| Since the 1970s,MgO-C refractories have been rapidly developed due to their good slag resistance and thermal shock,and are widely used in the steel metallurgy industry as work lining in converters,electric furnaces,refining furnaces and ladles.However,the refractories have two major problems in use process,one is that carbon of the refractories is oxidized easily and the other is that decarburization layer has loose structure and poor anti-erosion ability.Therefore,we usually add antioxidants in MgO-C refractories to inhibit the oxidation of carbon,such as Al Si Mg etc.Although the introduction of antioxidants can effectively improve its antioxidant properties,the decarburization layer of high temperature mechanical properties is very limited.When the decarburized layer off,it will cause accelerated deterioration of refractory properties,affecting its service life.To solve this problem,this paper presents a new concept of using Fe powder to enhance the toughening of MgO-C refractory based on ptimizing decarburized layer microstructure and sinterability.And stuied the effect of fe addition on the microstructure,high temperature oxidation behavior and high temperature mechanical properties of MgO-C refractory,through the combination of thermodynamic analysis and high temperature experiment.And the following important research results are obtained:(1)The addition of Fe powder has the function of zoning regulation on the microstructure of MgO-C refractory.On the condition of high temperature(1300℃～1600℃),due to the affinity between iron and oxygen is less than carbon,Fe particles can stably exist in the original layer and act the binder phase.In this way,the magnesite combination mode is changed from simple "carbon-bonded" to "carbon+metal".In the decarburized layer,Fe powder is oxidized completely and finally transformed into Mg(Fe,Al)2O4,which connects the isolated matrix particles tightly.prompts the decarburization layer to be transformed from an isolated and dispersed simple structure to a complex network structure.In addition,the solid solution of a large number of iron oxides in magnesia matrix could enhance the sintering activity effectively,thereby further enhancing the degree of direct bonding between particles(2)The addition of Fe power can solve the problem of serious deterioration of structure and properties effectively.After heating at 1600℃ for 3h in air,the decarburization layer of traditional MgO-C refractories showed loose porous structure with low bond,and the density and compressive strength decreased by 15.6%and 35%respectively.After adding 12wt%Fe,the improvement of sintering activity and the formation of Mg(Fe,Al)2O4 high temperature combination phase could promote the densification of the decarburization layer and improved its bonding strength.After oxidation treatment,the density and compressive strength decrease by 11.2%and 7.1%respectively.(3)The addition of Fe powder can increase the antioxidant properties of MgO-C refractories significantly.The carbon oxidation life of MgO-C refractories with 12wt%Fe increased from 1044min to 4141 min.which increased by nearly 3 times.The fundamental reason for the increase of the oxidation resistance is the decrease of porosity,the increase of internal structure tortuosity and the increase of gas diffusion resistance caused by the increase of MgO dense layer thickness.(4)The addition of Fe powder kept the higher load softening temperature of the MgO-C refractories.Due to the high melting point and low impurity content of fused magnesite and graphite,refractoriness under load was 1679℃,which was up to 1690℃ with adding 12wt%Fe,because the stable existence of the solid metal Fe in the original layer and the increase of the high temperature binding strength of the decarburization layer.In addition,the addition of Fe powder could effectively reduce the thermal expansion coefficient of MgO-C refractories at high temperature,which is beneficial to maintain the volume stability in service.(5)The addition of Fe powder could solve the problem of poor creep resistance of MgO-C refractories in air.At 1500℃,the creep rate of traditional MgO-C refractories accelerated with the prolongation of holding time due to th e high porosity and low matrix binding strength of the decarburization layer.After constant temperature 14h,the deformation rate reached-0.34%/min and the creep rate as high as-8.1%.After addition of Fe powder,the density of decarburized layer and matrix bonding strength increased creep resistance,the deformation rate of steady state stage was only-2.2×104%/min.which could maintain the structure and stable performance long time in thermal load,and its creep rate is only-1.05%for 50h,which reflected the excellent high temperature creep resistance. |
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