Influence of calcium treatment on cleanness and fatigue life of 60Si2MnA spring steel

摘要

Contrasting experiments of Al killed 60Si2MnA spring steel were carried out between using and excluding calcium treatment under LF refining slags with low and high basicity ratios (R: CaO/SiO2 = 3.4, 5.0), respectively. Results showed the high basicity refining slag had a certain effect on controlling inclusions and improving the cleanness of spring steel similarly to calcium treatment. The T.[O] (total oxygen) content of steel without calcium treatment got to below 15 ppm and the fatigue life was long, up to 7.8 x 10(6) cycles. But in order to reduce the T.[O] below 10 ppm, as well as inclusion number and size in spring steel further, meanwhile, the appropriate calcium treatment should still be used. Besides, as the [Ca] content in the steel with calcium treatment increased, inclusions transformed from Al2O3-SiO2-CaO-MgO to Al2O3-SiO2-CaO-MgO-CaS completely, which reduced the formations of voids between inclusions and steel matrix, and voids decreased with the increase of CaO/Al2O3 value and CaS content of inclusions. Finally, the fatigue life of spring steel with high basicity slag and calcium treatment increased to 9.1 x 10(6) cycles.