Jfe Steel Corporation

Masahide Watabe

Shinjiro Kaneko

Yasushi Tanaka

Kazuhiro Seto

Kaneharu Okuda

Reiko Sugihara

Noriaki Kohsaka

Tetsuo Shimizu

Noriaki Moriyasu

A high-strength hot-rolled steel sheet has a tensile strength (TS) of 540 to 780 MPa, only small variations in strength, and excellent uniformity in strength using a general-purpose Ti-containing steel sheet, which is inexpensive. The high-strength hot-rolled steel sheet includes, on a mass percent basis, 0.05%-0.12% C, 0.5% or less Si, 0.8%-1.8% Mn, 0.030% or less P, 0.01% or less S, 0.005%-0.1% Al, 0.01% or less N, 0.030%-0.080% Ti, and the balance being Fe and incidental impurities. The microstructure have a bainitic ferrite fraction of 70% or more, and the amount of Ti present in a precipitate having a size of less than 20 nm is 50% or more of the value of Ti* calculated using formula (1): Ti*=[Ti]&#x2212;48/14&#xd7;[N] (1) where [Ti] and [N] represent a Ti content (percent by mass) and a N content (percent by mass), respectively, of the steel sheet.

High-strength hot-rolled steel sheet and method for manufacturing same

A steel sheet contains, on a mass percent basis, 0.03%-0.12% C, 0.5% or less Si, 0.8%-1.8% Mn, 0.030% or less P, 0.01% or less S, 0.005%-0.1% Al, 0.01% or less N, 0.035%-0.100% Ti, and the balance being Fe and incidental impurities and has microstructures with a fraction of polygonal ferrite of 80% or more, the polygonal ferrite having an average grain size of 5 to 10 &#x3bc;m. The amount of Ti present in a precipitate having a size of less than 20 nm is 70% or more of the value of Ti* calculated using expression (1):Ti*=[Ti]&#x2212;48&#xd7;[N]/14&#x2003;&#x2003;(1)

High-strength hot-rolled steel sheet and method for manufacturing the same

Growing community of inventors

Tokyo, Japan

Masahide Watabe