| 摘要 |
A method for producing a high strength coated steel sheet having a yield strength YS of at least 800 MPa, a tensile strength TS of > 1 180 MPa, a total elongation > 14% and a hole expansion ratio HER > 30%. The steel contains in weight %: 0.13%≤ C ≤ 0.22%, 1.2% ≤ Si ≤ 1.8%, 1.8% ≤ Mn ≤ 2.2%, 0.10% ≤ Mo ≤ 0.20%, Nb ≤ 0.05%, Al ≤ 0.5%, the remainder being Fe and unavoidable impurities. The sheet is annealed at a temperature TA higher than Ac3 but less than 1000°C for more than 30 s, then quenched by cooling temperature QT between 325°C and 375°C,at a cooling speed sufficient to obtain a structure consisting of austenite and at least 60% of martensite, the austenite content being such that the final structure can contain between 3% and 15% of residual austenite and between 85 and 97% of the sum of martensite and bainite, without ferrite, then heated to a partitioning temperature PT between 430 °C and 480 °C and maintained at this temperature for a partitioning time Pt between 10 s and 90 s, then hot dip coated cooled to the room temperature. Coated sheet obtained. |
