HIGH-STRENGTH STEEL SHEET FOR WARM PRESS FORMING AND METHOD FOR MANUFACTURING THEREOF

摘要

Provided are a high-strength steel sheet which has satisfactory warm formability and which, after having been warm-formed, has excellent strength and ductility and a process for producing the high-strength steel sheet. The high-strength steel sheet has a room-temperature tensile strength of 780 MPa or higher. The yield stress thereof measured in the heating-temperature range of 400-700ºC is 80% or less of the room-temperature yield stress thereof. The total elongation thereof measured in the heating-temperature range is at least 1.1 times the room-temperature total elongation thereof. The steel sheet which was heated to the heating-temperature range, deformed at a strain of 20% or less, and then cooled from the heating temperature to room temperature has a yield stress that is 70% or more of the room-temperature yield stress thereof measured before the heating. The steel sheet which was heated to the heating-temperature range, deformed at a strain of 20% or less, and then cooled from the heating temperature to room temperature has a total elongation that is 70% or more of the room-temperature total elongation thereof measured before the heating.