The effects of calcium treatment on stress relief cracking were investigated in Ni-free type HT80 steels. Calcium was added into molten steel in the fountains during bottom pouring. The y-groove restraint cracking test method was primarily used as stress relief cracking test.
As a result, stress relief cracking was remarkably reduced by calcium treatment and close correlation was observed between the susceptibility to stress relief cracking and the amount of free sulphur which was calculated by (Stotal-32/40Ca). The amount of free sulphur is considered to decrease by calcium treatment. This is explained mainly by the reason that stress relief crack tends to propagate along grain boundary as the surface energy of cavities in the grain boundary is decreased by the segregation of free sulphur.
