Study of mechanical features for low cycle fatigue samples of metastable austenitic steel AISI 321 by neutron stress analysis under applied load

The elastoplastic properties of the austenitic matrix and martensitic volume areas induced during cyclic tensile-compressive loading of low carbon metastable austenitic stainless steel were studied in an in situ neutron diffraction stress rig experiment on the ENGIN instrument at the ISIS pulsed neutron facility. Samples prepared from the steel AISI 321 annealed at 1050°C and quenched in water were subjected to low-cycle fatigue under total-strain control with an amplitude of 1% at a frequency of 0,5 Hz. Subsequent applied stress-elastic strain responses of the austenitic and martensitic phases were obtained by Rietveld and Le Bail refinements of the neutron diffraction spectra, and were used to determine the elastic constants of the phases as a function of fatigue level. The results of modified refinements accounting for the elastic anisotropy in polycrystalline materials under load are also presented. The residual strains in the austenitic matrix were determined as a function of fatigue cycling, using a noncycled sample as a reference sample. The residual macrostresses and the deviatoric components of the phase residual microstresses were determined assuming that the elastic properties of both phases are similar. The Investigation has been performed at the Frank Laboratory of Neutron Physics, JINR.