High purity, small size of inclusions is widely used in high-quality production of automotive 20CrMoH gear, generally accepted control objectives, including steel: w (T [O]) control in 15 10-6 or less, with a narrow hardenability ( ?4HRC), to improve the fatigue strength of the anisotropy and enhance the cutting performance and so on. After years of exploration, including the refining slag system chosen, calcium treatment, including complete sets of metallurgical technology has matured to ensure production of high quality steel gears. Panzhihua Iron and Steel use of "large-scale converter 2, continuous casting" process volume, the advantages of stable quality, high-quality gear carried out tests of steel production, and achieved good results. Panzhihua Iron and Steel smelting process in large-scale conditions, adding about 12kg per ton of steel refining slag of high basicity and about 1kg of aluminum particles, can make good white slag, steel slag composition of the desired goals; steel oxygen activity of 3 10 -6 or so, and sulfur content in steel <0.005%, calcium treatment will be Ca / Al control in 0.08, modified to meet the requirements of inclusion, and to higher steel content in the Als still has good casting properties; Experimental heats the slab T [O] of the mass fraction (12 ~ 26) 10-6, except the first furnace, tundish, and the remaining 6 furnace T [O] the mass fraction of less than 15 10-6. Inclusion in the slab are mainly CaO-MgO-Al2O3-CaS system, the other group element content of small, mostly spherical inclusions, most of the size of less than 5 m, and the formation of the outer surface of mCaO nAl2O3 surrounded by a layer of CaS; precision control components test good gear steel, the hardenability bar to meet standard requirements, J9 and J15 are controlled by the bandwidth at the HRC value in less than 4.