PURPOSE: To prevent the generation of a crack and to reduce the cost of the rolling material from the improved yield by controlling the surface temp. of a continuously cast steel ingot of a low alloy steel specified in the range of C equiv. within the specific width at the end of the ingot in the direct hot rolling of said steel ingot.
CONSTITUTION: The continuously cast low alloy ingot of which the equiv. value [CP] expressed by formula I taking weight % of alloy elements Mn, Ni, Cu, N to sharply affect the peritectic point for generating the γ phase in the solidifying stage of the molten metal into account is 0.13W0.23 and with which the crack is liable to arise during rolling by the coarsening of the γ phase is delayed in cooling within the 50W200mm range from the ingot end by the influence of the molten steel discharge flow and is liable to have the coarsened γ phase in the case of subjecting such steel ingot to the direct hot rolling. The temp. within 200mm from the ingot end is consequently heated by a heater to ≥900°C or cooled by water down to ≤700°C and the steel ingot is rolled without having the time allowance for the coarsening of the γphase. The generation of the crack is thereby obviated and the yield is improved, by which the cost of the rolling material is reduced.
KAWASAKI MORIO
MAEHARA YASUHIRO
FUNAKI HIROYUKI
YOSHIHARA KAKUJI
MISHIMA TAKESHI
