Slag System Optimization And Quality Stability Control Of Bearing Steels

As the main material of bearing,the quality of bearing steel directly affects the stability and reliability of bearing.The key factors affecting the quality of bearing steel are the total oxygen content and inclusion level in the steel.At present,the total oxygen content control of international advanced bearing steel manufacturers has reached below 5×10^-4%,but the total oxygen content control of bearing steel in some domestic steel plants is lower than the international advanced level.Therefore,how to reduce the total oxygen content and inclusion level of bearing steel,achieve stab control of the quality of bearing steel,and enhance product competitiveness is an urgent problem for domestic bearing steel manufacturers.In order to improve the metallurgical quality of bearing steel in a steel plant and reduce the content of total oxygen and the level of inclusions in the steel,the production process of bearing steel in a domestic steel plant was systematically sampled and analyzed.The results show that the oxygen content of bearing steel fluctuates obviously,ranging from 4.2×10^-4%to 10.8×10^-4%,and the oxygen content difference between adjacent heats can reach 3.8×10^-4%;The nitrogen increase rate of LF is 119.67%,and the nitrogen removal rate of VD is only 29.25%;The inclusion floats for a long time.Therefore,in this study,the above problems are studied from two aspects:The influence of the alkalinity（R）of refining slag and Ca O/Al₂O₃（C/A）on inclusion removal is studied by using the Fact Sage 7.1 thermodynamic calculation software and combining with experiments,and the optimization scheme of refining slag system is proposed;The VD argon blowing process is optimized by using Fluent fluid simulation software.The influence of the number of blowing holes,installation position,included angle and argon blowing flow rate on the ladle flow field is studied,and the optimization scheme is proposed.Industrial tests are carried out according to the optimization results.The research conclusions are as follows:（1）When the alkalinity is constant,with the increase of C/A,the total amount of inclusions in molten steel shows an upward trend,and large inclusions increase,accounting for 27.74%;When C/A is constant,with the increase of alkalinity,the total amount of inclusions decreases and the proportion of large inclusions increases;The inclusion area decreases with the increase of R;The inclusion area increases with the increase of C/A;When R=5,C/A=1.5,the inclusion removal efficiency is the highest,26.67%;Therefore,the refining slag with R=5～6 and C/A=1.5 can obtain good inclusion removal rate and proper inclusion size distribution.（2）Double air inlets are used.The installation position of the air inlet is 0.5 R,and the included angle is 150°.The flow field of molten steel with argon blowing flow rate of 60～70 NL/min is evenly distributed,the proportion of"dead zone"is small,the mixing effect is good,the slag volume at the slag metal interface is small,and the mixing time is small.（3）The industrial test results showed that the average oxygen content decreased by 9.7%compared with that before optimization;VD denitrification efficiency increased by 30.43%;The soft blowing time decreased by 22.36%;The maximum inclusion size decreases by 22.15%.