Solubility of Nitrogen in Liquid Ni, Ni–Nb, Ni–Cr–Nb, Ni–Fe–Nb, and Ni–Cr–Fe–Nb Systems

Abstract

By means of sampling methods, we have determined the solubility of nitrogen in liquid Ni, Ni-Nb, Ni-Cr-Nb, Ni-Fe-Nb, and Ni-18Cr-17Fe-5.2Nb systems within the temperature range from 1 773 K to 1 873 K and with the niobium content from 5 to 20 mass%. It has been found that Sieverts' formalism successfully describes the solubility of nitrogen in all these liquid alloys up to 7 atm of the nitrogen partial pressure. Niobium addition increases the nitrogen solubility and its effect to increase nitrogen solubility is only second to chromium. Furthermore, we have derived the enthalpy and entropy of dissolution of nitrogen in these liquid alloys, determining the first order interaction parameter, e N N Nb (). i, 1873 K 0 0785 , up to 20 mass% Nb in nickel between nitrogen and niobium. In addition, the effects of alloying elements on the activity coefficient of nitrogen have been further investigated and the second order cross-interaction parameters between nitrogen and chromium or iron with niobium at 1 873 K have been determined as r N N

Influence of Nickel on Niobium Nitride Formation in As-Cast Stainless Steels

“…A change in the chemical composition of the solution changes the Gibbs free energy of the system and the activity coefficient of the elements. The change of Gibbs free energy of the alloy due to nitrogen dissolution, ∆G alloy N , is provided by Equation (4) [10]:…”

“…is the change of the enthalpy in the alloy due to nitrogen dissolution, ∆S alloy N is the change of the entropy in the alloy due to nitrogen dissolution, and T is the temperature in Kelvin. According to Wagner's formalism, the activity coefficient of an element, in our case nitrogen, can be written as [10][11][12][13][14]:…”

“…Tables 2 and 3 summarize the values of e i N and r i N for selected elements at 1873 K [13]. In Tables 4-6 are listed the values of e i N , r i N , and r i,j N for the Fe-Cr-Ni-Nb system [10]. 3.…”

“…As the temperature decreases, the solubility of niobium and nitrogen decreases, and the Gibbs free energy of NbN formation decreases, leading to nitride precipitation. Nitride formation occurs when the concentration of the elements is above the equilibrium solubility product curve [10]. According to Equation ( 12), the effect of chromium and nickel addition on the solubility product of niobium and nitrogen in the steel alloy at 1773 K was calculated, 1773 K being in the range of the liquidus and solidus temperatures of the investigated stainless steels.…”

“…The formation of primary nitrides depends on the chemical activity of nitrogen and niobium in the steel melt and during solidification. The presence of nickel lowers the solubility of nitrogen in the steel melt [10]. Nickel is a common alloying element in SS; it is especially important in ASS, where the contents are around 10 wt.%.…”