Low yield ratio high toughness thick steel plate excellent in low temperature impact toughness and method for producing the same

摘要

The present invention discloses a low yield ratio high tough tough steel plate having excellent low temperature impact toughness. The steel plate has a chemical element mass percentage content of C: 0.05 to 0.11%, Si: 0.00. 10 to 0.40%, Mn: 1.60 to 2.20%, S ≦ 0.003%, Cr: 0.20 to 0.70%, Mo: 0.20 to 0.80%, Nb: 0 0.02-0.06%, Ni: 3.60-5.50%, Ti: 0.01-0.05%, Al: 0.01-0.08%, 0 N ≦ 0.0060%, 0 O ≦ 0.0040%, 0 Ca ≦ 0.0045%, the balance being Fe and inevitable impurities; and Ni + Mn ≧ 5.5. The present invention further discloses a method for producing the steel sheet, which includes the steps of smelting, casting, heating, two-stage rolling, quenching, quenching after quenching, and tempering.