Comments on determining X-ray diffraction-based volume fractions of retained austenite in steels

Abstract

Retained austenite is an important characteristic of properly heat-treated steel components, particularly gears and shafts, that will be subjected to long-term use and wear. Normally, either X-ray diffraction or optical microscopy techniques are used to determine the volume percent of retained austenite present in steel components subjected to specific heat-treatment regimes. As described in the literature, a number of phenomenological, experimental, and calculation factors can influence the volume fraction of retained austenite determined from X-ray diffraction measurements. However, recent disagreement between metallurgical properties, microscopy, and service laboratory values for retained austenite led to a re-evaluation of possible reasons for the apparent discrepancies. Broad, distorted X-ray peaks from un-tempered martensite were found to yield unreliable integrated intensities whereas diffraction peaks from tempered samples were more amenable to profile fitting with standard shape functions, yielding reliable integrated intensities.Retained austenite values calculated from reliable integrated intensities were found to be consistent with values obtained by Rietveld refinement of the diffraction patterns. The experimental conditions used by service laboratories combined with a poor choice of diffraction peaks were found to be sources of retained austenite values containing significant bias. © 2001 International Centre for Diffraction Data.

Investigation of the 'tiger skin' defect on indefinite chill rolls

“…The XRD analysis for RA is strongly affected by alloying elements and carbides. Given the high level of alloying elements in the material it should be noted that the accuracy will be less than typically achieved by XRD (vander Voort and Manilova, 2005;Lowe-Ma and Donlon, 2001).…”

“…XRD was then done to analyse the phases present within the samples. The relative phase amounts (mass %) were estimated using the Rietveld method (Lowe-Ma and Donlon, 2001). The carbide morphologies and quantity data (as determined by microscopy) were used to ensure accurate RA peak identification to avoid erroneous overestimation.…”

Determination of Stresses and Retained Austenite in Carbon Steels by X-rays - A Round Robin Study

“…Broad distorted martensite peaks [15], metallic carbides, a strong preferred orientation of the material and improper R-values could also be considered as sources of errors in determination of the volume fraction of retained austenite. In this research work, however, the material was studied in a tempered condition and, thus, broad distorted martensite peaks were of no concern.…”

“…Regarding the theoretical R-values used, LoweMa et al [15] showed that the effect of using theoretical Rvalues in comparison to calculated values is rather small, and that this influence is inadequate for variations in measured results. However, this is only valid for low alloyed materials.…”

“…Several round robin tests have been performed by different research groups dealing with measurement of either residual stresses [13,14] or retained austenite content [15] where Xray diffraction techniques have been applied. In many of these cases, however, variations in the material constituents/ compositions were neglected as a source of uncertainty.…”