HIGH STRENGTH HOT ROLLED STEEL SHEET EXCELLENT IN STRETCH FLANGE-ABILITY AND LOW TEMPERATURE TOUGHNESS AND HAVING MAXIMUM TENSILE STRENGTH OF 980 MPa OR MORE AND PRODUCTION METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet excellent in stretch flange-ability and low temperature toughness and having a maximum tensile strength of 980 MPa or more, and a production method therefor.SOLUTION: The high strength hot rolled steel sheet excellent in stretch flange-ability and low temperature toughness and having a maximum tensile strength of 980 MPa or more is provided which has a chemical composition containing, by mass%, C:0.01 to 0.20%, Si:2.50% or less (excluding 0), Mn:4.00% or less (excluding 0), P:0.10% or less (excluding 0), S:0.03% or less (excluding 0), Al:0.001 to 2.00%, N:0.01% or less (excluding 0), O:0.01% or less (excluding 0), one or two kind of Ti and Nb: 0.01 to 0.30% in total and the balance iron with inevitable impurities and which has a micro structure containing one or both of tempered martensite and lower bainite of total 90% or more by volume fraction and has a standard deviation of Vickers hardness distribution &sgr; of 15 or less.