Effect Of Microelements On Microstructure And Property Of Cast Steel

Cast steel is one of the most commonly used materials in construction, which has higher melting point,more broad range of crystallization temperature,bad fluidity and coarse cast grains. Most of grain refinement methods are unsuitable for cast steel, because it is normally formed through cast.Microelements which are mostly used in thermo-mechanical controlled processing play a important role in the development of steels.The microalloyed steel developed in recent years, which is employed in various industrial sectors. It was reported that microalloy elements Ti, V, Nb, etc and rare earth (RE) additions can play a excellent function in refinement microstructure of steel ingot. The studies and applications about effects of RE and microalloy elements on cast steel are few, and the action mechanism is not well understand.Oxides metallurgy is defined as a new technology for refining grain by use dispersion of fine nonmetallic inclusions as intragranular ferrite nucleated sites.In the inwestigated oxides of Ti,Al,Zr, Ti oxide could promote the formation of acicular ferrite, which can refine microstructure and improve the toughness and strength. Presently, Oxides metallurgy is mainly applied in improvement of the toughness in the welding expansion zone of the low-medium carbon steel plate and the toughness of hot forged steel.There is few research in the common carbon steel and on process conditions of intragranular ferrite formation.In this study, silicon and manganese, titanium and aluminium were used in preliminary and final deoxidation processing,respectively.The morphology,chemical composition,size and type of nonmetallic inclusions were controlled by these additional elements. And we get the inclusions that can promote the formation of acicular ferrite. Through employing different hot processing, we investigate the effect of different content of Ti and Al on cast steel microstrucure. Meantime,the effect of nonmetallic inclusions on Intragranular Acilcualr Ferrite was also investigated..The results showed that the type of inclusions have changed largely. The produced inclusions are mainly Ti oxides and Ti nitrides,Al oxides,Ti,Al composite oxides and sulfides. These inclusions are fine and the size is mostly less than 3 u m. Except of quadrilateral TiN, other inclusions are mostly spherical shape. To get appropriate inclusions,the optimum component of titanium is about 0.05%-0.07%,aluminium is about 0.01%.Because of the addition of titanium and aluminium, the cast microstructure of steel is improved obviously and it is propitious to promote the formation of Intragranular Polygonal Ferrite,which having the effect of refining grains.Austenitizing temperature, time at maximum.Temperature and cooling rate play crucial roles in promoting the formation of Intragranular Acilcualr Ferrite.And the proper hot processing for the formation of large numbers of Intragranular Acilcualr Ferrite is that austenitizing temperature is 900℃, time at maximum temperature is 10min and the cooling rate chooses normalizing.The content titanium and aluminium has a important effect in the formation of Intragranular Acilcualr Ferrite. Without the addition of titanium and aluminium, there is no Intragranular Acilcualr Ferrite not only in cast microstructure,but also in hot processing microstructure.It is showed that with the increase of the content titanium and aluminium, the numbers of Intragranular Acilcualr Ferrite is decreasing.And the optimum component of titanium is about 0.05%-0.07%,aluminium is about 0.01%.The results ofinvestigated by SEM and EDS showed that Ti,Al,O,S,Mn composite inclusion and Ti2O3 both could promote the formation of Intragranular Acilcualr Ferrite excellently. And the size of inclusion promoting the formation of Intragranular Acilcualr Ferrite is less than 3 u m.The results showed that the content of titanium and aluminium affect the mechanical property of cast steel largely.The hardness has a increase thrend with the content of titanium and aluminium increasing.Conversely,strength.and ductility have a decrease thrend.Intragranular Acilcualr Ferrite could remarkably improve the elongation and area reduction,and the ductility is also enhanced.