Research On The Refining Process Of Bearing Steel

High carbon bearing steel with 1.0% C, 1.5% Cr is an important special steel grade, which represent technology level of high quality clean steel. Oxygen content in bearing steel is a major index to judge its quality because oxide inclusion greatly affect the fatigue of bearing steel. Therefor one of the bottlenck problems to produce high-quality bearing steel is how to reduce oxygen content and get ride of the harmful inclusion.This subject is based on the bearing steel process of EAF-LF-VD-CC and the current condition of Nanjing steel and union limited company electric strove factory, and on-site sampling. Then The pattern and competent of typical inclusions were analysed by scanning electron miroscope and dispersive spectrocope. The inclusions formed thermodymatic was couned, which provide a favorable basis for removel of inclusions and improving liquied steel. At the same time. The factors of deoxidization and the formation reason of inclusions were analysised, though researching of deoxidization system, slagging system(including the choice slag, slagging volume controle),blowing argon mixing system, VD vacuum, temperature control. The result show that:(1)High basicity refining slag is good for desulfurizing and deoxidization, sulfur capacity Ls increase and oxygen content reduce with the optical alkalinity rasing. [Al], [Si], [C] in molten steel can reduce CaO in slag, which can spontaneous combine with [Al], [0] forming pherical inclusion. The experimental show that class D inclusion is higher, which can rearch 0.5 to 1.0.(2)The performance of bearing steel decrease gradually with nitrogen, titanium content increase. The existence state of nitrogen and titanium in molten steel is solution, but the TiN inclusion which is damaged to the steel performance is formed in two phase area of solide and lique and the size of inclusion is larger, when nitrogen and titanium is higher. If titanium content less than 30ppm and nitrogen is less than 60ppm, the inclusion precipitated below temperature solidus has little effect on the property owing to refining.(3) The carbon content of the furnace need to strictly control in order to guarantee the content of carbon more than 0.15%, when EAF tap off. The sample have bulky grain chromite inclusion from inclusion decetion result. Accoding to thermodynamics know that bulky grain chromite inclusion can be generated, when the content of oxygen is reach about 100ppm. So the pre-deoxidation process should be strengthened.(4)The refining furnace deoxidation work must be strengthened in order to control final Als content and the margin, the margin should less than 0.003%, and final Als content should be controlled about 0.025%.(5) Limite vacuum must be less than 67pa,and kept more than 15 minutes. Soft blowing argon should be more than 20 minutes after vacuum treatment.