Correlative cross-sectional characterization of nitrided, carburized and shot-peened steels: synchrotron micro-X-ray diffraction analysis of stress, microstructure and phase gradients

Mechanical properties of case modified steels depend decisively on the near-surface gradientsof residual stresses, microstructures, phases and chemical composition, which aregenerated by the empirically well-established case-hardening techniques. Currently,however, to obtain the correlation between near-surface structureeproperty gradients,applied hardening process parameters and steels’ overall performance is a very challengingtask. In this work, high-energy synchrotron cross-sectional X-ray diffraction(CSmicroXRD) using a pencil beam cross-section of 20 500 mm2 and complementaryanalytical techniques are used to characterize the surface-to-bulk gradient of (i) a plasmanitrided steel W300, (ii) a carburized case hardening steel (grade 18CrNiMo7-6) and (iii) ashot-peened high strength steel, type 300M. CSmicroXRD analysis reveals complex gradientsof martensite and austenite phases, residual stresses in both phases, crystallographictexture and the evolution of diffraction peak broadening with a spatial resolution of~20 mm. These parameters are correlated with the gradients of hardness, morphologymicrostructureand with the changes in N and C concentrations and/or retainedaustenite formation/depletion in all three model samples. Finally, the correlative microanalyticsapproach indicates the complexity of near surface structure-property relationshipsas well as the importance of innovative cross-sectional characterization, whichallows for assessing gradual near-surface physical and/or chemical changes accompanyingthermo-chemical and mechanical surface treatment

Micro-fabrication of ceramics : additive manufacturing and conventional technologies

Peer reviewedPublisher PD