Abstract
Transverse cracking in continuously cast microalloyed and low-alloyed steels has been shown to occur by a mechanism involving the formation of cavities at grain boundaries. Cavities are nucleated primarily at MnS and AIN particles. Crack formation by this mechanism can be minimized by encouraging stress relaxation away from grain boundaries and by avoiding the precipitation of sulphide and nitride particles on the grain boundaries. Gleeble testing has shown that the hot strength may be reduced and, therefore, the degree of stress relaxation improved, by minimizing alloying addition, particularly of Nb, V, and N in microalloyed steels and Cr, Ni, and Mo in low-alloy steels. Precipitation on grain boundaries may be reduced by additions of Ca and/or Ce or Ti and/or Zr, which cause the sulphides and nitrides, respectively, to precipitate in the liquid. Temperature cycling, particularly through the α–γ transformation, should also be avoided. The use of such measures has resulted in the production of C–Mn–Nb–Al slabs, > 300 mm thick, which do not require any surface dressing before rolling.
MST/51
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