HIGH-STRENGTH AND HIGH-TOUGHNESS STEEL PLATE WITH YIELD STRENGTH BEING 700 MPA AND MANUFACTURING METHOD THEREOF

摘要

A high-strength and high-toughness steel plate comprises components of, by weight: C (0.03-0.06%), Si (less than or equal to 0.30%), Mn (1.0-1.5%), P (less than or equal to 0.020%), S (less than or equal to 0.010%), Al (0.02-0.05%), Ti (0.005-0.025%), N (less than or equal to 0.006%), Ca (less than or equal to 0.005%), and more than one of Cr (less than or equal to 0.75%), Ni (less than or equal to 0.40%) and Mo ((less than or equal to 0.30%), and the residual being Fe and inevitable impurities. A manufacturing method thereof comprises: performing continuous casting or die casting on molten iron after vacuum degassing, and performing blooming after the die casting to form a billet; heating a continuous casting billet or the billet at 1100-1250°C and performing one-pass or multi-pass rolling on the heated continuous casting billet or billet at an austenite re-crystallization zone, a total reduction rate being equal to or greater than 70%, a final rolling temperature being equal to or greater than 860°C; a rolled steel plate being water-cooled to 200-300°C rapidly at a speed of 15-50°C/s, and being air-cooled for 5-60s; the cooled steel plate entering an online reheating furnace to be heated to 450-550°C rapidly at a speed of -10°C/s, tempering for 15-45s, and being taken out of the furnace for air-cooling. The obtained steel plate as thick as 6-25 mm has yield strength equal to or greater than 700MPa, elongation A50 equal to or greater than 18%, and Akv at -60°C equal to or greater than 150J, thereby being applicable to industries such as automobiles, engineering machinery and naval ship structures.