The AlN solubility product in liquid iron containing manganese up to 22 mass% were measured by the metal-nitride-gas equilibration technique in the temperature range from 1 823 to 1 873 K. Manganese significantly increased the AlN solubility product in liquid iron primarily due to the large effect of manganese on the nitrogen solubility. Using the Wagner's formalism, the experimental results were thermodynamically analyzed to determine the thermodynamic interaction parameters between manganese and aluminum in high Mn-Al alloyed liquid steels as follows;(Mn ≤ 22 mass%, Al ≤ 1.8 mass%, 1 823-1 873 K) KEY WORDS: high manganese steel; AlN; aluminum; nitrogen; interaction parameter.

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The nitrogen solubility in liquid Fe-C alloys containing carbon up to 5.2 mass% has been measured under reduced nitrogen partial pressures in the temperature range of 1 773-1 873 K. Previous studies on the C-N interaction in liquid iron have shown marked disagreement on its temperature dependency and the order of interaction. By the gas-liquid metal equilibration technique using a high frequency induction furnace with an accurate temperature measurement, precise nitrogen solubility data were obtained. The interaction between carbon and nitrogen in liquid iron has been expressed in terms of the first-and second-order interaction parameters. No temperature dependence of these values was observed in the temperature range from 1 773 to 1 873 K.(1.14 ≤ mass% C ≤ 4.95 at 1 773 K, 0 ≤ mass% C ≤ 5.2 at 1 823-1 873 K) KEY WORDS: nitrogen solubility; Fe-C alloy; carbon; interaction parameter.

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Thermodynamics of nitrogen and AlN formation in multi-component liquid iron alloys containing Mn, Al, Si and C was investigated by the metal/gas and the metal/nitride/gas equilibration techniques under reduced nitrogen partial pressures in Ar-N 2 gas mixture. The N solubility was measured in binary Fe-Mn and Fe-Si alloy melts, and ternary Fe-Mn-Si, Fe-Al-Si, Fe-Mn-C and Fe-Si-C alloy melts over wide composition range at 1 773-1 873 K. Using Wagner's formalism, the effect of alloying elements on the N solubility was described as the first-and second-order interaction parameters as well as the second-order cross-product parameters. The validity of the interaction parameters determined in the present study was checked by measuring the N solubility and AlN solubility product for a typical TWIP steel composition melt of Fe-25% Mn-0.3% Si-0.6% C-Al at 1 723-1 873 K.

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The nitrogen solubility and the AlN solubility product in liquid Fe-C-Al-N alloys containing a wide composition range of carbon and aluminum were measured in the temperature range of 1 773-1 873 K. Aluminum and carbon both decreased the nitrogen solubility in liquid iron. The simultaneous effect of aluminum and carbon on nitrogen solubility in liquid iron was determined. The AlN solubility product in liquid iron decreased significantly with carbon addition primarily due to the large effect of carbon on nitrogen solubility. Using the Wagner's formalism, the experimental results were thermodynamically analyzed to determine the interaction parameters among carbon, aluminum and nitrogen in liquid iron as follows: