Evolution mechanism and key control processes of inclusions in high carbon chromium bearing steel during whole process
To study the evolution of inclusions in GCr15 bearing steel,the Aztec-Feature inclusion automatic soft-ware configured with Zeiss Ultra55 scanning electron microscope was used to statistically analyze samples in EAF-LF-RH-CC each process with over 200 mm2 scanning area.The evolution of inclusion morphology,composition,quantity,size and distribution,etc.in each process was analyzed.The result indicates that,the main inclusions in GCrl5 bearing steel are mainly Al2O3 in EAF exit.In the LF refining process,the main inclusions are MgO-Al2O3 and Al2O3-MgO-CaO with a little CaO.After RH start,the content of CaO in the inclusions increases,forming Al2O3-CaO-MgO inclusions.Finally,the average composition of inclusions in the tundish is 56A12O3-22CaO-7MgO-8CaS.At the same time,the LF-RH refining stage and the early stage of RH soft blowing have significant removal effect on inclusions in steel,with removal rate of 95.6%.However,with the increase of RH soft blowing time,it has little effect on the removal of T[O]and[N]in the steel,and even large inclusions may be involved,leading to T[O]and average size of inclusions increase.According to the calculation of FactSage equilibrium thermodynamics,when w(T[O])=7 × 10-6,w([Mg])≥0.4 ×10-6 and w([Ca])≥0.16 × 10-6 in GCr15 bearing steel liquid,mag-nesium aluminum spinel and solid calcium aluminate inclusions can be generated respectively.The research results provide theoretical guidance and reference to the production of bearing steel.