Experimental Study On The Deoxidization Of Steel By Using Methane And Its Influence On Inclusions

With the level of industrialization improving,the market has put forward higher requirements on the comprehensive performance of steel products,especially the hash requirements about the quantity and morphology of inclusions in the special steel.Conventional deoxidization method depends on the requirements in steel and chooses the appropriate deoxidizer into steel so that the oxygen content of steel gets to the normal range,which is fast,however,whether deoxidization products are solid or liquid will inevitably remain in the steel,which causes secondary pollution.Therefore,it is quite significant to choose which one of deoxidizers to reduce the oxygen content and reduce the content of inclusions in steel to improve the steel purity.Based on this consideration,this paper utilizes a theory that it uses the methane as a deoxidizer to put into the molten steel and produce CO and H₂ O at the high temperature with the oxygen in the steel,to reduce the oxygen content in steel.In addition,it is very important to optimize the traditional deoxidization process and improve the purity of molten steel,for which deoxidization products in gaseous form are difficult to remain in the steel.This paper,using methane to process deoxidization of liquid steel,studies that the flow and the ventilation time of methane（mixture of methane and argon）affect the contents of steel liquid oxygen,carbon and hydrogen,and studies changes of the inclusions in the steel using different deoxidizers to deoxidize at the same time.The main conclusions are as follows:（1）When the methane is put into the oxygenation experiment,the oxygen content in steel is reduced rapidly and terminal point of oxygen content can be reduced to about 40 ppm,as well as extending aeration time and increasing the gas flow are beneficial to remove the content of oxygen effectively.When the methane flow rate is the same,a mixture of methane and argon gas is clearer and faster to reduce oxygen content and the utilization rate of methane is higher.16-minute pure liquid argon blown into the molten steel,the liquid oxygen content of steel decreases by 75.1ppm,whose result shows that the argon gas can reduce the liquid oxygen content of steel,however,the deoxidization effect is limited.（2）From the point of the whole process of deoxidization,the oxygen content in liquid steel decreases quickly,and the average gas deoxidization rate is faster.The utilization rate of methane and gas deoxidization rate are higher than 8 minutes before the ventilation.After 8 minutes,the oxygen content in steel decreases steadily and the average deoxidization rate and utilization rate also decrease gradually.Therefore,to reduce the cost of production and improve the utilization rate of methane,the gas can be injected into a larger flow in the early stage,and in the later stage the gas flow rate can be reduced properly or other deoxidizers can be used to deoxidize.（3）With the aeration time increasing,content of carbon and hydrogen in steel increases gradually by putting methane into the liquid steel.Compared with pure methane,using mixed gas can slow down the increasing speed of hydrogen content in steel.When the methane flow rate is the same,whether using argon or not has little effect on the carbon content in the steel,but the carbon and hydrogen content in the steel is significantly increased compared with before the deoxidization.So the practical production of deoxidization with methane should use VD refining furnace of molten steel to reduce the hydrogen content in steel.In addition,carbon,which is produced due to the high temperature decomposition of methane,can make carbon of steel liquid increase rapidly.So the methane is more suitable for the use of ball bearing steels,tool steel and other high carbon steel productions.（4）Compared with Al,the quantity and type of inclusions in the steel are obviously reduced after using methane to deoxidize,but to some extent the size of inclusions decreases.Besides,the content of Al2O3 inclusions in steel is obviously reduced and at the same time,after using methane to deoxidize,the deoxidization products are mostly regular circles.Compared with the pure methane,mixed gas of methane and argon has little effect on the size of inclusions;however,compared with Al,the content of Al2O3 inclusions is dramatically reduced,and the mixed gas can decrease the number and type of inclusions in steel.