HIGH STRENGTH HOT ROLLED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME

摘要

There is provided a high strength hot rolled steel sheet having a composition comprising C: 0.040% to 0.100%, by mass %, Si: 0.50% or less, by mass %, Mn: 1.00% to 2.00%, by mass %, P: 0.03% or less, by mass %, S: 0.006% or less, by mass %, Al: 0.08% or less, by mass %, N: 0.0080% or less, by mass %, Ti: 0.14% to 0.22%, by mass %, and Fe and incidental impurities, and a method for making the same. The high strength hot rolled steel sheet includes a microstructure in which a primary phase is a ferrite phase and fine carbides containing Ti are dispersion-precipitated.

主权项

1. A high strength hot rolled steel sheet having a composition comprising:
C: 0.040% to 0.100%, by mass %; Si: 0.50% or less, by mass %; Mn: 1.00% to 2.00%, by mass %; P: 0.03% or less, by mass %; S: 0.006% or less, by mass %; Al: 0.08% or less, by mass %; N: 0.0080% or less, by mass %; Ti: 0.14% to 0.22%, by mass %; and Fe and incidental impurities, wherein the high strength hot rolled steel sheet includes a microstructure in which a primary phase is a ferrite phase and fine carbides containing Ti are dispersion-precipitated, in each of an end portion and a central portion of the steel sheet the sheet width direction, the area ratio of the ferrite phase is in the range of 95% or more, the average grain size of the ferrite phase is in the range of 5.0 μm or less, the average particle diameter of the fine carbides is in the range of 6 nm or less, and the amount of solid solution Ti is in the range of 0.03% or less, by mass %, and the steel sheet has a yield strength in the range of 740 MPa or more and a difference between the yield strength of the end portion in the sheet width direction and the yield strength of the central portion in the sheet width direction is in the range of 50 MPa or less.