Papers by Author: Ying Zhuang

Abstract: Thermodynamics software on inclusions prediction in 430 stainless steel was developed with Matlab and VC++. The inclusions’ composition could be predicted by composition of molten steel input, and equilibrium phase diagrams of MgO•Al2O3, 2MgO•SiO2, 3Al2O3•2SiO2 and 2Al2O3•2MgO•5SiO2 were displayed on the main interface simultaneously. The following predicted results by inputing experiments data at 1873 K can be gained that When Si content is 3.9×10-3and Al content is 3.5×10-4, MgO•Al2O3 spinel inclusions is unformed in case of Mg content with larger than 1.71×10-5; while MgO•Al2O3 spinel inclusions transformed into 2Al2O3•2MgO•5SiO2 inclusions in case of Mg content being less than 2.9×10-8. The predicted results of software fit well with the experiment results, Therefore, the software can provide some results for controlling the composition of inclusions in molten steel.

Abstract: The effect of the refining slag composition on the total oxygen content and inclusions in steel was investigated in 100 t UHP Electric Furnace – LF – Billet CC process. The test steel was 77B hard wire steel and Si-Mn alloy was used as the deoxidizer. Three types slag were used in the industrial tests, which including CaO-CaF2, CaO-CaF2 adding CaC and CaO-Al2O3 refining slag. The results shown that the lowest total oxygen contents of rolled bar can be gained using the CaO-CaF2 refining slag adding CaC, which is 0.0036%, while the total oxygen contents of rolled bar using CaO-Al2O3 refining slag is higher a little than the heats using CaO-CaF2 refining slag. The CaO-SiO2 and CaO-Al2O3-SiO2 compound inclusions with the size of about 5 μm are the main inclusions in the heats refining by the CaO-CaF2 refining slag in the rolled bar, but the pure, indeformable Al2O3 inclusion can also be found with the size of about 10 μm. The CaO-Al2O3-SiO2 and Al2O3-SiO2-MnO compound inclusions are the main inclusions in the heats refining by the CaO-CaF2-CaC refining slag, but most of the inclusion shape is irregular with bigger size of about 10 μm. Similar with the heat using CaO-CaF2 refining slag, the pure Al2O3 inclusion with edge angle can be found in the rolled bar. The inclusions in the rolled bar treated by CaO-Al2O3 refining slag are CaO-Al2O3-SiO2 compound inclusions, most of which are nearly globular shape with the relative small size of about 5 μm. All of the inclusions in rolled bar lie on the low melting zone in the CaO-Al2O3-SiO2 ternary phase diagram in the heats using CaO-Al2O3 refining slag. The similar condition appeared on the most of the inclusions in the heats using CaO-CaF2 and CaO-CaF2 refining slag adding CaC, while part of which are lied on the high melting zone. Therefore, considering of the plastic deformation ability, the CaO-Al2O3 refining slag is the best slag for the melting process of hard wire steel.

Abstract: The variation of non-metallic inclusions and total oxygen contents in different steel grades were investigated by taking samples in steelmaking process, including gear steel, anchor chain steel, hard wire steel, bearing steel and spring steel. The inclusions mainly were Al2O3, MnS, and their composite inclusions in aluminum killed steel at the beginning of LF refining due to addition of FeAl alloy during the tapping from EAF and feeding of Al wire in LF process, and then Al2O3 inclusion changed to the Al2O3 - CaO composite inclusions after feeding of SiCa wire. The inclusions at the beginning of LF refining mainly were MnS, SiC and their composite inclusions in non-aluminum killed steel due to addition of the composite deoxidation and slagging agents (mainly including CaC2 and SiC) when EAF taping, while the inclusions in tundish mainly were MnS, CaO - SiO2 - Al2O3 composite oxide - sulfide inclusions. It is showed that the inclusions in bearing steel and spring steel samples were mainly globular oxide inclusions and silicate inclusions with higher rated results. Therefore, the refining process should be improved to remove globular oxide inclusions. The inclusions in molten steel were controlled by enhancing the diffusion deoxidation process, adjusting and controlling the basicity and composition of refining slags, respectively, and satisfactory results were obtained. The industrial test shows that the total oxygen content of the aluminum killed steel in the test heat after feeding wire reached the minimum value, which indicates that the optimized slag has a strong ability of absorbing Al2O3 inclusions. For non-aluminum killed steel, the total oxygen content was 0.0027 % to 0.0029 % in rolled products. The inclusions in the end of refining and rolled product were small and dispersed composite inclusions, and the separate Al2O3 inclusions can not be found in the non-aluminum killed steel after optimization of the refining process.

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.