Inclusion engineering through deoxidation practice optimization for enhanced mechanical properties of cast Cr-Ni-Mo steel

Abstract

Deoxidation is an integral part of steelmaking, as it determines steel castability, cleanliness, and porosity levels of the final product. Steel quality is critical to its performance and can be sabotaged by impurities such as non-metallic inclusions and porosity. This study investigates the effects of four distinct deoxidation practices, using Al, Al-Ca, Zr-Ca, and Mn-Si respectively, on tensile strength, tensile ductility and impact toughness of a Cr-Ni-Mo steel. These deoxidation reactions were modeled on a commercially available thermodynamic software and possible inclusion product phases were predicted. The casting samples were studied on a scanning electron microscope (SEM) utilizing energy dispersive X-ray spectroscopy (EDS) and an automated feature analysis program to determine the type, size, morphology and distribution of inclusions formed by the various deoxidation practices. The mechanical properties result showed that the Mn-Si killed casting produced the best strength of 257 ksi ultimate tensile strength and 196 ksi yield strength, while the Al-killed Ca-treated casting produced the best breaking energy of 34 J at −40C and 41 J at room temperature. However, the best elongation to failure (11.75 %) and area reduction (31.25 %) were recorded in the Zr-killed casting. These mechanical properties were correlated with the non-metallic inclusion parameters.