Production of DMR 249A Steel at SAIL, Bokaro Steel Plant

Abstract

Low alloy steels are an attractive option for high performance structural applications due to cost and availability factors. A low carbon low alloyed steel, DMR 249A, was developed for strategic applications by Indian Navy at Steel Melting Shop II, Bokaro Steel Plant (SMS II, BSL). This paper enumerates the detail process variables modified for this development. DMR 249A grade was having the specified gas contents of hydrogen <2 ppm in final product for the avoidance of detrimental phenomenon like “Hair Line Cracks”. So the Hydrogen content of liquid steel was to be less than 3 ppm and this demand vacuum treatment of the steel. In absence of any Degassing unit at SMS II, BSL, making of DMR 249A steel was a challenging task. The hydrogen content of steel was controlled through restriction of hydrogen in input raw materials, control in degree of deoxidation during tapping, slag basicity at ladle furnace, argon rinsing regime and cooling of slabs i.e. control over diffusion of H2. The steel was produced with the existing infrastructure at Bokaro Steel Plant with various alloying elements and processed suitably to obtain the desired yield strength, toughness and gaseous content. The control was exercised at various stages of steel making and hot strip rolling to enable achievement of a higher degree of consistency in mechanical properties and microstructure. Quality fulfillment was a great challenge without vacuum degasser unit but Bokaro successfully made the steel with 100% customer satisfaction.