Thermodynamics of Nitrogen Solubility and Nitride Formation in Fe–Cr–Ti–Al–Si–N Alloy Melts

Abstract

Thermodynamic behavior of nitrogen in Fe-Cr-Ti-Al-Si-N alloy melts was investigated by measuring the nitrogen solubility and solubility product of TiN and AlN by the metal/gas and metal/nitride/gas equilibration techniques at 1 823-1 873 K, respectively. The nitrogen solubility data measured in Fe-Cr-Ti, Fe-Cr-Si, Fe-Ti-Al and Fe-Cr-Al alloy melts was thermodynamically analyzed to determine the second-order cross-product parameters of Cr-Ti, Cr-Si, Al-Ti and Cr-Al on nitrogen in liquid iron using Wagner's formalism. By considering the cross-product effect on nitrogen determined in the present study, the effects of the alloying elements on the solubility product of TiN and AlN in the multicomponent Fe-Cr-Ti, Fe-Ti-Al and Fe-Cr-Al alloy melts were successfully reproduced over the wide temperature range.

Formation of Nitride and Oxide Inclusions in Liquid Fe‐Cr‐Ti‐Al Alloys

“…Thus, from the change of the TiN solubility product, the specific effect of Cr on Ti in liquid iron can be determined. In the authors’ recent study, [ 9 ] the specific effect of Cr on Al in liquid iron was also determined by measuring the AlN solubility product with the addition of Cr. The accuracy of these thermodynamic relations between the alloying elements (e.g., Cr–Ti and Cr–Al) is very important because they can also be used to describe the effect of Cr on the deoxidation equilibria in liquid iron alloys.…”

“…In the systems containing N, the N solubility and solubility product of TiN and AlN have been measured in Fe–Cr–Ti–Al–N melt over a wide range of melt composition and temperature. [ 9–11 ] The simultaneous effects of two different alloying elements on the N solubility were determined from the experimental results, and the reproducibility of the N content was improved in the multicomponent system by considering the cross‐product effect. [ 9 ] Meanwhile, for the O containing systems, the deoxidation equilibria in Fe–Cr–Ti–Al–O melt have been measured to determine the thermodynamic relation between alloying elements and O in liquid iron.…”

“…[ 9–11 ] The simultaneous effects of two different alloying elements on the N solubility were determined from the experimental results, and the reproducibility of the N content was improved in the multicomponent system by considering the cross‐product effect. [ 9 ] Meanwhile, for the O containing systems, the deoxidation equilibria in Fe–Cr–Ti–Al–O melt have been measured to determine the thermodynamic relation between alloying elements and O in liquid iron. [ 12 ] However, it was thermodynamically analyzed only recently due to the complexity of the O behavior in liquid iron alloys.…”

“…However, the Ti deoxidation experiments (Figure 1b) [ 14–20 ] are significantly scattered compared with the data measured under the TiN saturated condition (Figure 1a). [ 13,21–23 ] Therefore, in the authors’ recent study, [ 9 ] the interactions between alloying elements such as Cr‐Ti, Cr‐Al, and Al‐Ti have been determined by the relatively stable metal/nitride/gas equilibrium results. These specific parameters should be compatible with the same base alloy system regardless of the impurities, so they were applied to describe both nitride and oxide formation in Fe‐Cr‐Ti‐Al alloy melts.…”

“…Thermodynamic parameters selected from the authors’ recent studies [ 9–14,24,25 ] and previous reports [ 26–30 ] are listed in Table 1 for the multicomponent Fe–Cr–Ti–Al–N–O system. The present study carried out the verification experiments in the Fe–Cr–Ti–Al–N and Fe–Cr–Ti–Al–O systems, respectively, for checking the validity and compatibility of the parameters.…”