Martensite characterization in multiphase steels using neutron diffraction

Previous use of the diffraction technique as a means of characterizing microstructure in multiphase steels has been generally limited to measurements of retained austenite. Other phases, specifically martensite, have not been examined in complex microstructures since there exists peak overlap with ferrite. This research looks at using neutron diffraction as a means to characterize martensite in a multiphase steel microstructure, thus providing a more complete characterization tool.Three low carbon steels, comprised of a dual-phase, ferrite-martensite microstructure, were used in this study. Two diffraction methods were investigated; a direct deconvolution of the martensite peaks from the ferrite peak, and an indirect determination of martensite volume fraction from ferrite peak broadening. Lastly, mechanical properties were investigated in order to determine if a correlation exists with ferrite peak broadening.The results indicate that the martensite phase has a prominent strain broadening effect in diffraction. The nature of this strain effect was hypothesized and a model was developed to confirm the findings. Finally, tensile testing showed that the mechanical properties were dependent on peak broadening and martensite volume fraction