HIGH-STRENGTH HIGH-WORKABILITY COLD ROLLED STEEL SHEET HAVING EXCELLENT IMPACT RESISTANCE

摘要

The present invention relates to cold rolled steel sheet with high strength and high formability having an excellent crushing performance which is characterized in that said steel sheet contains 0.05-0.40 mass % of C, 1.0-3.0 mass % of Si, 0.6-3.0 mass % of Mn, 0.02-1.5 mass % of Cr, 0.010-0.20 mass % of P and 0.01-0.3 mass % of Al while the remained part substantially consists of Fe; that said steel sheet has ferrite (polygonal ferrite) as a major phase and has a minor phase consisting of martensite, acicular ferrite and retained austenite; that the ratio of the minor phase in the steel structure is 3-40%; and that the ratios of martensite, retained austenite and acicular ferrite in the minor phase are 10-80%, 8-30% and 5-60%, respectively. In accordance with the present invention, it is now possible to offer cold rolled steel sheet with high strength and high formability having an excellent crushing performance which not only exhibits a sufficient formability mostly as a steel sheet for automobiles but also is capable of satisfying a severe safety standard.