Abstract
Mechanism of breakage of hot work roll with high rolling load was analyzed on the basis of fracture mechanics. It was revealed that the process to the breakage of hot work roll could be represented as a cir cumferential fatigue crack growth from the fire crack to the critical depth, where stress intensity factor was equal to the fracture toughness of the roll material. Simulation of the circumferential fatigue crack growth was carried out on a continious billet mill roll using fatigue crack propagation properties (f.c.p.p.) of the roll material. The simulation results could explain the breakage pattern of the roll on actual rolling service, and made it clear that the life of hot work roll before breakage highly depended on the f.c.p.p. Test rolls (ultra high carbon steel roll) with superior f.c.p.p. were manufactured on the basis of the previous study made by the autors. From the performance results, it was found that resistance to breakage of the test rolls was remarkably improved and that the total rolling tonnage of the test rolls could be increased by 50% with the help of the improvement of wear due to the massive carbide which was intentionally intro duced for the improvement of f.c.p.p.
