To provide a high-strength hot-rolled steel sheet suitable for structural members of large construction/industrial machinery.
A steel material, having a composition which includes 0.08-0.25% of C, 0.01-1.0% of Si, and 0.8-2.1% of Mn and in which the contents of P, S and Al are adjusted to appropriate ranges, is heated to a temperature of 1,100-1,250°C; subjected to rough rolling; subjected to finish rolling such that the value found by dividing the cumulative rolling-reduction rate in the partially recrystallized γ region and the non-recrystallized γ region by the cumulative rolling-reduction rate in the recrystallized γ region is 0-0.2; immediately cooled after completion of the finish rolling and cooled to a cooling stop temperature of Ms point +150°C or lower, within 30 seconds from the start of cooling at a cooling rate that is higher than or equal to the martensite-generating critical cooling rate in terms of average cooling rate within the temperature range of 750-500°C; kept for 5-60 seconds within the temperature range of ±100°C of the cooling stop temperature; and wound up into a coil shape at a winding temperature within the range of ±100°C of the cooling stop temperature. Thus, the hot-rolled steel sheet simultaneously having high strength and high toughness with yield strength YS of 960 MPa or higher and excellent bending characteristics is obtained.
YAMAZAKI KAZUHIKO
| JP2009263715A | 2009-11-12 | |||
| JP2010174280A | 2010-08-12 | |||
| JP2005314798A | 2005-11-10 |
| WO2012014926A1 | 2012-02-02 |
Eiichi Kobayashi
Suzuki Yoko
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