Improvement in Castability of Al-Killed Steel in Billet Casters by Process Optimization

Abstract

Sticking of alumina as well as spinel inclusions inside the sub-entry nozzles as well as tundish nozzle is a perennial problem during continuous casting of aluminum-killed steel through billet casters. This results in restriction or complete blockage of flow of liquid steel through the nozzles eventually leading to abortion of sequence in billet casters and stopping of continuous casting machine. Nozzle clogging not only restricts the productivity by restraining the casting sequence, intermittent extrication of clogged alumina particles or dislodged refractory materials which are a significant source of non-metallic macro-inclusions in the cast sections of billet casters. If these inclusions are not removed completely during secondary refining of steel, they cause excessive clogging mainly in low-carbon Al-killed steels. In other grades of Al-killed steel, clogging is also very prominent if the deoxidation and secondary refining is not carried out properly. IISCO Steel Plant (ISP), Burnpur, a new, modernized unit of Steel Authority of India Limited, was facing problems of nozzle clogging in low-carbon, low-Si, Al-killed grade (EWNR—electrode quality grade) resulting in premature abortion of casting sequence leading to huge productivity loss. To solve the problem of nozzle clogging in low-carbon Al-killed grades and other grades at ISP, optimization of various steelmaking parameters, viz., amount of Al addition and its sequence, purging regime in ladle furnace, optimization of Ca treatment process, etc. has been carried out which has resulted in improvement in castability of Al-killed steel in billet caster of ISP.