Control of sulphur and minimisation of centre line segregation for Rail Steel

Abstract

Rail is the most important constituent of the track structure and plays a very vital role in the reliability of railway system as a whole. Quality of rail steel with reference to its chemical composition has been a matter of prime importance for the manufacturers as well as Railways. Sulphur is a detrimental element in rails since it causes hot shortness during rolling, centerline segregation during casting, poor weldability for the rails etc. To improve quality of rails, a substantially low range of sulphur < 0.015% (Railway's specified norms <0.03%) has been targeted in Bhilai Steel Plant by adequate sulphur control measures in steelmaking process. A two stage desulphurisation treatment is now employed in which the blast furnace hot metal is first treated by co-injection of Mg and CaC reagents, and subsequent treatment with a 2 synthetic slag former (CaO-Al O ) added to the ladle during tapping from the Basic 2 3 Oxygen furnace. Improvement in the internal quality of the cast bloom has been established by introduction of Electro Magnetic Stirring. The centerline segregation is minimized vis-a-vis the properties of the cast product and rails improved by the successful implementation of step by step control measures.