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1. (WO2018080133) ULTRA-HIGH-STRENGTH STEEL SHEET HAVING EXCELLENT HOLE EXPANDABILITY AND YIELD RATIO AND METHOD FOR PREPARING SAME

Pub. No.:    WO/2018/080133    International Application No.:    PCT/KR2017/011765
Publication Date: Fri May 04 01:59:59 CEST 2018 International Filing Date: Wed Oct 25 01:59:59 CEST 2017
IPC: C22C 38/04
C22C 38/02
C22C 38/06
C22C 38/60
C22C 38/14
C22C 38/12
C21D 8/02
Applicants: POSCO
주식회사 포스코
Inventors: RYU, Joo-Hyun
류주현
LEE, Kyoo-Young
이규영
LEE, Sea-Woong
이세웅
LEE, Won-Hwi
이원휘
Title: ULTRA-HIGH-STRENGTH STEEL SHEET HAVING EXCELLENT HOLE EXPANDABILITY AND YIELD RATIO AND METHOD FOR PREPARING SAME
Abstract:
An aspect of the present invention relates to an ultra-high-strength steel sheet having excellent hole expandability and yield ratio, the ultra-high-strength steel sheet comprising, in terms of wt%, 0.05-0.2% of C, 2.0% or less of Si, 4.1-9.0% of Mn, 0.05% or less (excluding 0%) of P, 0.02% or less (excluding 0%) of S, 0.5% or less (excluding 0%) of Al, 0.02% or less (excluding 0%) of N, and the balance Fe and other inevitable impurities, wherein the ultra-high-strength steel sheet comprises at least one selected from 0.1% or less (excluding 0%) of Ti, 0.1% or less (excluding 0%) of Nb, 0.2% or less (excluding 0%) of V, and 0.5% or less (excluding 0%) of Mo, and satisfies relational formula 1 below, and wherein the microstructure thereof comprises, in terms of percent by volume, 10-30% of residual austenite, 50% or more of annealed martensite, and 20% or less of the other phases comprising alpha martensite and epsilon martensite. Relational formula 1: C/12 + Ti/48 + Nb/93 + V/51 + Mo/96 ≥ 0.015 (in relational formula 1, each element symbol represents a value of the content of each element in wt%).