An investigation of the cracking mechanism in continuous casting rolls during service.

摘要

A representative test, the Gleeble thermal and mechanical fatigue test, has been created to investigate the cracking mechanism in continuous casting rolls during service and to evaluate the overlay materials of the roll. In this Gleeble test, the thermal and mechanical conditions at the critical point of the roll, which is located at the middle point of the roll span and contacts the slab during stoppage of the caster operation, were simulated. The thermal and mechanical fatigue life and metallurgical evaluation were the criteria of the evaluation of the roll overlay materials. Two kinds of the overlay materials: A and B have been tested. The results well agree with practical evaluations.;In order to determine the thermal and mechanical conditions at the critical point, the finite element analysis was used to simulate the thermal and mechanical stress states in the entire roll for either steady or transient states, which includes both stoppage and restart periods. Both calculated temperature distributions in the roll and deflection of the roll have been compared with actual measurements.;The metallurgical study shows that cracking in the roll, generally, started from the surface of the roll and propagate into the overlay material. The occurrence of crack was not only found during service but also before service, i.e. after welding. The locations of the cracks were most likely at the bead to bead interface. With Electron Microscopy it was found that the grains were enlarged and the carbides of chromium and molybdenum were grown up and redistributed at the grain boundaries at the previous side of the bead to bead interface. Consequently, the grain boundaries were damaged through a loss in ductility balance between the grain to grain boundary, and cracks were more easily found. In addition, the coarse grain size and inclusions at the bead to bead interface also promoted fractures at this area.