Metal Composite Low-carbon High Temperature Properties Of Mg-al Carbon Materials

As a result of the development of clean steel,High quality of materials used at steel ladle linings will be an important aspenet for steel liquid.Basic refractories was beneficial to steel liquid.Therefore,it's useful to study metal containing of low-carbon MgO-Al₂O₃-C materials.Low Carbon MgO-Al₂O₃-C materials have been prepared by using fused magnesia,fused spinel,Al powder,Si powder,Zn powder and flake graphite as starting materials.Hot modulus of rupture(HMOR),thermal shock resistance(TSR),oxidation resistance and slag corrosion resistance have been studied,and phase composition and microstructure were studied by XRD, SEM and EDAX.The results showed that:1) HMOR(1400℃) can be significantly improved when Al/Si and Al/Zn powder were added into low-carbon MgO-Al₂O₃-C materials,from 3.0MPa to 23.0-32.5MPa;Specimens of ASC2(4.5%Al,2.5%Si) and A6Z1(6%Al,1%Zn) possess much higher high temperature strength than other specimens in the same series.Based on this,when SiAlON (1.5-4.5%) was added into materials HMOR can be increased from 11.5MPa to 19.6MPa; Specimens of ASN1(1.5%SiAlON) possesses much higher high temperature strength than other specimens in ASN series.2) TSR(ΔT=1100℃,air-cooling one times) can be significantly improved when Al/Si and Al/Zn powder were added into low-carbon MgO-Al₂O₃-C materials.The residual strength ratio after thermal shock was improved from 60%to 61-79%.Based on this,when SiAlON (1.5-4.5%) was added into materials,the residual strength ratio can be increased from 81% to 94%.The most significantly improved of the residual strength ratio was specimens added with Al/Zn powder.The ratio can reach 93-97%when 1-2%Al/Zn was added.3) The excellent high temperature mechanical properties of these composites may be attributed to:Al,Si and Zn react with C and N₂ in-situ formation Al₄C₃,AlN and SiC and other non-oxide which would fill in the interstrices of periclase/spinel skeleton structure creating strengthening and toughening effects at high temperature.TSR was also increased by added some SiAlON into materials because SiAlON plays a complementary role in toughening effects.4) The oxidation resistance can be significantly improved when Al/Si and Al/Zn powder were added into low-carbon MgO-Al₂O₃-C materials.The thickness of oxidized layer after oxidation tests at 1000℃for 3 hours was 5.6mm with 4.5%Al addition.Based on this, when 1.5-3.5%Si was added into materials,the thickness of oxidized layer after oxidation tests decreased to 2.9-3.4mm;Oxidation resistance would be improved with addition of 1-2%Zn powder,and the thickness of oxidized layer after oxidation tests decreased to 0.5-1.4mm.The change of the thickness of oxidized layer after 1000℃for 3 hours was the same with of 1500℃,but the latter one was much thinner.Such as specimens of AS2 (4.5%Al,2.5%Si) which thickness of oxidized layer was 1.2mm,specimens of A4Z4 (4.5%Al,2%Zn) which thickness of oxidized layer was thinner than 0.1mm.Their superior oxidation resistance may be because the oxidation products of Al,Si and Zn react with MgO to form dense spinel and M₂S protective layer retarding O₂ infiltration.More quantities of spinel and M₂S were formed at 1500℃,but a few quantities of spinel was formed at 1000℃,so the more better one was of 1500℃.5) The corrosion resistance(1600℃×3h) can be distinctly improved when Al/Si and Al/Zn powder were added into low-carbon MgO-Al₂O₃-C materials.The thickness of corrosible layer was decreased from 4.8mm to 1.2-1.9mm.Based on this,when SiAlON (1.5-4.5%) was added into materials,the thickness of corrosible layer can be decreased from 1.9mm to 1.0mm.The most significant improvement of carrion resistance was specimens added with Al/Zn powder.The thickness of corrosible layer can be decreased to 0.6-1.4mm when 1-2%Al/Zn was added.It could be expected to have good prospects when these materials were used at clean steel linings in continuous casting.