Effect of graphene coating on mechanical properties of Cu-Ni interface in continuous casting mold

Abstract

Continuous casting is a process that can efficiently and economically produce a large amount of slab. However, since the mold for solidifying the liquid molten steel is exposed to high temperatures for a long period of time, flaking of the copper plate occurs occasionally as a result of local thermal stress concentration. Most of it occurs at the meniscus position on the upper part of the mold. In the past, flaking on the lower part of the mold used to be a problem, but it has not occurred yet through improvement of coating methods such as thermal spray and laser cladding. This flaking of the copper plate is fatal in the slab production process. Liquid molten steel may leak out of the facility, resulting in a break-out. Furthermore, if flaking is discovered, the mold must be replaced, which reduces productivity. We determined that the flaking was triggered by the Kirkendall effect caused by interface diffusion. To avoid interfacial diffusion and eliminate Kirkendall voids, a graphene layer was coated between the Cu and Ni of the mold copper plate. A graphene layer was produced using chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods, both of which are already in use in various other industries. Small specimens were made before testing on a large mold, and various mechanical properties were measured. The adhesion strength improved and the thermal properties were similar as a result of coating the graphene layer in the laboratory. These findings indicate that it is safe to add a graphene layer on a continuous casting mold of actual size in the future and apply it in the field.