Study of impurities in newly manufacturing 1215MS+Bi steels by altering cooling processes

Abstract

ABSTRACT To accurately study the distribution characteristics of impurities and microstructures in the 2800 ppm Bi content 1215 MS steel, the horizontal solidification experiments were carried out by altering horizontal cooling processes. Results show that under moving rates (υ) = 0.3 mm/s and 0.5 mm/s the equivalent diameters of the impurities in steels at the interface between the chilled grain zone and columnar grain zone were higher at 1.6 ~ 1.8 μm, 2 ~ 3 times larger than those in the chilled boundary. Most small-sized inclusions were gathered in circular or linear distribution with the sizes of <1.0 μm. The morphologies of MnS/Bi-MnS inclusions were in rod-like, long strip, spindle, ellipsoidal, and spherical shape. The high υ value was beneficial for increasing the equivalent diameters of the impurities in the chilled grain zone and resulted in the reduction in the inclusions sizes in the columnar grain zone but it seldomly affected their sizes in the equiaxed grain zone. The morphologies of the equiaxed grains were in directional stacking, cross, anisotropy and coniferous pine types.