Formation and Control of CaS Inclusion in Gear Steel 20MnCr5

The modification of (CaO)m(Al2O3)n inclusion and the fact of CaS inclusion formation in gear steel 20MnCr5 after calcium treatment have been studied by thermodynamic equilibrium calculation. Based on the thermodynamic equilibrium, when the liquid steel containing 0.035% [Al], the mass fraction of sulfur is lower than 0.00628% and the ratio of w(Ca)/w(Al) is higher than 0.483, the lower melting point 12(CaO) center dot 7(Al2O3) inclusion will form in the molten steel. Calculated results show that with calcium treatment of liquid steel the stable CaS forms easily and the aluminum deoxidizing product Al2O3 is easily modified to low-melting calcium aluminate 12(CaO) center dot 7(Al2O3). In order to completely modify the Al2O3 to low-melting calcium aluminate (CaO) center dot (Al2O3) and 12(CaO) center dot 7(Al2O3), the calcium treatment of liquid steel should carry out in conditions of low [S] and >= 1600 C-omicron, and the sulfur wire feeding operation after soft argon stirring in refining process, it is available to obviously decrease the occurrence of nozzle blocking.