The double layer steel which is superior in the strength - ductile balance which does not have boundary exfoliation break and necking break

摘要

P To provide a multi-layer steel free from interfacial peeling fracture and necking fracture and having an excellent balance in strength-ductility. PSOLUTION: In the multi-layer steel in which a first layer composed of a steel essentially consisting of an austenitic structure or a ferritic structure and having a tensile strength TSSB1/SBof 1,200 MPa and a second layer composed of a steel essentially consisting of a martensitic structure and having a tensile strength TSSB2/SBof 1,200 MPa are stacked via an Ni alloy layer, and, with the first layer as the surface layer and three or more layers (other than Ni foil) are stacked and integrated and an Ni alloy layer whose Vickers hardness (Hv) in the central part of the sheet thickness direction is ≥ 150 and also an Fe content is 10 to 98 mass% is formed between the first layer and the second layer. PCOPYRIGHT: (C)2010 and JPO& INPIT