ArcelorMittal S.A.
Method for manufacturing a high strength steel product and steel product thereby obtained

Abstract:

A method for manufacturing a steel product includes providing a heated steel starting product at a temperature between 380.degree. C. and 700.degree. C., having a metastable fully austenitic structure, with a specified composition. Then the starting product is hot formed at a temperature between 700.degree. C. and 380.degree. C., with a cumulated strain .epsilon..sub.b between 0.1 and 0.7, in at least one location of the heated steel starting product, to obtain a fully austenitic hot-formed steel product; quenched by cooling the product down, at a cooling rate VR.sub.2 superior to the critical martensitic cooling rate, to a quenching temperature QT lower than Ms in order to obtain a structure containing between 40% and 90% of martensite, the rest of the structure being austenite; then maintained at, or reheated up to a holding temperature PT between QT and 470.degree. C. and holding the product at the temperature PT for a duration Pt between 5 s and 600 s.