High strength steel sheet, high strength hot dip galvanized steel plate and high strength alloyed hot dip galvanized steel plate having excellent tensile strength with tensile maximum strength of 780 MPa or more

摘要

PROBLEM TO BE SOLVED: To provide a high strength steel sheet, high strength hot-dip galvanized steel sheet and high strength hot-dip galvannealed steel sheet each having a maximum tensile strength (TS) of 780 MPa or more and applicable to an impact absorption member upon impact.SOLUTION: The high strength steel sheet having a maximum tensile strength of 780 MPa or more and excellent in collision characteristic is provided that has a micro structure containing ferrite of 30% or more as a main phase by volume fraction, one or more kind of martensite and bainite of 10 to 70% or less in total as a second phase and retained austenite limited to less than 10% by volume fraction and that has a ratio between a deformation stress in a forward direction (z) and a deformation stress in a reverse direction (-z) in a Bauschinger test satisfying the following (1) formula. |(-z)|/|(z)|0.85 (1).