The Use of Direct Reduced Iron in Electroslag Processing, Furnace Equipment Design, and Transient Development of Molten Slag-Metal Systems

There is a growing demand for virgin steel worldwide and a need to revamp US industrial capacity to economically produce near net shape metal components (NNSMC) domestically. Electroslag strip cladding (ESC) and submerged arc (SAW) are direct energy deposition (DED) processes with two distinct phases (slag and metal) and are promising methods for additive manufacturing utilizing minimally refined low-cost feedstocks which have significant amounts of nonmetallic material. A review of ES history with a focus on the history of the use of direct reduced iron (DRI) as a feedstock in electroslag (ES) processes is presented. The equilibrium elemental constitution of gas-slag-metal systems can be calculated with high accuracy, but the transient element transfer and other transient phenomena in many metallurgical processes are notoriously difficult to model and study due to sensitivity of short time scale experiments and challenges in dealing with temperatures over 1400°C. Custom equipment was developed to enable programable thermo-physical simulations at high temperatures and extreme ramp rates for discontinuous solid and liquid samples weighing several grams. Small-scale samples were subjected to controlled time-temperature (t-T) profiles in simplified thermophysical simulations to probe the short time scale behavior of granular DRI, alloying ingredients, and welding flux feedstocks. Gas porosity, nonmetallic area ratio, nonmetallic inclusion quantity, and elemental homogenization of Fe increased with increasing assessed time and temperature. Nonmetallic inclusions in S415 were generally smaller, more prevalent, and comprised a smaller area ratio than in raw iron. Heating experiments resulted in the production of raw iron and S415-like stainless steel for time (in the molten state) ranging from ~15 s to ~120 s at temperatures ranging from ~1600°C to ~1800°C. These experiments correlate gas porosity, inclusion statistics, and elemental homogeneity of transient melting of DRI based iron and steel production. Results indicate that thermophysical simulations with a high degree of controllability is achievable for samples weighing several grams and that the production of raw iron and high alloyed steels is achievable in small-scale molten slag-metal systems relevant to ES time and temperature ranges.