Failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting. Part I: Material and fractographic characterization

摘要

The failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting and used in cast glass rolling was carried out by means of traditional characterization techniques (optical metallography, SEM, EDX microanalysis, tensile testing and XRD). The roll was in the as-cast condition and its microstructure featured large proportion of δ ferrite (between 20% and 27%) in a martensitic (α') matrix, with the δ/α' interfaces presenting an intergranular network of M_(23)C_6 carbides. The crack propagation began in the internal surface of the roll, with δ/α' intergranular and transgranular cleavage in the "equi-axed region" of the casting, progressing to δ/α' intergranular ductile fracture in the "columnar" and "chilled regions". Tensile thermal stresses in the internal surface of the roll associated with microstructural embrittlement (network of interfacial carbide and micro-porosities) are thought to be the main causes for the premature failure of the roll. Finally, materials selection was performed to replace the CA-15M stainless steel with another class of stainless steel for centrifugal casting.