Yoshiyuki Ueshima

Analysis of solute distribution in dendrites of carbon steel with δ/γ transformation during solidification

Solute distribution in dendrites during solidification of carbon steel was analyzed by unidirectional solidification experiments and mathematical analysis. The characteristic of the mathematical analysis is that diffusion of solutes in solid and redistribution of solutes at solid/liquid andδ/γ interfaces are taken into consideration. Based on the observed and calculated results, it was found that phosphorus was redistributed fromγ-phase toδ-phase, and that manganese was slightly redistributed fromδ-phase toγ-phase. Therefore the concentrated region of phosphorus can be separated from that of manganese duringδ/γ transformation in the case of slow cooling. Moreover, it was concluded that rapid diffusion inδ-phase and the redistribution duringδ/γ transformation played an important role in the variation of the interdendritic concentrations of solutes with lower carbon concentration.

Precipitation behavior of MnS during δ/γ transformation in Fe−Si alloys

The precipitation behavior of MnS after solidification was analyzed with low-carbon Fe−Si alloys. This system was chosen since it has a wide temperature range for the δ/γ transformation. Experimental results showed that the amount of MnS precipitates increased drastically between 1300°C and 1100°C, and MnS precipitates were segregated almost entirely in the δ phase. This result was interpreted quantitatively by a mathematical model, taking into account the diffusion and the redistribution of solute elements and also the solubility product limit of Mn and S in both phases. Mathematical analysis shows that the precipitation of MnS starts first in the γ phase, but its growth will be very limited because of slow diffusion of Mn in the γ phase. The effects of some factors such as cooling rate and Si content of alloys on the rate of precipitation were discussed, and the degree of contributions of diffusion of Mn and the redistribution of S were estimated.

Effect of Molten Steel Flow on Nonuniformity of Initially Solidified Shell

The effect of swirling flow in the horizontal direction on the nonuniform growth of a solidified shell was investigated by dip testing the rotating cylindrical chill block. The thickness nonuniformity of the solidified shell decreases with increasing flow velocity of the molten steel. The forced flow of the molten steel increases the average heat transfer coefficient between the molten steel and the solidified shell, equalizes the growth directions of the dendrites, stabilizes the direction and intensity of the heat flux, and evens the formation of solidification nuclei.

Dissolution Behavior of Calcium into Molten Steel

Abstract In order to obtain a better understanding of the dissolution behavior of calcium into molten steel, laboratory-scale experiments and plant tests were performed. The dissolution ratio of calcium in the molten steel clearly depended on the nickel concentration in the steel. The experimental results were consistently explained using a model calculation that takes into consideration the interatomic forces between calcium, silicon, iron, and nickel inside the boundary layer around the calcium alloy during dissolution. The critical pressure of calcium required for vaporization in molten steel was also evaluated.