Study on Thermodynamics of Inclusion Formation in GCr15 Bearing Steel
In order to grasp the formation mechanism of bearing steel inclusions in a large steel enterprise in China,the starting precipitation temperature of GCr15 bearing steel inclusions is calculated by thermodynamics and analyzed accordingly.The results show that the precipitation temperatures of oxide and CaS inclusions in steel are much higher than the liquidus(1 727.85 K),and can be precipitated in liquid steel,while the MnS and nitride inclusions can only be precipitated during the solidification and cooling of the billet.At the solidification front of the casting billet,the segregation degree of Mn and S increases with the increase of the solid phase ratio,and the segregation of S is more serious than that of Mn.When the solid phase ratio at the solidification front reaches 99.1％,MnS inclusion will be precipitate,and w(Mn)and w(S)in the molten steel are 1.043％and 0.565％.Similarly,the segregation degree of five elements(N,Ti,Nb,Al and V)increases with the increase of solid phase ratio,and the largest segregation degree is N,followed by Ti,Nb,Al and V.During the cooling and solidification process,the element N in the molten steel preferentially combines with Ti,which reduces and restrains the precipitation of fine AlN,NbN and VN inclusions.
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