Effect Of Deoxidization Of Magnesium And Aluminum On The Cleanliness And Microstructure Of GCr15 Bearing Steel

GCr15 bearing steel is one of the most typical representative high carbon bearing steel.Although there was little change in the composition of GCrl5 bearing steel since it came into being,its fatigue life has increased several times compared with earlier years because of the increasing of its cleanliness.Oxide inclusions greatly affect the fatigue life of bearing steel,for which oxygen content is a major index to measure the quality of bearing steel.Thus,the key to produce high-quality bearing steel is to reduce oxygen content and to control the inclusions.In order to obtain better effect of deoxidation,which could improve the quality of bearing steel,this paper tried to study on new deoxidizer.Magnesium is an extremely active metal with a strong affinity for oxygen,and the thermodynamic results indicated that the effect of magnesium deoxidation is excellent.This paper decided to empolder AI-Mg complex deoxidizer.Factsage was used to calculate the effect and law of inclusions precipitation when the mass fractions of magnesium and aluminum changed.The result showed that the effect to inclusions precipitation was primarily depended upon magnesium,and the mass fraction of magnesium improving caused MgO·Al2O3 precipitation and obvious effect on the precipitation of sulfide.MoSi2 electric resistance furnace was used in this study.Metal powder was used to prepare deoxidizer with different mass fractions of magnesium.In experiments,deoxidizers were added to GCr15 bearing steel,and detected the mass fraction of oxygen in ingots.The results showed that the oxygen content can be decreased to the lower level by magnesium-aluminum deoxidizer,for example,the mass fraction of oxygen was 80×10-6 in the ingot without deoxidizer while it was 7.3×10-6 with 2.0 g 7-2-1 deoxidizer.A large amount of MgO·Al2O3 and compound inclusions which were in the size of 2?3 pm precipitated,thus the percentages of small size inclusions increased and total areas and average diameters of inclusions decreased.Adding deoxidizer refined the as-cast microstructure,decreased second dendrite arm spacing and reduced the degree of segregation,at the same time,carbides were refined and the reticular structure of carbides was broken.