Influence of Calcium Treatment and Electromagnetic Stirring on Ridging in Dual-Stabilized Ferritic Stainless Steels

Titanium and niobium are added to ferritic stainless steels (FSS) to enhance their surface and mechanical properties. The use of titanium to obtain FSS sheets that are resistant to ridging due to the formation of equiaxed rather than columnar grains during solidification is well established. However, the use of titanium results in clogging the submerged entry nozzle during casting, causing surface defects in cold-rolled products and overall production losses. To overcome the clogging problem, calcium treatment is conducted in the ladle furnace to transform inclusions into the liquid state. However, this delays the formation of the TiN inclusions which act as nuclei for the equiaxed grains, thereby increasing the fraction of columnar grains in the slabs and susceptibility to ridging in the final cold-rolled and annealed product. Herein, the effect of calcium treatment and electromagnetic stirring (EMS) on the equiaxed grain ratio and ridging is studied with industrially produced material. The beneficial effect of EMS on grain structure and ridging is largely lost at high calcium contents, but it can be retained, provided the level of calcium is maintained at a sufficiently low, optimum level.