Effects Of Rare-earth Yttrum On Inclusions And Microstructure Properties Of GCr15 Bearing Steel

Bearing is an indispensable steel joint of mechanical transmission.Bearing steel is recognized as the king of steel.The cleanliness and uniformity of bearing steel are the main factors affecting the longevity of bearing.In this paper,GCr15 bearing steel was taken as the research object.Through thermodynamic calculation analysis and laboratory experiments,the influences of rare earth Y on the inclusions and microstructure and properties of steel were studied.At the same time,the heat treatment process of rare earth Y microalloying treatment of GCr15 steel was discussed.The main research results are made as follows:1.Through thermodynamic calculation analysis and SEM energy spectrum analysis,the inclusions in the test steel without rare earth are mainly Al₂O₃inclusions,Mn S inclusions and Mn S-Al₂O₃composite inclusions precipitated with Al₂O₃as the core.Al₂O₃inclusions are generated in the molten steel,and Mn S inclusions are generated in the solidification process.The main inclusions in GCr15 steel treated by Y microalloying are yttrium oxide,yttrium oxide sulfide,yttrium sulfide and a small amount of rare earth composite inclusions.When the rare earth content in steel is low,there will be Mn S-RE₂O₂S wrapped composite inclusions with rare earth oxygen sulfide as the core.Y₂O₃,Y₂O₂S and YS inclusions can be precipitated in molten steel,while Y₂S₃inclusions cannot be precipitated in molten steel.The Al₂O₃inclusions in test steel are transformed into rare earth oxides and rare earth oxygen sulfides after rare earth modification.The inclusions in rare earth test steel are mostly spherical rare earth inclusions with small size and regular shape.2.By adding rare earth Y,the pearlite lamellar spacing of GCr15 bearing steel decreases after as-cast and forging.After quenching,the austenite grain size decreases from 17.16μm to12.09μm,and the grain size increases from 8.44 to 9.34.After the rare earth GCr15 bearing steel was treated by different tempering processes,the carbide size and area fraction were positively correlated with tempering time and tempering temperature.The addition of rare earth Y can improve the size and morphology of the second phase carbides,promote the spheroidization process of carbides,and make them finer and dispersed.3.By adding rare earth Y,the hardness of GCr15 bearing steel in as-cast,forging and annealing state has been significantly improved,as-cast hardness increased by 14.15%,forging hardness increased by 13.69%,annealing hardness increased by 3.4%.The test results of hardness and impact properties of GCr15 bearing steel under different tempering processes show that the overall performance of GCr15 bearing steel is the best when the content of rare earth Y is 86 ppm,the tempering temperature is 170℃and the holding time is 3 h.