Study On Solidification Precipitation Behavior And Control Mechanism Of Inclusions In Twin Induced Plastic Steel

The inclusion behavior of Fe-Mn-C-Al TWIP steel and the influence of inclusions on solidification structure were studied systematically.The inclusions in Fe-Mn-C-Al twin-induced plastic steel were observed and analyzed by metallographic microscope,scanning electron microscope and energy spectrometer.The results show that the following eight inclusions are mainly present in Fe-Mn-C-Al TWIP steel:Mn S?Mn O?Al N?Al₂O₃?Al?O?N,Mn S-Al N,Mn S-Al₂O₃,Mn S-Al?O?N.The thermodynamic precipitation of typical inclusions is calculated by thermodynamics,and it is concluded that Al N and Al₂O₃ inclusions in the composite inclusions Mn S-Al N?Mn S-Al₂O₃ are precipitated first as heterogeneous nucleation rate,then Mn S inclusions are then attached to their surface,and finally the composite inclusions are formed.By adding niobium element,the change rule of inclusions in TWIP Steel of Fe-Mn-C-Al system was studied.In addition to the inclusions mentioned above,new inclusions,Nb C and mns-aln-nbc,were produced in the matrix of the Fe-Mn-C-Al system TWIP Steel after adding niobium.The analysis shows that the number of Al N and Al₂O₃ inclusions in the TWIP Steel is significantly reduced after adding niobium,and the size of Nb C inclusions is small,generally between 1 and 3?m.The thermodynamic precipitation temperature of Nb C inclusions is also rising with the increase of Nb content,and the size of various inclusions is obviously reduced with the addition of Nb.After niobium was added to TWIP Steel,a certain amount of Nb C inclusions appeared in the steel,and its solidification structure also changed obviously.The crystallographic analysis of Nb C produced in TWIP Steel by two-dimensional lattice mismatch shows that?100?of Nb C inclusions and?100?of austenite are the most easily precipitated,compared with other inclusions,Nb C inclusions are more easily precipitated as heterogeneous nucleation.The statistical analysis shows that the size of equiaxed crystal and columnar crystal in the solidified structure of TWIP Steel after Nb C precipitation is obviously reduced,and the decreasing proportion is about66.32%,which improves the quality of solidified structure.