Procedures to evaluate roll overlay for the continuous casting of steel

Since the mind 1960's, the thermal, corrosive and mechanical loading of support, guide and withdrawal rolls in continuous steel casters has been getting greater and greater. The support, guide and withdrawal rolls of many continuous slab casters have to be removed after throughput quantities of about 600,000 tons and repaired, renewed or replaced. This entails considerable costs for caster operators. In order to avoid roll wear as a consequence of the increased roll loading, the rolls are being coated with materials which have a distinctly higher wear resistance than the base roll materials. In continuous castings, the wear-resistant overlay coatings are subject to cyclic thermomechanical stresses, raised temperatures, and an adverse environment. Recent roll development projects conducted by roll manufacturers primarily were initiated to determine the optimum overlay material, chemical composition of the alloy groups effective and economic overlay welding processes and procedures, and meaningful roll evaluation testing methods. In this project the researchers at the Ohio State University have developed a quantitative material evaluation test which simulates the critical cyclic stress and thermal conditions, which the roll overlay material experiences during castings. This evaluation method consists of an integrated approach, which includes finite element analysis and Gleeble test. The OSU roll evaluation method has been used to evaluate three types of overlay materials each with distinct metallurgical properties. The test result show consistent life cycles for each metallurgical type and a clear difference In the life cycle magnitude among the three types. In summary, this project resulted in the development of a quantitative test for evaluating the overlay materials of the continuous castings rolls. To improve the strength and ductility of the roll overlay, controlled welding heat input is recommended to reduce grain coarsening and carbide precipitation and growth at the grain boundaries. Precautions are also recommended with regard to welding procedures and workmanship in order to minimize microinclusions at the weld bead interfaces.