The Experimental Characterization and Numerical Simulation of A-Segregates in 27SiMn Steel

A 500-kg 27SiMn steel ingot has been produced via low-oxygen purifying technology and then fully dissected in the longitudinal center plane to investigate the typical features and formation mechanism of A-segregates. The macrostructure, microstructure, inclusions, cavity and solute segregation surrounding the A-segregates were characterized and analyzed in detail. It shows that the main solute components such as C, Si, and Mn, and even some large cavities accumulate obviously within the A-type channels. Owing to the low content of oxygen and other impurities, there is no apparent enrichment of the inclusions. Based on the classical theory of macrosegregation, driven by thermo-solutal buoyancy, A-segregates in the body of a 27SiMn steel ingot have been simulated successfully by using the multi-component continuum model. They disappear in a referred 1045 steel ingot. By comparing the evolution processes during solidification of both steels, it is demonstrated that the strong thermo-solutal convection originated from the high content of Si element in 27SiMn steel destabilizes the mushy zone and therefore induces the A-segregates. In terms of the occurrence zones of A-segregates and corresponding distributions of Rayleigh number, its critical value to predict the A-segregates in industrial steel ingots was proposed and then applied successfully.