Experimental Research On The Calcium Treatment Of 38CrMoAl High Aluminum Steel

With the development of metallurgical technology,the calcium treatment is playing an increasingly important role in steel production.Although calcium treatment technology was used into practical very early,for how to be more precise to control of it in order to better application in production,it has always been a worthy problem to be explored for metallurgical workers.Meanwhile,the problem that behavior of volatile element Ca in liquid steel refining process is rare studied,and many researchers have different opinions on the modification mechanism of MgO·A12O3 spinal inclusions by calciulm treatment.This article will mainly analysize the modification effect of inclusions during 38CrMoAl high aiuminum steel calciulm treatment under the normal and 2.0 MPa pressure,which combined with thermodynamics calculation.Meanwhile,the modification mechanism of MgO· A12O3 spinal inclusions by calciulm treatment is discussed furtherly.Finally conclusions are drew as follows:Through thermodynamic calculation,it's found that when dissolved calcium content in steel is 0.0469%to 0.158%,A12O3 inclusions would be modified into liquid calcium aluminates,and only when w[S]in the liquid steel is less than 0.0009%,CaS wouldn't be formed in molten steel.With the increase of smelting pressure,the yield of calcium presents increasing trend basicly.Along with the increase of pressure,the highest yield is 14.6%in iron liquid and 17.3%in liquid steel under the pressure of 2.0 MPa,but under the normal pressure,the calcium yield is only 3.57%in iron liquid and 2.23%in liquid steel,thus it found that pressure can increase the yield of calcium in liquid iron.By comparing calcium treatment effects under normal pressure and 2.0 MPa,the average diameters of inclusions are increasing,but the number of unit area inclusion are decreasing with the increase of calcium content compared with inclusions in samples without calcium treatment.In CaO-MgO-A12O3 and CaO-A12O3-CaS ternary phase diagram,it is found that when dissolved calcium content in liquid steel is 0.050%under normal pressure and it is 0.058%under 2.0 MPa,most of inclusions in molten steel are modified into liquid calcium aluminate inclusions.Through SEM results of typical inclusions and thermodynamic calculation,modification mechanism of MgO·Al2O3 spinal inclusions by calciulm treatment is discussed.It's found that the dissolved calcium in the liquid steel will be priority to react with A12O3 of MgO·Al2O3 spinal inclusions,the equation is as follows:[Ca]+(x + 1/3)(MgO.Al2O3)=(CaO.xAl2O3.yMgO)+(x-y+1/3)(MgO)+2/3[Al]Under the condition that there is a certain amount of calcium in liquid steel and the reaction time is enough,MgO·Al2O3 spinal inclusions would be modified into CaO-A12O3 or CaO-MgO-Al2O3 with homogeneous composition.However,inclusions may be modified into homogeneous CaO-MgO eventually whose melting point is 2370,and solid in liquid steel with excessive calcium content.Therefore,the adding amount of calcium should be reasonable controlled to achieve the ideal effect during calcium treatment.