [Mo] are the percentages by weight of respective corresponding alloy elements, and [Hardness_HRC] is a Rockwell hardness (HRC).)