Crystallographic characterization of steel microstructure using neutron diffraction.

ABSTRACT: Applications of neutron diffraction to microstructure evaluation of steel investigated by a project commissioned by the Innovative Structural Materials Association are summarized. The volume fraction of austenite (?) for a 1.5Mn-1.5Si-0.2C steel was measured by various techniques including backscatter electron diffraction (EBSD) and X-ray diffraction. It is recommended to measure volume fraction and texture simultaneously using neutron diffraction. The ? reverse transformation was in situ monitored using dilatometry, EBSD, X-ray diffraction and neutron diffraction. The ? reversion kinetics showed excellent agreements between dilatometry and neutron diffraction, whereas the ? formation started at higher temperatures in EBSD and X-ray diffraction measurements. Such discrepancy is attributed to the change in chemical compositions at the specimen surface by heating; Mn and C concentrations were decreased with heating. Phase transformations from ? upon cooling were monitored, which enabled us to elucidate the changes in lattice parameters of ferrite (?) and ? affected by not only thermal contraction but also transformation strains, thermal misfit strains and carbon enrichment in ? in the above hypoeutectoid steel. Pearlitic transformation started after the carbon enrichment reached approximately 0.76 mass% and contributed to diffraction line broadening. Martensitic transformation with or without ausforming at 700°C was monitored for a medium carbon low alloyed steel. Dislocation density after ausforming was determined using the convolutional multiple whole profile fitting method for 10 s time-sliced data. The changes in ? and martensite lattice parameters upon quenching were tracked and new insights on internal stresses and the axial ratio of martensite were obtained.

SUBMITTER: Tomota Y 

PROVIDER: S-EPMC7008240 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature