| 摘要 |
The invention relates to a method for the production of a martensitic steel sheet having a yield point greater than 1300 MPa. The method comprises the following steps consisting in: supplying a semi-finished steel product having a composition containing, expressed as weight percent, 0.15% = C = 0.40%, 1.5%= Mn = 3%, 0.005% = Si = 2%, 0.005%= Al = 0.1%, S = 0.05%, P= 0.1%, 0.025%= Nb =0.1% and, optionally, 0.01% = Ti = 0.1%, 0% = Cr = 4%, 0% = Mo = 2%, 0.0005% = B = 0.005%, 0.0005% = Ca = 0.005%, the remainder of the composition being formed by iron and the inevitable impurities resulting from production; heating the semi-finished product to a temperature T1 between 1050�C and 1250�C and, subsequently, subjecting the heated semi-finished product to rough rolling at a temperature T2 between 1050 and 1150�C, with a cumulative reduction rate ea greater than 100%, such as to obtain a sheet having an austenitic structure that is not totally recrystallised, with an average grain size of less than 40 micrometres and preferably less than 5 micrometres; and cooling the sheet, such as to prevent the transformation of the austenite, at a rate VR1 greater than 2�C/s to a temperature T3 between 970�C and Ar3+30�C, and, subsequently, subjecting the cooled sheet to final hot rolling at temperature T3, with a cumulative reduction rate eb greater than 50%, such as to obtain a sheet that is then cooled at a rate VR2 above the critical cooling rate. |
