| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a high-strength and high-toughness steel plate excellent in the strength and deformability in a middle temperature zone, especially suitable to use for welded steel tube for steam-piping. SOLUTION: The steel composed, by mass, of 0.05-0.08% C, 0.05-0.2% Si, 1.6-2% Mn,≤0.02% P,≤0.002% S, 0.05-0.3% Mo, 0.03-0.07% Nb,≤0.02% Ti,≤0.04% Al,≤0.015% REM,≤0.006% N and the balance Fe with inevitable impurities and satisfying≥0.025% Nb<SB>eff</SB>in the formula, Nb<SB>eff</SB>=0.002×(1-25Ti)/(C+0.86N) (wherein, Ti, C, N are mass% in each element) is hot-rolled at≥50% accumulated rolling reduction ratio at≤900°C after heating, and at≤850°C rolling finish temperature and thereafter, this hot-rolled steel is cooled till >550°C to≤650°C at≥5°C/sec cooling speed and immediately, reheated to 610-720°C at≥0.5°C/sec temperature raising speed. COPYRIGHT: (C)2007,JPO&INPIT
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