76 research outputs found
An Evaluation of the Fe-N Phase Diagram Considering Long-Range Order of N Atoms in γ'-Fe4N1-x and Δ-Fe2N1-z
The chemical potential of nitrogen was described as a function of nitrogen content for the Fe-N phases α-Fe[N], γ'-Fe4N1-x, and Δ-Fe2N1-z. For α-Fe[N], an ideal, random distribution of the nitrogen atoms over the octahedral interstices of the bcc iron lattice was assumed; for γ'-Fe4N1-x and Δ-Fe2N1-z, the occurrence of a long-range ordered distribution of the nitrogen atoms over the octahedral interstices of the close packed iron sublattices (fcc and hcp, respectively) was taken into account. The theoretical expressions were fitted to nitrogen-absorption isotherm data for the three Fe-N phases. The α/α + γ', α + γ'/γ', γ'/γ' + Δ, and γ' + Δ/Δ phase boundaries in the Fe-N phase diagram were calculated from combining the quantitative descriptions for the absorption isotherms with the known composition of NH3/H2 gas mixtures in equilibrium with coexisting α and γ' phases and in equilibrium with coexisting γ' and Δ phases. Comparison of the present phase boundaries with experimental data and previously calculated phase boundaries showed a major improvement as compared to the previously calculated Fe-N phase diagrams, where long-range order for the nitrogen atoms in the γ' and Δ phases was not accounted for
Low-Temperature Nitriding of Deformed Austenitic Stainless Steels with Various Nitrogen Contents Obtained by Prior High-Temperature Solution Nitriding
Effect of Plastic Pre-straining on Residual Stress and Composition Profiles in Low-Temperature Surface-Hardened Austenitic Stainless Steel
On the nitrogen-induced lattice expansion of a non-stainless austenitic steel, Invar 36Âź, under triode plasma nitriding
Chromium, as a strong nitride-forming element, is widely regarded to be an âessentialâ ingredient for the formation of a nitrogen-expanded lattice in thermochemical nitrogen diffusion treatments of austenitic (stainless) steels. In this article, a proprietary âchrome-freeâ austenitic iron-nickel alloy, InvarÂź 36 (Fe-36Ni, in wt pct), is characterized after triode plasma nitriding (TPN) treatments at 400 °C to 450 °C and compared with a âstainlessâ austenitic counterpart RA 330Âź (Fe-19Cr-35Ni, in wt pct) treated under equivalent nitriding conditions. Cr does indeed appear to play a pivotal role in colossal nitrogen supersaturation (and hence anisotropic lattice expansion and superior surface hardening) of austenitic steel under low-temperature (â€â450 °C) nitrogen diffusion. Nevertheless, this work reveals that nitrogen-induced lattice expansion occurs below the nitride-containing surface layer in Invar 36 alloy after TPN treatment, implying that Cr is not a necessity for the nitrogen-interstitial induced lattice expansion phenomenon to occur, also suggesting another type of ÎłN
Modelling nitriding of iron: From thermodynamics to residual stress
The present article presents a few selected aspects of the modelling of gaseous nitriding of
pure iron. After descriptions of the thermodynamics of the gas phase and the reactions at the gas/solid
interface, a model description of the thermodynamics of
is given, which
takes the long-range ordering of nitrogen atoms into account. Subsequently, the kinetics of nucleation
and growth of iron nitride layers is described in terms of the rates of the surface reactions and solid
state diffusion. Thereafter, the mechanisms of stress generation in
layers during
nitriding are summarized. Finally, the model for stress development in
layers is
compared with published experimental work
Microstructural and compositional Evolution of Compound Layers during Gaseous Nitrocarburizing
In situ investigation of the martensitic transformation in Fe 12 wt. Ni 0.6 wt. C steel at subzero temperatures
In Situ Investigation of the Evolution of Lattice Strain and Stresses in Austenite and Martensite During Quenching and Tempering of Steel
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