Research On The Behavior Of Non-Metallic Inclusions Of Bearing Steel In The Refining Process

Basing on the bearing steel refining process of EAF-LF-VD-CC and the current condition of Nanjing Iron & Steel Union CO.,LTD electrode furnace factory, this subject researches on the transmition rules about nonmetallic inclusions' amount, size, type and distribution comprehensively by the way of systeme sampling and compositive analysis. Mean while the infl uence of oxygen content in bearing steel is also analisysed. Results show that:(1) The number of inclusions in the steel treated by VD are less than that treated by LF, the number of inclusions in the rolled product reduces sharply than that in the VD procedure. The number of the inclusions in LF procedure is 3.5/mm², which in VD procedure is 3.0/ mm², while in the rolled product is 1.4/mm².(2) Inclusions in the steel after LF procedure are mainly Al₂O₃, aluminosilicate, sulfide, ametabolic punctuate inclusions and chromium ferrate. After VD procedure there are no chromium ferrate but mainly Al₂O₃, aluminosilicate, sulfide and ametabolic punctuate inclusions. In the rolled product, kinds of inclutions reduce more, there are only aluminosilicate and sulfide.(3) Rating results of 100 furnaces steel show that A, B-type inclusions are in line with international requirements, D-type inclusions of fine lines have failed furnaces, which accounts for 1%. The average of the 3 Class inclusions are in line with international requirements.(4) The deoxidation system of refining furnace should be strdngthened, control the aluminum content in liquid steel at about 0.025%; The content of sulfur shoud be reduced to no more than 0.0009% to reduce the sulfide inclusion.(5) Thermodynamic calculations show that 1823K, [Si] relates to 0.21%, when only aluminum participates GCr15 deoxidization, ifα[Al] >0.000375%, it willprecipitate A1₂O₃; ifα[Al] <0.000166%, it will precipitate SiO2; ifα[Al] ranges between them it will precipitate A₃S₂.When calcium exists in the steel,α[Al] =0.01%, ifα[Ca] >10^-1.4 it will generate C₁₂A₇; if 10^-1.4<α[Ca] <10^-1.4 it will generate CA₆; if 10^-7.9<α[Ca]<10^-4.9 it will generate CA₂, and ifα[Ca] <10⁽-7.9 it will generate CA.(6) The experimental results show that when R> 5, CaO/Al2O3 is between 1.7 to 1.8, namely the Al₂O₃ is about 30% of the slag, it is favorable of controlling the oxygen content and inclusions in molten steel.