Jong-Jin Pak

Nitrogen solubility in high manganese-aluminum alloyed liquid steels

The nitrogen solubility in liquid Fe-Mn and Fe-Mn-Al alloys has been measured by the gas-liquid metal equilibration technique utilizing a high frequency induction furnace under the nitrogen partial pressures of 0.1 to 0.8 atm in the temperature range of 1773 to 1873 K. The variation of the nitrogen solubility with the addition of manganese was measured by sampling and in-situ analysis of nitrogen content. Manganese significantly increased nitrogen solubility in liquid Fe-Mn and Fe-Mn-Al alloys. The nitrogen dissolution followed the Sieverts’ law for liquid Fe-Mn alloys contained manganese up to 26 mass%. Using the Wagner’s interaction parameter formalism, the experimental results were thermodynamically analyzed to determine the first- and second-order interaction parameters of manganese and aluminum on nitrogen in high Mn-Al alloyed liquid steels. No temperature dependence of these values was observed in the temperature range of 1773 to 1873 K. eNMn = −0.023, rNMN = 0 rNMn,Al = 0 (Mn≤26 mass%, Al≤0.4 mass%, 1773–1873 K).

In Situ Observation on Behaviors of CaO-MgO-Al2O3-SiO2 Complex Inclusions at Solid–Liquid Interface of Low-Oxygen Special Steel

The movements of CaO-MgO-Al2O3-SiO2 inclusions at solid–liquid (S–L) interface during the solidification of low-oxygen special steel were observed in real time by the confocal laser scanning microscope, in an attempt to explore the possible formation mechanism of the D-type and DS-type inclusions. It was found that S–L interfaces showed strong interaction with the inclusions, especially when the inclusions were captured. Collision and agglomeration between inclusion in liquid steel and inclusion captured by the S–L interface were reproducibly observed, followed by an obvious size growth. During this process, inclusions in liquid steel acted as the guest particles, while the S–L interface capture inclusions acted as the host particles. There were also inclusions first moved toward and then later away from the S–L interfaces. To explain the behaviors of inclusion pairs, the forces acted on inclusions were estimated and discussed. Based on the obtained result, it can be cautiously pointed out that collision and agglomeration of inclusions at S–L interface during the casting of steel are probably important reasons for the frequent existence of D-type and DS-type inclusions during the production of low-oxygen special steel despite the high cleanliness. Therefore, minimization of inclusion size is significant except for the reduction of the inclusion numbers.

Nitrogen Solubility in Liquid Mn-Fe-Si-C Alloys

The nitrogen solubility in liquid Mn-Si, Mn-Si-Fe, Mn-Si-C and Mn-Si-Fe-C alloys has been measured by the gas-liquid metal equilibration technique in the temperature range of 1673–1773 K. The additions of silicon, iron and carbon significantly decreased the nitrogen solubility in liquid manganese alloys. The experimental results were thermodynamically analyzed by the Wagner’s formalism to determine the first- and second-order interaction parameters of silicon, iron and carbon on nitrogen in liquid manganese. The thermodynamic parameters can be used to predict the nitrogen solubility in ferromanganese and silicomanganese alloy melts as functions of the melt composition and temperature at given nitrogen partial pressures.

Thermodynamic Optimization of Mn‐Si‐C System

The critical evaluation and thermodynamic optimization of Mn-Si-C and its sub-binary systems have been carried out over the whole composition range from room temperature to above the liquidus temperature. The solution properties of the liquid systems have not been clearly described because the liquid solution exhibits a high degree of short-range-ordering. In order to predict the thermodynamics of the liquid solution, the liquid phases were optimized by the modified quasichemical model. The model parameters of the solid phases were also optimized by the compound energy formalism to best reproduce the phase diagram and important thermodynamic properties in Mn-Si-C system. Using the model parameters, various thermodynamic calculations were carried out. The present database will be a part of larger thermodynamic database for the ferromanganese alloy database.