Traditional spring steel 50CrVA was taken as the research object,and the bainite transformation was realized by austempering at 350,400,450 ℃ in the furnace after water mist+air fast cooling.The effect of austempering temperature on microstructure and properties of the 50CrVA steel was studied by means of thermal simulation,SEM,XRD,tensile and impact tests.The results show that the bainite transformation rate first increases and then decreases with the increase of austempering temperature,and the transformation rate is the fastest at 400℃.The bainite transformation quantities at 350 ℃ and 400 ℃ are the same and higher than that at 450℃,this is due to the precipitation of carbides,which reduces the carbon content in the undercooled austenite,the bainite transformation is completed,thus obtaining full bainite microstructure.With the increase of austempering temperature,the bainite,cementite and M/A structure become coarser,resulting in a significant reduction in tensile and impact properties,and the fracture mode gradually changes from quasi-cleavage fracture to cleavage fracture.
50CrVA spring steelbainiteaustempering temperaturemicrostructure evolutionmechanical properties
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