Effects of Electro-fused Magnesia on Properties of Al_2O_3-SiC-C Castable

Al2O3-SiC-C castables for iron trough with fused magnesia powder （0, 3%, 6%, 9% and 12%） were prepared with brown fused corundum particles （5-3mm, 3-1mm, ≤1mm）, white fused corundum powder （≤0.088mm）, SiC particle （≤1mm） and powder （ ≤0.088mm）, fused magnesia powder （ ≤0. 088mm）, reactive α-Al2O3 micropowder, ultrafine SiO2 , Si powder and sphere pitch as main starting materials and calcium aluminate cement as binder. The specimens were fired at 1100℃ and 1450℃ for 3 h after vibrating moulding, curing, demoulding and drying at 110℃ for 24 h. Bulk density, apparent porosity, linear change rate, modulus of rupture, resistance to blast furnace slag, oxidation resistance, phase composition and microstructure of the specimens were analyzed. The results show that： （1） With fused magnesia addition increasing, apparent porosity increases, while bulk density, modulus of rupture and oxidation resistance decline, slag resistance varies slightly; （2） The main crystal phases in the specimens fired at 1450℃ for 3 h are 3C-SiC, 6H-SiC, corundum, periclase, reaction-synthesized spinel and mullite; the quantity of the formed spinel and mullite increases with the increase of fuzed magnesite addition; （3） Along the corroded side, spinel layer with about 80μm thickness forms at the co- rundum particles boundary.

Indispensability and Vulnerability of Magnesia-carbon Bricks for Steelmaking Process

The manufacturing techniques of magnesia-carbon bricks in China have been documented from raw materials,production(process and facilities)to performance and wear issues in the ladle.Magnesia-carbon bricks made of ordinary fused magnesia is the prevailing material used in the slagline of the ladle,but its service life is substantially lower than the bricks based on large-periclase-crystal fused magnesia.In two types of fused magnesia,the average values of periclase crystal size are in double for their difference.It is suggested that large-periclase-crystal fused magnesia should be used for manufacturing magnesia-carbon bricks for the slagline of the ladle by abandoning ordinary fused magnesia,in order to have a prolonged service life,increase the availability of the ladle and reduce the number of downtimes of the ladle.Free phenol in resin produced in China should be as low as that of resin made in Europe,to improve production environment and reduce smoke emission during the ladle preheating.There are large spaces to promote the productivity of magnesia-carbon bricks in China,with high intensity mixers and hydraulic presses.Expansion controlled magnesia-carbon bricks in the ladle depend on the optimized combination of sintered magnesia,Carbores and antioxidants as the matrix,to minimize the premature wear of vertical cracks and joint opening formed in the ladle lining.

Influence of Microporous Magnesia-rich Spinel Aggregates on Properties of Low Carbon MgO-C Refractories

Two types of low carbon MgO - C refractories with 6% graphite were prepared using microporous magnesiarich spinel （5 - 3 and 3 - 1 mm ） and fused magnesia （5 - 3 and 3 - 1 mm ） as coarse aggregates, respectively, fused magnesia （ ≤1 mm） as fine aggregate, magnesia powder （≤ 0. 088 mm ） , flake graphite powder （ ≤0. 088 mm）, metal Al powder （ 〈0. 074 mm） as matrix, and phenol resin as binder. After curing at 220 ℃ and coke-embedded firing at 1 500 ℃ , the apparent porosity, cold crushing strength, cold modulus of rupture, permanent linear change on heating, thermal shock resistance and slag resistance of the specimens were studied comparatively. The results indicate that： （ 1 ） after curing at 220 ℃ and coke-embedded firing at 1 500 ℃, the specimen with microporous magnesia-rich spinel replacing fused magnesia has lower bulk density and higher apparent porosity than the common low car- bon MgO - C specimen. After curing at 220 ℃, the specimen with microporous aggregate has lower strength than common low carbon MgO - C specimen, but after coke-embedded firing at 1 500℃, it has higher strength and lower permanent linear change on heating; （2） low carbon MgO - C specimen using microporous magnesia-rich spinel to replace fused magnesia aggregate has better thermal shock resistance but worse slag resistance.

Interaction between microporous magnesia castable and 38CrMoAl steel

The microporous magnesia refractory shows a promising application prospect as tundish lining due to excellent thermal insulation and slag resistance.The effect of interaction between microporous magnesia castable and 38CrMoAl steel containing 0.876 wt.%Al on the cleanliness of 38CrMoAl steel was studied and compared with that of fused magnesia castable.The results show that the micropores in the microporous magnesia castable can promote the formation of dense and continuous MgO-Al_(2)O_(3)layer,which can inhibit the further pollution of molten steel by refractories,whereas the MgO-Al_(2)O_(3)layer formed in test of fused magnesia castable is not continuous.After 30 min holding,the total oxygen content in the steel samples for the test of microporous magnesia castable is only 42.2%of that for the test of fused magnesia castable.The inclusions in the steel samples for the test of microporous magnesia castable are also less than those for the test of fused magnesia castable.It shows that microporous magnesia castable is a promising tundish refractory for the preparation of clean high-Al steel.