Effect of Thermo-mechanical History on Surface Cracking of As-cast Low Carbon Low Alloy Steel Slabs

Surface cracking and the effect of predeformation on the cracks of low alloy steel slabs in the continuous casting and the direct rolling processes have been studied by means of hot bending tests simulating the processes using as-cast thin slabs. Two kinds of cracks, i.e., fine transverse cracks in microalloyed steels and severe cracks in low Mn steels, are easily simulated by the deformation in low temperature γ region, if the deformation conditions are suitably controlled. They are markedly suppressed by the slight predeformation at certain conditions on the slab surface during cooling to the bending temperature. These results can consistently be explained in terms of precipitation behavior of carbonitride or sulfide. Suppression of the cracks due to the predeformation is caused by nucleation and coarsening of the precipitates by the deformation, and does not result from γ grain refinement by recrystallization due to the predeformation.