Phase transformations and induced volume changes in a nitrided ternary Fe–3%Cr–0.345%C alloy

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. AbstractPhase transformations during nitriding of a ternary carbon iron-based alloy Fe-3%Cr-0.345%C were studied, aiming for a better understanding of residual stresses generation and evolution. The relationship between the precipitation of Cr 7 C 3 carbides and CrN nitrides, the induced volume change and the mechanical properties were investigated at three distinct depths of the diffusion zone. The relaxation of residual stresses arose through phase transformations according to the diffusion of nitrogen but also of carbon.

Gaseous nitriding behaviour of 33CrMoV12-9 steel: Evolution of the grain boundaries precipitation and influence on residual stress development

“…Because the nitrogen content increases at deeper depth below the surface, the effective depth is enhanced with the temperature and time of nitriding. However, the level of hardening remains lower deeply below the surface than at the close surface due to incomplete precipitation of nitrides, a lower nitrogen flux that involves growth/coarsening of existing precipitates rather than the nucleation of new ones and finally due to an increase of initial carbides according to the enrichment of carbon in front of the nitrogen diffusion front [5,13]. Figure 12 shows the in--depth residual stress profiles obtained from XRD analyses.…”

“…Due to the low volume fraction of precipitates, no X--ray analysis was performed to identified the nature of iron nitrides at grain boundaries in the present study. However, previous work concluded on the presence of (γ')Fe4N at grain boundaries at the interface between the compound layer and the diffusion zone [13]. Figure 9 gives the depth where the porous and dense layers (both defining the compound layer (see Figure 5 for instance)), iron nitrides (FexN) and a mixture of iron nitrides plus carbides (FexN +Fe3C) at grains boundaries are observed based on BSE--SEM observations and EDX analyses.…”

Determination of the volume fraction of precipitates in a nitrided Fe-0.354 wt% C-2.93 wt% Cr model alloy by anomalous small angle X-ray scattering

“…In fact, the electronic density of a phase 116 constituted by N elements can be written: In the vicinity of the absorption edge of the element k, the electronic contrast can be 122 written: 123 equation (3) and with previous studies on this material [7]. The procedure of preparing the ASAXS 225 sample from a bevel through the nitrided sample in order to perfom in---depth scanning of 226 the nitrided layer is as a consequence proven.…”

“…Gas nitriding was performed by Aubert & Duval at 550 °C during 75 100 h for a given nitrogen potential (KN = 2.65 atm -1/2 ). Composition profiles along the 76 nitride layer were carried out by electron probe microanalysis (EPMA) as well as glow 77 discharge optical emission spectrometry (GDOES) [7]. Observations of the case and core 78 microstructure were carried out by optical microscopy as well as scanning and 79 transmission electron microscopy.…”

Normal and excess nitrogen uptake by iron-based Fe–Cr–Al alloys: the role of the Cr/Al atomic ratio

“…Nitriding is a thermochemical surface-treatment process of ferritic steel components in order to improve properties such as the resistances against fatigue, corrosion and wear [1][2][3][4][5][6][7]. In order to introduce nitrogen into the component, gaseous nitriding, employing NH 3 -based atmospheres, is widely adopted.…”