Abstract
Fracture surfaces of the rolls have been examined with an electron microscope in relation to the size of cracks and bending stress at breakage, in order to have a technical aspect for the development of materials for slab mill roll. The results obtained are as follows:
1. The roll life is increased with the decrease of the proportion of the region of brittle fracture to the fracture surface.
2. The fatigue strength reduction factor of the slab mill rolls is smaller than 1.5, and the notch sensitivity of cast steels seems to be very small.
3. Following three types of fractures are found;
(1) fracture by fatigue crack initiated from heat crack.
(2) fracture by thermal stress.
(3) fracture originated at the inner defects introduced during casting.
(4) fracture originated at the inner defects introduced during overlay welding.
