Control technology for oxygen content and inclusions of gear steel

The control of oxygen content and composition and the transformation conditions of non-metallic in gear steel are calculated with the thermodynamic calculation software Factsage.The results show that the composition of non-metallic with high plasticity in 20CrMoH steel is as follows(mass fraction): SiO2 0% to 10%,Al2O3 22% to 55%,CaO 42% to 60%,and MgO 5% to 10%.Under this condition,the mass fraction of aluminum in molten steel is above 0.020%,that of calcium is above 0.7×10-6,and the activity of oxygen in molten steel is about 0.000 5%.If the compositions of refining slag with CaO40%,Al2O3≤37%,MgO 10%,(%CaO+%MgO)/%SiO2=10,and the SiO2 content as low as possible are selected,Al2O3 and MgO·Al2O3 in molten steel can transform into calcium aluminates with low melting point.It is found that the contents of T[O] at the end of LF and RH refining both decrease with the increase in slag basicity,and the content of T[O] decreases with increasing the content of Al2O3 in the slag.In the refining process,the composition of the non-metallic changes in order of inclusions of the Al2O3 system→inclusions of the MgO-Al2O3 system→inclusions of the CaO-MgO-Al2O3 system,among which the change of of the MgO-Al2O3 system to of the CaO-MgO-Al2O3 system is inwardly from the outside surface and the reaction speed is relatively slower.Thus,at the end of the ladle furnace refining(LF),there are still many unchanged MgO-Al2O3 system inclusions.The T[O] content of the steel significantly affects the composition change of the and decreasing T[O] content favors the change of inclusions.