| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a method for producing, at high producing efficiency and at a low cost, a low yield ratio, high strength and high toughness steel plate excellent in a weld heat-affected zone toughness having high toughness at a portion including the welding heat-affected part. <P>SOLUTION: The method for producing the low yield ratio and high strength steel plate excellent in the weld heat-affected zone toughness is characterized in that the steel containing, by mass%, 0.03-0.1% C, 0.01-0.5% Si, 1.2-2.5% Mn,≤0.08% Al, 0.008-0.025% Ti and 0.004-0.007% N wherein Ti/N being the ratio of Ti content and N content is 2-4 is hot-rolled at rolling finish temperature higher than Ar<SB>3</SB>temperature to form the steel plate, then the steel plate is subjected to accelerating cooling to 450-650°C at≥5°C/s cooling speed and immediately thereafter, is reheated to 550-750°C at≥0.5°C/s temperature rise rate, so that the metallurgical structure in the steel plate is substantially changed to three phase structure of ferrite, bainite and isolated martensite whose partial area ratio is set to 3-20%. <P>COPYRIGHT: (C)2005,JPO&NCIPI</p> |
