Jfe Steel Corporation

Tetsuo Yamamoto

Yoshimasa Funakawa

Hiroshi Nakano

Taro Kizu

Hiroshi Uchomae

Takeshi Yokota

Akio Kobayashi

Kazuhiro Seto

Toru Hoshi

Nobuyuki Kageyama

A method of manufacturing a high-strength hot rolled steel sheet by hot rolling a steel having a chemical composition including, by mass %: C: more than 0.010% and not more than 0.06%, Si: not more than 0.3%, Mn: not more than 0.8%, P: not more than 0.03%, S: not more than 0.02%, Al: not more than 0.1%, N: not more than 0.01% and Ti: 0.05 to 0.10%, the balance including Fe and inevitable impurities, including: after the steel is heated to an austenite single phase region, the steel is finish rolled at a finishing delivery temperature of 860&#xb0; C. to 1050&#xb0; C., the steel sheet is cooled at an average cooling rate of not less than 30&#xb0; C./s in a temperature range of from a temperature after the completion of the finish rolling to 750&#xb0; C., and the steel sheet is coiled into a coil at a coiling temperature of 580&#xb0; C. to 700&#xb0; C.

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

A high-strength hot rolled steel sheets with excellent stretch flangeability has small variations in mechanical properties in individual coils. Variations in strength from place to place in a coil are decreased by minimally reducing the Si and Mn contents to suppress the occurrence of problems such as segregation. Further, the microstructure of the steel sheets is configured such that a ferrite phase represents an area ratio of not less than 95%, the ferrite crystal grains have an average grain size of not less than 1 &#x3bc;m, and the ferrite crystal grains contain TiC with an average particle size of not more than 7 nm dispersed in the crystal grains.

High-strength hot rolled steel sheet

A hot-pressed steel sheet member has a composition containing, by mass, C: 0.09% to 0.38%, Si: 0.05% to 2.0%, Mn: 0.5% to 3.0%, P: 0.05% or less, S: 0.05% or less, Al: 0.005% to 0.1%, N: 0.01% or less, Sb: 0.002% to 0.03%, and the balance being Fe and inevitable impurities, and having a tensile strength TS of 980 to 2,130 MPa.

Hot-pressed steel sheet member, steel sheet for hot-press, and method for manufacturing hot-pressed steel sheet member

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Tetsuo Yamamoto