A -CASE STUDY OF THE INFLUENCE OF DEOXIDATION PRACTICE ON THE MORPHOLOGY AND CHARACTER OF NON -METALLIC INCLUSIONS IN CERTAIN GRADES OF STEELS

Abstract

A study of eight different grades of steels obtained from M/S U.P. Steels, Muzaffarnagar, has been made with a view .to ascertaining the influence of deoxidation practice on the cleanliness levels of these steels. Specimens were drawn at different stages of the processing of above heats. These stages. were : after melt-out, after refining (carbon boil), after reducing period and from the ladle. The morphology, volume fraction and approximate chemical composition of inclusions was ascertained with the help of optical, quantitative *metallographic SEN and EPMA techniques respectively. It was found that the volume fraction of inclusions is fairly high during melt out and refining period and then their number decreases after the reducing period and in the ladle. The inclusions found at the melt out and refining stage usually conform to FeO-MnO-Al203 system and many times, the inclusions are only FeO. Because of alloy additions and deoxidation during reducing period, the composition of inclusions becomes very complex. Many times, the inclusions contain FeS-MnS-CaS, which must be slag inclusions. Indigenous inclusions formed due to deoxidation practice usually contain CaO-A1203-MnO-FeO. The inclusions found in the ladle sample were usually globular in shape and of very fine size (5-8 um). But some eroded refractory pieces were also found in this specimen, which had reacted with the steel. Present studies revealed that some grades of steels manufactured by LN1/S U.P. Steels did show fairly low volume fraction •of NMIs in the ladle, while others did show much higher volume fraction of non-metallic inclusions in the ladle. This signified that the steel making practice of the above works was not very consistent.