To reduce the thermal crown to lower than the case of the conventional complex roll and to secure the flatness of a plate to high level by weld- forming an outer layer on the outer periphery of shaft material having a specific thermal expansion coefficient and thermal conductivity by a continuous build-up welding.
In the complex roll used for a work roll in a hot-rolling finish mill, the raising of temp. of the shaft material is ordinarily within 100°C and the thermal crown is low and therefore, the trouble in the plate-passing is not caused. The thermal expansion coefficient of the shaft material at the room temp. -100°C is limited to ≤12×10-6/°C so that the thermal crown achieves the same or lower in comparison with an Ni grain roll composed of a ductile cast iron in the inner layer. Further, since the lower the thermal conductivity of the shaft material is, the lower the temp. raising of the shaft material is, and the thermal expansion accompanied with this lower temp. raising is restrained, and the thermal conductivity of the shaft material at the room temp. -100°C is made to ≤0.12cal/cm.sec.°C. Then, as the shaft material, SUS material, SK material, etc., excellent in low thermal expansibility, low thermal conductivity and mechanical properties is prefered.
MATSUNAGA EIHACHIROU
FURUSHIMA SEISHI
