Formation Mechanism, Evolution and Modification of Non-Metallic Inclusions in Al-killed, Ti-Alloyed Steel Melt: A Review

Titanium alloying is done to impart special properties to the steel. Addition of titanium to an Al-killed steel results in the formation of transient Al-Ti-O inclusions. These Al-Ti-O inclusions cause castability issues and enhance the nozzle clogging phenomenon during continuous casting. The present study comprehensively reviews the formation mechanism, evolution, and modification of Al-Ti-O inclusions during secondary steelmaking covering simple (Al and Ti) and complex (Al-Ti) deoxidation equilibria. The formation mechanism of transient Al-(Mg)-Ti-O inclusions in Al-killed, Ti-alloyed steel has also been discussed in detail. The influence of important process parameters such as the addition sequence of Ti, its sources (Ti/ferrotitanium type), the presence of Mg and the Ca treatment for the modification of Al-Ti-O have been covered. In a nutshell, we have endeavoured (a) to link the various stages from the formation to modification via the transient route of Al-Ti-O inclusions and (b) to identify the gaps which are not clearly established and/or not understood. Bridging these gaps could be an effective approach to enhance steel cleanness in Al-killed, Ti-alloyed steel grades.