Experimental Study On Preparation Of 42CrMo Steel By Direct Alloying Of Molybdenum Oxide

Molybdenum is a frequently used alloying element that greatly enhances steels strength,hardness,wear resistance,and corrosion resistance.Typically,the ferromolybdenum alloying process is utilized in the smelting of molybdenum-containing steel.Unfortunately,this process generates significant amounts of harmful byproducts such as CO₂,SO₂,NO_x,and soot,resulting in high energy consumption and pollution.Molybdenum oxide direct alloying technology is to add molybdenum oxide directly into molten steel,and reduce molybdenum oxide to[Mo]element into molten steel through reduction reaction with carbon,silicon,manganese,iron and other elements in molten steel to achieve the purpose of alloying steelmaking.In this paper,taking 42CrMo steel as the research object,the reaction mechanism of the direct alloying of molybdenum oxide is studied through thermodynamics and kinetics.The best way to add 42CrMo steel and the reasonable method for molten steel to suppress the volatilization of molybdenum oxide;the microstructure and inclusion morphology of 42CrMo steel smelted by direct molybdenum oxide alloying and molybdenum-iron alloying were analyzed by metallographic and SEM methods and components,the following conclusions are obtained:（1）Based on the Gibbs free energy change of the reaction between molybdenum oxide and various reducing agents in the standard state,the reduction of MoO₃ by elements such as[C],[Si],[Mn],and Fe in the molten metal was calculated in the steelmaking state.The reaction Gibbs free energy and selective reduction conditions,the order of reduction ability is[C]>[Si]>[Mn]>Fe.The kinetic reaction mechanism in the direct alloying process of molybdenum oxide was studied by establishing a kinetic equation and an unreacted core model.It was found that the reduction rate of molybdenum oxide was related to its mass transfer rate and reaction area in the slag.Strengthening stirring can improve oxidation Molybdenum reduction kinetics conditions,improve the mass transfer rate of molybdenum oxide,accelerate the reduction reaction rate of molybdenum oxide.（2）The volatilization characteristics of molybdenum oxide were studied through high-temperature thermal experiments,and it was found that the volatilization rate of molybdenum oxide was mainly related to the surface area and temperature of the reaction surface.Preparing molybdenum oxide into pellets or blocks can effectively inhibit the volatilization of MoO₃.The direct alloying experiments of molybdenum oxide and ferromolybdenum were carried out by high-temperature furnace and 70t converter respectively.The results show that the yield of Mo is high and stable when the direct alloying of molybdenum oxide is used to smelt 42CrMo steel,with an average yield of96.81%.The best time to add molybdenum oxide is to add molten steel during the tapping process.（3）The microstructure composition of 42CrMo steel smelted by direct alloying of molybdenum oxide and ferromolybdenum was compared by OM,SEM and other characterization methods.The results show that:compared with the traditional molybdenum-iron alloying process,the microstructure of 42CrMo steel smelted by molybdenum oxide direct alloying process is finer and more uniform,the degree of grain refinement is higher,and the molybdenum element is evenly distributed in the matrix without obvious.The segregation phenomenon;the content of oxide inclusions in steel is less and evenly distributed.The direct alloying process of molybdenum oxide can improve the structure performance and inclusion shape of 42CrMo steel,and improve the comprehensive performance of steel.