GCr15轴承钢夹杂物形成机理研究

Study on Thermodynamics of Inclusion Formation in GCr15 Bearing Steel

为了掌握国内某大型钢企轴承钢夹杂物形成机理,通过热力学计算对GCr15轴承钢夹杂物开始析出温度进行了相应的分析研究。研究结果表明:钢中氧化物、Ca S夹杂的析出温度均远高于液相线1 727.85 K,可以在钢液中析出,而Mn S、氮化物夹杂只能在铸坯凝固冷却过程中析出。在铸坯凝固前沿,元素Mn、S的偏析度随着固相率的增大而增加,S比Mn偏析的更为严重,当凝固前沿固相率达到99.1%时,便会析出Mn S夹杂。此时,钢液中的w(Mn)为1.043%,w(S)为0.565%。同理,N、Ti、Nb、Al和V元素的偏析度随着固相率的增大而增加,偏析度最大的是N元素,其次为Ti、Nb、Al和V元素。在铸坯冷却凝固过程中,钢液中N元素优先与Ti结合,减少并抑制了细小AlN、Nb N和VN夹杂的析出。

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 Ca S 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 Al N,NbN and VN inclusions.