FIELD: metallurgy.
SUBSTANCE: invention relates to the field of metallurgy, namely to continuous production of martensitic steels processed on a continuous annealing line and used in the car industry. At least two first outer turns of a roll of a cold rolled steel sheet without thermal processing are unwound, including following elements, wt.%: 0.1≤C≤0.4, 0.2≤Mn≤2, 0.4≤Si≤2, 0.2≤Cr≤1, 0.01≤Al≤1, 0≤S≤0.09, 0≤P≤0.09, 0≤N≤0.09, if necessary, at least one element from: 0≤Ni≤1, 0≤Cu≤1, 0≤Mo≤0.1, 0≤Nb≤0.1, 0≤Ti≤0.1, 0≤V≤0.1, 0.0015≤B≤0.005, 0≤Sn≤0.1, 0≤Pb≤0.1, 0≤Sb≤0.1, 0≤Ca≤0.1, the rest is iron and unavoidable impurities. A front end of the unwound turn of the cold rolled steel sheet without thermal processing is prepared for welding and welded with the first longitudinal steel element having a carbon content lower than in the cold rolled sheet to obtain a welded cold rolled steel sheet. Then, the welded cold rolled steel sheet is wound up back, so that an unwelded end becomes an outer turn, and at least two first outer turns are unwound. The unwound end of the welded cold rolled steel sheet is prepared for welding, welded with the second longitudinal steel element having a carbon content lower than in the cold rolled sheet, and the welded cold rolled steel sheet is wound up to obtain a composite roll. Annealing is carried out by heating of the specified composite roll at a speed of more than 2°C/s to an exposure temperature between Ac3 and Ac3+100°c, and the roll is kept for 10-500 s, where the temperature Ac3 relates to the cold rolled steel sheet without thermal processing. Then, the composite roll is cooled at a speed of more than 25°C/s to a temperature lower than Ms value, and the composite roll is kept for a time between 10 and 1000 s in a temperature range between 150°C and 400°C, where Ms temperature relates to the cold rolled steel sheet without thermal processing. The composite roll is cooled to a room temperature, and a cutting operation is carried out for removal of the first longitudinal steel element and the second longitudinal steel element to obtain martensitic sheet steel.
EFFECT: obtainment of martensitic steels having required strength characteristics, using a continuous line of thermal processing.
16 cl, 7 dwg, 4 tbl
