The graph shows the solubility of nitrogen in expanded austenite (γN) as a function of the imposed nitrogen activity (aN) in a gas mixture of NH3 and H2 for the stainless steels and temperatures indicated in the legend.
Fully nitrided and denitrided conditions are indicated by aN = ∞ and aN = 0, respectively. The master curve can be applied for estimating the surface content of nitrogen for a gas mixture of known nitrogen activity aN = K(T) · K, with K(T) the temperature-dependent equilibrium constant of ammonia dissociation.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Low-Temperature Surface Hardening of Stainless Steel ⇒ Physical Metallurgy of Expanded Austenite
