Inclusion evolution in refining and mould casting process of AISI431 stainless steel
To study the evolution of inclusions in AISI 431 stainless steel during refining and mold casting,control the inclusions reasonably,and improve the qualified rate of AISI 431 flaw detection,the evolution of inclusions in AISI 431 stainless steel produced in"EAF+AOD+LF+RH+MC"process was analyzed by using OTSInca and thermodynamic software FactSage 8.0.The results show that the removal of inclusions by RH vacuum treat-ment can greatly reduce T[Al]and Als in steel.The quantitative statistical results of inclusions show that A12O3 is the main component of inclusions in steel,and it increases to approximately 90％in final steel;After RH vacuum treatment,the average diameter of inclusions in steel reaches the maximum due to the collision polymerization of cal-cium aluminate inclusions,and these inclusions are largely removed by soft blowing after RH vacuum treatment,and the inclusions in the final steel are greatly reduced;At the same time,the number of inclusions per unit area reached the minimum of 25/mm2 after RH vacuum treatment,and the number of inclusions in the final steel increased slightly due to secondary oxidation.The typical morphology of inclusions in the steel was observed by scanning electron microscope.It was found that in the pre-LF steel,there were mainly large-sized Al-Ca-Mg-Si-O inclusions,mainly Al-Ca-Mg-Si-O inclusions and some MgO inclusions,and calcium aluminate inclusions formed by Al seizing O from calcium silicate inherited by AOD;After RH vacuum treatment,the inclusions in the steel are mainly small-sized composite inclusions composed of Al-Ca-Mg-Si-O partial MgO,Al2O3 and calcium aluminate.The MgO·Al2O3 inclusions in the steel are decomposed by vacuum and decreased from 21.95％before RH vacuum treatment to 7.46％.The results of FactSage thermodynamic calculation show that the main inclusions in the steel after LF and RH refining are CaO·2MgO·8Al2O3,CaO·Al2O3 and Spinel;Compared with LF refining,the mass proportion of Spinel phase and inclusions in steel decreased after RH vacuum treatment.Compared with the traditional process,the qualified rate of flaw detection increased from 72.5％to 98.6％,non-metallic inclusion K5(Inclusion Evalua-tion Standard DIN50602)is 0,and the cleanliness and qualified rate of AISI 431 stainless steel were well controlled.
AISI 431 stainless steelLFRHinclusionqualified rate of flaw detection
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