Effect Of Magnesium Treatment On The Inclusion And Microstructure Properties Of 30CrNi2Mo VA Steel

30CrNi2MoVA steel is a kind of alloy structure steel,which is often used to manufacture the core components of oil field fracturing machine-fracturing pump valve box.So when it works,a good comprehensive mechanical performance was important.30CrNi2MoVA steel tend to form Widmanstatten microstructure in the forging process with high temperature,and showed strong genetic and hereditary grain boundaries during subsequent heat treatment,resulting in lower mechanical properties.In the experiment the nickel magnesium alloy with low magnesium content was used as a carrier of magnesium,thereby reducing the intensity of reaction in liquid steel after adding magnesium,then to improve the yield of magnesium.The experimental results show that magnesium treatment on inclusions in steel can lead to obvious dispersion refinement of inclusions.In the experiment,before magnesium treatment,inclusions diameter mostly in more than 2 ?m,the inclusions diameter after magnesium treatment decreased to about 1 ?m,with the magnesium content in the steel improved,the proportion of the inclusions in steel below 1.5 ?m will increase from 84.04%to 93.65%,but in the same time,there will be a small amount of large size inclusions.Combined with the thermodynamic calculation,with the increase of magnesium content in steel,Oxide transformation behavior is:Al2O3?MgO Al2O3?MgO,sulfide transformation behavior is:MnS?Mg-O-S?MgO.The experimental results show that magnesium can make good effect in deoxidation,and the effect of desulphurization and dephosphorization.Through the research on the microstructure of the steel and carbide in the experiment,we found with the magnesium content in the steel increases,the microstructure of the steel was fine.Meanwhile,the carbide will be obviously refined,and the strength and toughness of the steel can be improved at the same time.From studying the effect of magnesium treatment on the microstructure of forging,magnesium can refine the forging microstructure,ferrite formation induced by intragranular,inhibit the formation of Widmanstatten structure in steel.To study the tissue after heat treatment,magnesium treated steel austenitizing time significantly later than the steel without magnesium treatment.Furthermore,the microstructure of magnesium treatment the steel is more refined.When study the tensile properties of steel,we found magnesium treatment can increase the strength of the steel while ensuring the toughness.