Method for producing lutra-high-strength martensitic cold-rolled steel sheet by ultra rapid heating process

A method for producing ultra-high-strength martensitic cold-rolled steel, sheet via an ultra-rapid heating process, comprising the steps of

• (1) smelting and solidification of steel:
• steelmaking by converter, electric furnace or induction furnace, production of ingot by continuous casting to produce slab or die casting;
• (2) hot rolling after slab casting or ingot casting:
• the slab or ingot obtained in step (1) is heated by 1050-1250° C., and rolled by rough rolling mill and hot strip rolling mill to 2.5-15 mm thickness, batched at 500-700° C.;
• (3) subjecting the continuous hot-rolled strip obtained after the coiling in step (2) to pickling treatment, and then directly subjected to cold rolling to 0.5-2 min at room temperature;
• and
• (4) subjecting the cold-rolled steel sheet obtained in the step (3) to an ultra-rapid heating process, heating the cold-rolled steel sheet to 300-500° C. at a heating rate of 1-10° C./s, and then reheating at a heating rate of 100-500° C./s to austenite single-phase zone 850-950° C., after that, the steel plate is water-cooled immediately after the heat less than 5 s, then the ultra-high strength cold-rolled steel plate is obtained.