Mechanism Study On Improvement Of Inclusions And Liquation Carbide In GCr15 Bearing Steels By RE-Mg Treatment

With the rapid development of Chinese Iron & Steel Industry,Chinese yearly steel production has already ranked first in the world,but the quality of top steel products still has a certain gap with foreign developed countries.For some bearings and other components also rely heavily on foreign imports which use in high-speed railway,wind power,precision machine tools,shields machines and other heavy equipment.The cleanliness,control of carbide and consistency of product quality is the main difference between the product quality of bearing steel in China and foreign products.Therefore,it's most important to the quality of bearing steels that further improve the cleanliness,control of carbide.Existing research has initially found that magnesium and rare earth treatment have a good effect on the cleanliness and control of carbide in steels,but its action mechanism,especially in the action mechanism of carbides in steels is still widely discussed.Therefore,it is of great significance to study the action mechanism of magnesium and rare earth on inclusions and carbides in steels to apply this technology to actual production better and improve the product quality of bearing steels.In this paper,the magnesium and rare earth-magnesium added in the GCr15 bearing steel to study the action mechanism of magnesium and rare earth on inclusions and carbides in steels.The following conclusions were obtained under experimental conditions:Magnesium and rare earth-magnesium treatments have an improved effect on inclusions in GCr15 bearing steels.The higher magnesium content in steels,the proportion of small inclusions in 3.559-5?m is higher,the proportion of lager inclusions in is lower.Rareearth-magnesium treatment can further improve the proportion of small inclusions on the basis of magnesium treatment,and large inclusionsscale out 10?malmost disappear.(1)The effect of magnesium treatment on the carbides in GCr15 bearing steels has been first improved and then deteriorated.And there is an optimal range to reducethe number and minimize the size of carbide in the steels.In this experiment,when the magnesium content was 16 ppm,the effect of improving the carbide in the steel was the best.When the content of magnesium continues to increase,the amount of carbide increases,even exceeds untreated steel,but the average size of carbide is always better than untreated steel.(2)In the GCr15 bearing steels with rare earth-magnesium composite treatment,the addition of rare earth has an adverse effect on the carbides when the content of magnesium is low,which increases the amount and average size of carbides in steels.And when the content of magnesium is high,the addition of rare earth can further improve the carbides in steels,the amount and average size of carbide in steels can be reduced.However,compared with the magnesium treated steel,the amount and average size of carbides in the rare earth-magnesium composite treated has been increased.(3)Magnesium and rare earth elements segregate at grain boundaries,and the diffusion of elements at the grain boundaries is easier than intergranular diffusion.Therefore,the segregation of magnesium and rare earth in the grain boundary hinders the accumulation of the elements around the carbides,which may be the reason for inhibiting carbide growth.After SEM-EDS observation,show that carbide tends to adhere to MnS inclusions and grow up.The influence of magnesium and rare earth on the MnS and MnS-MgS inclusions in steels may be the reason for the change in the amount of carbides.