MARTENSITIC STEEL WITH DELAYED FRACTURE RESISTANCE AND MANUFACTURING METHOD

摘要

A cold rolled and annealed martensitic steel sheet is provided. The steel sheet includes by weight percent, 0.30≦C≦0.5%, 0.2≦Mn≦1.5%, 0.5≦Si≦3.0%, 0.02≦Ti≦0.05%, 0.001≦N≦0.008%, 0.0010≦B≦0.0030%, 0.01≦Nb≦0.1%, 0.2≦Cr≦2.0%, P≦0.02%, S≦0.005%, Al≦1%, Mo≦1% and Ni≦0.5%. The remainder of the composition includes iron and unavoidable impurities resulting from melting. The microstructure is 100% martensitic and a prior austenite grain size is lower than 20 μm. The steel sheet has a delayed fracture resistance of at least 24 hours during an acid immersion U-bend test. A method, part, structural member and vehicle are also provided.

主权项

1. A cold rolled and annealed martensitic steel sheet comprising, by weight percent:
0.30≦C≦0.5%; 0.2≦Mn≦1.5%; 0.5≦Si≦3.0%; 0.02≦Ti≦0.05%; 0.001≦N≦0.008%; 0.0010≦B≦0.0030%; 0.01≦Nb≦0.1%; 0.2≦Cr≦2.0%; P≦0.02%; S≦0.005%; Al≦1%; Mo≦1%; and Ni≦0.5%; the remainder of the composition being iron and unavoidable impurities resulting from melting; the microstructure being 100% martensitic with a prior austenite grain size lower than 20 μm; and the steel sheet having a delayed fracture resistance of at least 24 hours during an acid immersion U-bend test.