Microstructure evolution of 423Co martensitic stainless steel coatings under thermal fatigue tests

This study evaluates the microstructural evolution of the 423Co martensitic stainless steel used as continuous casting rolls coatings, when submitted to thermal fatigue tests. The microstructural evolution was investigated through analysis by optical microscopy - OM, scanning and transmission electron microscopies - SEM and TEM, and X ray diffraction - XRD. Specimens were extracted from the Heat Affected Zone close to the interbead areas of the welded cladding. Tubular wires in a Submerged Arc Welding Process were used in this study. The results were interpreted according to the microstructural evolution of the cladding. Initially in the as-welded condition, heat-affected-zones presented fine lath martensitic microstructure with fine carbides. With the thermal fatigue test evolution the microstructure progressively deteriorated due to the tempered lath martensite formation and carbides growth until the failure of the material.