Utilization Of Rare Earth Niobium And Titanium Resources Of BT700L Automobile Beam Steel Baiyun Obo

The Bayan Obo mine is rich in niobium resources.Decades of research have improved the taste and recovery rate of the niobium concentrate.However,due to the poor,fine,and impurity characteristics of the Bayan Obo mine,it is difficult to efficiently enrich it,and the smelted ferro-niobium contains inclusions a lot of other impurities are difficult to use.The researchers used the tunnel kiln-tank gas-solid selective reduction method to simultaneously extract the niobium and titanium in the ore to obtain the rare earth niobium-titanium composite alloy,which improved the grade and recovery rate of the niobium-titanium alloy and reduced the impurities in the alloy.The FactSage thermodynamic software is used to calculate the changing trend and law of the content of niobium and titanium during the alloying of the rare earth niobium-titanium composite alloy by the refined slag.Considering the alkalinity,melting point and viscosity of the refining slag,select suitable refining slag for laboratory smelting.A 25Kg vacuum induction furnace is used to smelt BT7000L automobile beam steel with or without refining slag.The alloys added are rare earth niobium-titanium composite alloy+ferro-titanium and ferro-titanium+ferro-niobium.Use direct reading spectrometer and C?S analyzer to detect the composition of steel,use X-ray diffractometer to detect the composition of refining slag,and get the law of the influence of refining slag on the alloying of niobium and titanium.A Zeiss microscope was used to observe the structure and grain size of the steel,and a field emission scanning electron microscope was used to observe the steel inclusions and precipitates.Compare the differences in the structure,inclusions,and precipitates of the as-cast experimental steels in the two smelting methods.And to study the changes in the structure and precipitates of the experimental steel smelted with rare earth niobium-titanium composite alloys after rolling.The thermodynamic calculation results show that after adding the refining slag in the LF refining stage,the niobium content has no effect,the titanium content in the steel is greatly reduced,the yield is less than 10%,and the silicon content is greatly increased,and the excess is 50%of the total added amount.By calculating the melting point and viscosity of refining slag with different alkalinity and the change of alkalinity and temperature,it can be known that 55%Ca O?25%Al₂O₃?15%Si O₂?5%Mg O refining slag is more suitable for subsequent laboratory smelting.The laboratory smelting verified the rule that the addition of refining slag reduces the titanium content.When ferro-niobium+ferro-titanium are added to the refining slag,titanium is reduced by 0.074%and silicon is increased by 0.042%;when the rare earth niobium-titanium composite alloy+ferro-titanium is added to the refining slag,titanium is reduced by 0.0785%and silicon is increased by 0.0458%.When the refining slag is added after alloying,the Ti in the steel reacts with the Si O₂in the refining slag to form Si and Ti O₂,and the generated Ti O₂ reacts with the Ca O in the refining slag to form refractory Ca Ti O₃and stay in the slag.The structure of the as-cast experimental steel is composed of ferrite and a small amount of bainite.The addition of rare earth niobium-titanium composite alloy does not change the structure type,but changes the number and size of inclusions in the steel.The niobium-titanium precipitates in steel are mostly Ti C,and their size is about 100nm.A few are(Ti,Nb)(C,N),with a size between 1 and 4?m,and most of them are square in shape.The precipitates in steel smelted with rare earth niobium-titanium composite alloys are more dispersed and smaller in size.The structure is refined after rolling,and the structure of the experimental steel is composed of ferrite and a small amount of bainite.