FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 2 6 4 Note: This is an excerpt from the HTS Prime Industry Contributor award winning article, Retained Austenite Benefits or Avoidance Requires Dependable Determination, which can be accessed here https://doi.org/10.31399/asm. cp.ht2021p0212. ~HTPro For more information: Thomas Wingens, Wingens LLC, Sewickley, PA, 724.732.3338, thomas@wingens.com, wingens.com. References 1. J.D. Verhoeven, Steel Metallurgy for the NonMetallurgist, ASM International, 2007. 2. W. Beck, Werkstoffkunde Stahl für Studium und Praxis, s.l., Institut für Eisenhüttenkunde, RWTH Aachen, 2010. 3. H. Kitagawa and T. Sohmura, An X-ray Diffraction Method for Quantitive Determination of Retained Austenite in the Production Line of Metastable Austenitic Steel, Kyoto, JP : ISIJ, 1983. 4. H.K.D.H. Bhadeshia, Steel for Bearings, Prog. Mater. Sci., Vol 57, p 268-435, 2012. 5. W. Pitsch and G. Sauthoff, Typische Stahlgefüge. s.l., Springer Verlag, 1984. 6. N. Herres and R. Schneider, Herausforderungen und Messunsicherheiten bei der Bestimmung des Restaustingehaltes, Buchs, CH: s.n., 2015. 7. A. Creuziger and T. Gnäupel-Herold, Uncertainty in Retained Austenite Measurements Applied to Individual Crystallographic Orientations. s.l., 17th International Conference on Texture of Materials, 2015. 8. T. Wingens, Development of a Retained Austenite Corporate Standard, Gothenburg, Sweden, AB VOLVO, 1995. are typicallynot valid for rolled sheet steel (suchas transformation induced plasticity “TRIP” steels). There is data to indicate that the transformation will not be distributed evenly as a function of orientation, but particular stress states will cause some orientations to transform at a higher rate than other orientations. A technique using complete pole figure averaging using neutron diffraction was developed to measure the retained austenite in textured TRIP steels as well as provide an estimate on the uncertainty in the phase fraction[7]. CONCLUSIONS Retained austenite plays a significant role in the performance of heat-treated steel components. Data indicates even very small amounts of RAmay be influential. The ideal RA depends on the alloy and its application. As a result, appropriate measurement techniques and process controls need to be implemented to deliver targeted performance. Light microscopy provides qualitative assertion with a subjective quantitative assumption, however, retained austenite contents below 15% are hard to determine. Magnet inductive measurement is a volume measurement and needs to be calibrated to specific materials, heat treat, and geometries. The obtained results are usually higher than with XRD, which has no ability to do profile measurements. Results from EBSD measurement are somewhat similar to XRD with much higher requirements for preparation, operator, and equipment. XRD measurement is unproblematic with untextured (isotropic) homogeneous steels. The presence of additional phases and reflections due to grain size, carbides, or texture can cause disturbances and variances. However, the newest generation XRD machines can compensate for these obstacles and provide precise, repeatable, and fast measurements at a very competitive cost. Acknowledgments The author would like to thank the companies Vericheck LLC, Bethel Park, Pa., and GNR Analytical instruments, Italy, for the support of this work. 14
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