Yuji Miki

Fundamental Research on a Rational Steelmaking Slag Recycling System by Phosphorus Separation and Collection

Abstract Recently, reduction of the steelmaking slag stock in Japan has been required, but utilization of steelmaking slag is restricted due to its chemical properties. On the other hand, the price of phosphorus ore is increasing rapidly due to the very tight supply/demand balance worldwide. In this work, (FetO) and (P2O5) reduction in steelmaking slag and recovery as a phosphorus source were investigated in feasibility studies and laboratory-scale experiments in order to develop a rational recycling process for steelmaking slag. The results are summarized as follows: (a) Steelmaking slag was reduced by carbon under high temperature conditions (1373–1873 K), and high-P hot metal was recovered. The phosphorus content of the reduced slag was <0.3 mass%. (b) Higher temperatures were required for slag reduction with carbon, corresponding to increasing slag basicity. (c) The oxygen partial pressure calculated from the FeO content ranged from 10−13 to 10−17 atm. More than 50 mass% of phosphorus in the slag can be removed under the condition that FeO activity is less than 0.01. (d) From the mass balance of phosphorus, 0–30 mass% of undefined phosphorus was observed, which was estimated by thermodynamic calculations and SEM-EPMA analysis to be caused by gaseous dephosphorization. (e) The gaseous dephosphorization ratio becomes more than 10% at the condition of log LP ≤  0. (f) Phosphorus was enriched in slag to higher than 30 mass% P2O5 by dephosphorization of high-P (1.05 mass%) hot metal.

Fundamental Investigation of Reduction and Dissolution Behavior of Manganese Ore at High Temperature

The high temperature reduction behavior of manganese ore was investigated with the aim of utilizing ore as a more economical manganese source in the steelmaking process. The melting temperature and phase change behaviors of raw and sintered manganese ores were measured by high temperature X-ray diffraction and DTA in the temperature range from 303K to 1773K under atmospheric and vacuum conditions. The melting temperatures of the raw and sintered manganese ores were 1688K and 1732K, respectively. The main manganese compounds in the raw and sintered manganese ores were CaMn6SiO12 and MnO, Mn3O4 respectively. Under a vacuum (0.13kPa), both the raw and sintered manganese ores were reduced to MnO above 1473K, whereas under the atmospheric condition (101.3kPa), the manganese ores were reduced to Mn3O4 rather than MnO. The obtained results were discussed from a thermodynamic viewpoint.

Effect of Electromagnetic Brake on Decreasing Unbalanced Flow in Mold

In order to clarify the mechanism of suppression of unbalanced flow in the mold under high throughput conditions in continuous casting, the effect of using an electromagnetic brake on decreasing molten steel momentum and suppressing unbalanced flow in the mold was investigated. (1) The measured value of the effect of the electromagnetic brake on decreasing molten steel momentum was consistent with the calculated value. Molten steel momentum could be reduced by more than 50% when the Stuart number was more than 3. 5. (2) Increased mold level fluctuations caused by unbalanced flow in the mold are suppressed by applying the optimum magnetic flux density with an electromagnetic brake, even under high throughput conditions.

Activities of FexO in Industrial Slags Used for External Removal of Phosphorous from Hot Metal

Abstract In order to obtain a physicochemical knowledge of complex industrial slags, the activities of FexO in the industrial slags used for external dephosphorization of hot metal performed at practical steelmaking plants in Japan were measured by means of a solid-oxide galvanic cell in a temperature range between 1523 K and 1673 K. XRD study showed the presence of solid phases in all the slags, showing the heterogeneous character of the slags employed. With respect to the effect of CaF2 on FexO activity, the FexO activities of the heterogeneous slags were correlated with the ratio X(FeO)/X(CaF2). High X(FeO)/X(CaF2) values corresponded to high FeO activity. This tendency is interpreted based on the phase relationship in a CaO-CaF2-FexO ternary system. A favorable condition for external dephosphorization with less addition of CaF2 is discussed.