Metallurgical characteristics of electroslag-refined MDN 250 maraging steel

Abstract

MDN-250 maraging steel was electroslag-refined in a 350 kVA DC ESR unit using a slag of composition, CaF₂-65, CaO-9, Al₂O₃-2O, TiO₂-5, and MoO₃-1 (wt % basis) in straight as well as reverse polarity modes of melting. The chemical homogeneity of the ingots was established by X-ray fluorescence, plasma scan and spectrovac methods. The dissolved gas content (O and N) in the ingots was determined by a LECO gas analyser. Volume fraction, density and size distribution of inclusions in the ingots and the electrode were determined in a Quantimet image analyser. These results were supplemented by EPMA and SEM studies on selected inclusions. Mechanical properties of the ingots in the heat-treated and aged conditions were assessed and compared with those of the electrode material.

The present results confirm that the reverse polarity mode of melting is best suited for producing quality maraging steels for the ingots produced by this mode of melting were found to possess superior metallurgical characteristics in terms of cleanliness and mechanical properties compared to those produced by the straight polarity ESR route and other conventional methods.