A Study on Crystallinity of Mold Fluxes for Continuous Casting of Peritectic Steel.

Over 90% of the steel produced in the world is cast via continuous casting route. Bulk of this steel, belongs to peritectic grade having carbon content ranging between 0.1 to 0.5 %. The peritectic reaction is associated with volume contraction during α-ferrite to austenite transformation which is considered to be the root cause of the stresses evolved during solidification of casting leading to the appearance of longitudinal cracks, which is a matter of concern. It is known that the controlled rate of horizontal heat transfer minimizes the thickness of steel shell which is able to bear contraction stresses, reducing thereby the tendency of formation longitudinal crack. This is achieved by allowing to form thicker layer of solidified flux, between the mold and the strand, with higher fraction of crystalline phase. In the light of this, X-Ray Diffraction and Metallographic techniques were established to determine fraction of crystalline phase in fluxes. The fluxes were decarbed, melted and quickly solidified. Due to fast cooling samples were almost in glassy state. Glassy to crystalline transformation was then carried out isothermally at temperatures between 700°C to 1000°C and for a time period of 2 to 6hrs. Fraction of crystalline phase was determined in all the three fluxes as a function of temperature and time. Based on these studies, attempt has been made to explain the behavior of the fluxes in the context of formation of longitudinal cracks.