Method of producing martensite-or bainite-rich steel using steckel mill and controlled cooling

An in-line method for producing a rolled steel product, including continuously casting a strand of steel, severing the cast strand transversely into a series of slabs, reheating the slabs to a substantially uniform pre-rolling temperature, and reversingly reduction-rolling the reheated steel slabs;

• characterized by:
• (a) applying to the cast steel an upstream quench prior to reheating so as to quench a surface layer of the cast steel to a selected depth so that the surface layer is transformed from an austentitic to a substantially non-austentitic microstructure;
• (b) shearing the leading edge of the rolled steel immediately after completion of rolling to crop the steel so as to provide a precise transverse vertical face on the leading edge of the rolled steel;
• and
• (c) applying to the cropped rolled steel a controlled temperature reduction so as to obtain a microstructure of the steel that includes a substantial portion of bainite or a substantial portion of martensite;
• and further characterized in that
• (d) the slabs are reheated to a suitable pre-rolling temperature above the temperature Tnr sufficient to transform the quenched surface layer to fine-grained austenite;
• and
• (e) the slabs are reduction rolled first in a temperature range above the temperature Tnr and then at a decreasing temperature between the temperatures Tnr and Ar3 to obtain first a controlled recrystallization of austenite and then a pancaking or flattening of the austenite grains.