Thermodynamic Study on Deoxidation Equilibrium of High Alloyed Steel

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Demand for high alloyed steel such as Fe-Ni based alloy, ferrite-and austenite-stainless steel is increasing year by year due to the expansion of the market of advanced electronic materials. For the production of such high purity alloyed steel, it is necessary to control/or minimize non-metallic inclusion in steel products formed during the deoxidation process. A number of investigations have been done on the deoxidation equilibria in conventional low alloyed steel. However, thermodynamic knowledge on the deoxidation equilibria in high alloyed steel is very poor. The objective of the present work is to establish thermodynamic information on the deoxidation equilibria in high alloyed steel containing Ni and Co. In 1995, equilibrium among Mn-Si-O in high manganese steel (<20mass%Mn) was first investigated at MnO saturation in the temperature range from 1550ﾟC to 1650ﾟC.It was found that equilibrium oxygen content at high Mn content can not be predicted by using reported interaction parameter, and thermodynamic parameters were re-assessed based on the present experimental results. In 1996, deoxidation equilibria of Al, Ca, Mg, Zr in liquid Fe-Ni-Co alloys were studied. Interaction parameters, deoxidation products and equilibrium constants were determined as a function of temperature. Phase stability of spinel non-metallic inclusion (MgO・Al_2O_3), which is one of the most harmful inclusion, was also predicted in the present work.