Study On The Effect Of A1 Or A1/Zn Addition On The Microstructure And Properties Of Ultra-low Carbon MgO-CaO-C Refractory

With the improving quality and the demand quantity of clean steel, the requirements of refractories for ladle refining are more and more highly. As we know, the steel liquid can be purified by basic refractories especially MgO-CaO-C materials. But MgO-CaO-C materials used at present contain too much carbon(C≥8wt%), which has bad effect on steel purifying. So it is significantly important to study metal containing ultra-low carbon MgO-CaO-C material s(C≤3wt%). In this work, ultra-low carbon MgO-CaO-C materials were prepared using sintered magnesia-calcium clinker, fused magnesia and Al powder. The effect of Al and Al /Zn addition on ultra-low carbon MgO-CaO-C materials was inspected. The physical properties, hot modulus of rupture(HMOR), thermal shock resistance(TSR) and oxidation resistance of synthesized MgO-CaO-C materials were researched, also the relation of structure and property was investigated.The HMOR(1400℃) and the residual strength(△T=1100℃, air-cooling three times) of ultra-low carbon MgO-CaO-C materials can be significantly improved by adding Al powder. The HMOR of specimens improved by 2 to 4.6 times and the residual strength improved by 0.5 to 1.7 times after Al addition. The residual strength ratio maintains at a high level(≥66%). Also, oxidation resistance of specimens containing Al powder is improved remarkably. Compared with complete oxidation of carbon in specimens without Al powders at 1000℃and 1500℃, the oxidation resistence of specimens with Al content is quite good and with the Al content increasing, the thickness of oxiditation layer becomes thinner.Based on 4wt% Al addition, the HMOR of specimens can be significantly improved furtherly by 1 to 1.8 times with the adding of Zn into ultra-low carbon MgO-CaO-C materials. But the HMOR of specimens increases very slightly when the addition of Zn exceeded 1%. The residual strength increases by 0.7 to 1.7 times with the increasing of Zn content and the residual strength ratio maintains at about 87%. The oxidation resistance at 1000℃and 1500℃is also improved as the result of the addition of Zn. The thickness of oxidation layer is gradually attenuated from 2mm to 0.3mm.The improvement of the performence with 2% graphite and carbon black addition on ultra-low carbon MgO-CaO-C materials is not obvious compared with only 4wt% Al and 1% Zn addition.Together with the analysis of XRD and SEM, it can be seen that non-oxide materials Al4C3、AlN are in-situ synthesized by the reaction of Al, C and N2 in the heating process with carbon embedding. The non-oxide materials fill in the skeleton structure of MgO and CaO and creat the bonding, which would strengthen and toughen the structure, furtherly increase the mechanical properties of these composites at high temperature. The reason why the oxidation resistance of ultra-low carbon MgO-CaO-C materials with Al and Al/Zn addition is superior is that the addition of Al leads to the generation of some oxidation products such as in-situ spinel, which would form protective layer to prevent O2 from infiltration. Also, Zn is characterized with high activity, which can catalyze the in-situ reaction.