high strength and high toughness steel plate and a method of manufacturing the same yield strength is 700MPa class

摘要

The present invention relates to a high-strength high-toughness steel plate, which contains the following chemical compositions, by weight, C: 0.03-0.06%, Si‰¤0.30%, Mn: 1.0-1.5%, P ‰¤0.020%, S‰¤0.010%, Al: 0.02-0.05%, Ti: 0.005-0.025%, N‰¤0.006%, Ca‰¤0.005%, and more than one of Cr‰¤0.75%, Ni‰¤0.40%, Mo‰¤0.30%, other compositions being Ferrum and unavoidable impurities. The manufacturing method thereof includes: after vacuum degassing treatment, continuous-casting or die-casting molten steel, and if the molten steel is die-casted, blooming it into a billet; heating the continuous casting slab or billet at temperature of 1100-1250°C, then one-pass or multi-pass rolling it in austenite recrystallization zone, with the total reduction ratio being ‰¥70% and the rolling finishing temperature being ‰¥860°C; water-cooling rapidly the rolled steel plate at speed of 15-50°C/s to the temperature 200-300 °C, then air-cooling it for 5-60s; after the cooled steel plate entering an online heating furnace, rapidly heating it at speed of 1-10°C/s to 450-550°C, tempering it for 15-45s, then air-cooling it outside the furnace. The finished steel plate with a thickness of 6-25mm has a yield strength of ‰¥700MPa, an elongation A 50 of‰¥18%, A kv at -60°C of ‰¥150J and good cool bending property, appropriately applied to industries of automobiles, engineering machinery and warship hull structures.