Jfe Steel Corporation

Tamako Ariga

Yoshimasa Funakawa

Takeshi Yokota

Akio Kobayashi

Kazuhiro Seto

Takayuki Murata

Katsumi Nakajima

Noriaki Moriyasu

Tetsuya Mega

Hiroshi Owada

Hiroshi Uchomae

Tetsuo Yamamoto

Yasunobu Uchida

Described is a high tensile strength hot rolled steel sheet having high strength and formability, and a manufacturing method. It has tensile strength &#x2267;980 MPa and excellent formability, and specifically identified ranges by mass % of C, Si, Mn, P, S, N, Al, Ti, V, Solute V, and Solute Ti; (ii) microstructure with fine carbides dispersion precipitated therein, the fine carbides containing Ti and V and having the average particle diameter &#x3c;10 nm, as well as volume ratio with respect to the entire microstructure &#x2267;0.007; and matrix as ferrite phase having area ratio with respect to the entire microstructure &#x2267;97%. C, Ti, V, S and N satisfy (1) Ti&#x2267;0.08 +(N/14&#xd7;48+S/32&#xd7;48) and (2) 0.8&#x2266;(Ti/48+V/51)/(C/12)&#x2266;1.2, where 'C', 'Ti', &#x201c;V&#x201d;, &#x201c;S&#x201d; and &#x201c;N&#x201d; represent contents (mass %) of corresponding elements, respectively.

High tensile strength hot rolled steel sheet having excellent formability and method for manufacturing the same

A high tensile steel sheet having 980 MPa or higher tensile strength with excellent elongation and stretch-flange formability, suitable for the press-forming of complex cross sectional shape such as automobile parts, is manufactured by adjusting the steel to consist essential of a ferrite single phase structure, to precipitate carbide containing Ti, Mo, and V, of smaller than 10 nm of average particle size, in dispersed state, and to have an average composition of the carbide containing Ti, Mo, and V satisfying [V/(Ti+Mo+V)&#x2267;0.3 (atomic ratio].

High strength steel sheet and method for manufacturing the same

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Tokyo, Japan

Tamako Ariga