Papers by Author: Shuang Jiang Li

Abstract: Micron, sub-micron and nanometer sized MgO•Al2O3 ultra-fine powders were prepared by gel precipitation, solid-phase synthesis, sol-gel and flame throwing pyrogenation methods. XRD analysis showed that all of the ultra-fine powder is pure with the single MgO•Al2O3 spinel phase. The powder size was measured by laser granularity analyzer and the average size is 1780, 505 and 60 nm with a quite uniform distribution of particle size. MgO•Al2O3 spinel powder with different granularity were sprayed into molten low carbon steel in MgO crucible and MoSi2 furnace at 1873 K. Quantitative microscopic examination showed that big particle inclusions reduce and small particle inclusions increase, as a result, the average size reduce. Data comparison from spraying powders with different size showed that spraying MgO•Al2O3 of nanometer tends to cause more small inclusions in molten steel. The sprayed steel samples were rolled and heat treated for the mechanical properties tests, which showed spraying nanometer MgO•Al2O3 is the best way to improve mechanical property of steel.

Abstract: The effects of deoxidization and wire feeding operation on the type of titanium, magnesium and aluminum spinel compound inclusion were investigated in 409L stainless steel production process. Further, the formation mechanism of the compound inclusion was also researched at the same time. The results show that the spherical compound inclusion formed in molten steel presents clearly hierarchy after Ti injection in VOD refining process, where the inclusion size is about 5μm to 10μm. The MgO-Al2O3-TiO2 phase of compound inclusion presents regular configuration. MgO and Al2O3 content in compound inclusion decreases gradually together with CaO and TiO2 content increasing from interior to exterior of inclusion. The biphase structure of MgO·Al2O3-TiO2 will be formed with TiO2 dissolving into MgO·Al2O3. On the condition that Ti content is controlled at 0.25 wt.% together with w(Al)<0.01 wt.%, TiO2 solubility is generally less than 20 wt.% in MgO·Al2O3-yTiO2, as y< 0.44.