Neutron Diffraction Study of Plasticity-Induced Martensite Formation of the Austenitic Stainless Steel AISI 321

The elastic and plastic properties of the austenitic matrix and martensitic areas induced during cyclic tensile-compressive loading of low carbon metastable austenitic stainless steel were studied in an in-situ stress rig experiment on the ENGIN instrument at the ISIS pulsed neutron facility. Two sets of samples were prepared from the steel AISI 321. The first set of samples (annealed at 1050 degreesC and quenched in water) was cycled under strain control with a strain amplitude of 1% at a frequency of 0.5 Hz. The second set (1070 degreesC / quenched in air) was cycled under stress control with a stress amplitude of 330 MPa at 5 Hz. The applied stress - elastic strain responses of the austenitic and martensitic phases were obtained by Rietveld and Le Bail refinements of the neutron diffraction spectra. The results of the modified refinements accounting for the elastic anisotropy in polycrystalline materials under load are also presented. The residual strains were determined for the first set of samples using a noncycled sample as a reference sample.