Abstract
An adamite work roll used in the hot strip finishing mill was examined to investigate the banding of work roll. Defects observed on the roll surface are heat cracks, pits and shallow hollows. The banded surface is dense aggregation of pits and shallow hollows.
Heat cracks are observed at all roll surface and they are about 100-200μdeep. It is ascertained from their fracture surface that they are formed by thermal fatigue.
Pits are about 100-120μ deep and it is considered that heat cracks and large cementites cause the local crumbling which develops into pits.
Shallow hollows are observed only in the banding zone and moreover the greater parts of the banding zone are occupied by them. They are about 0.2-0.5mm wide, 0.5-2.0mm long and less than 20μ deep. The observation by electron scanning microscope shows that they are formed by the abrasion by hard substances. It is suggested from the hardness measurements at high temperature that large cementites in the roll and magnetites in the scales of hot strips may be abrasive substances.
Scales on the surface and in the cracks are studied by X-ray diffraction and electron probe microanalyser. The scale on the surface are considered to be attached ones from hot strips and these in the cracks are considered to be oxides of the roll material.
