A fundamental study on life assessment of continuous slab casting rolls

In the continuous slab casting process, the caster roll life is the major factor which controls and limits steel productivity. Due to the heavy loading and harsh environments, the rolls have to be resurfaced or replaced after certain amounts of tonnage. This entails considerable costs. To extend service life, rolls are cladded with materials that have a distinctly higher wear and cracking resistance than the base roll materials. Weld overlay materials are generally selected either by simple tests performed by roll manufacturers or by long term trials on the actual caster machines. The former test does not realistically reflect the loading and environmental conditions, and the latter test is costly and time consuming. Therefore, understanding the roll overlay deterioration mechanisms, and studying the roll life by an effective evaluation method are of great significance and interest.; In this study the evaluation method consisted of three parts: the finite element analysis (FEA), simulation tests (fatigue test and wear test), and metallographic analysis. The FEA was used to determine the temperature and stress history of caster rolls when they were operating. Simulation tests were used to assess fatigue life and wear life under the thermal and mechanical stresses and to establish an optimum balance between fatigue life and wear life for the 12%-Cr overlay alloys. Metallographic analysis concentrated on understanding the roll deterioration mechanisms in casting service, and assessing the metallurgical causes for different fatigue life experimentally observed among samples.; The results obtained in this study showed that surface strain notches must have existed before fatigue cracking occurred. These notches were mainly caused by mechanical smearing, thermal shock, pit corrosion, and wear phenomenon at the roll/slab interface at elevated temperature. Circumferential fatigue cracks initiated from these notches. The cracks then propagated into the roll body driven by repeated thermal-mechanical longitudinal stresses. The roll surface was worn out gradually through spalling or delamination by combinations of abrasive, adhesive, and corrosion wear.; The roll life is controlled by either cracking or wear resistance depending on the overlay hardness. The softer roll overlay materials have longer fatigue lives but shorter wear lives. These data are useful for helping casters to predict the roll life under the operating conditions.