The reversion of deformation-induced a 0 -martensite in tension-deformed 1.4301 (EN) stainless steel was investigated using positron annihilation spectroscopy. The Doppler broadening of the annihilation line and positron lifetime spectroscopy were applied to study defect structure and its annealing behavior in samples with a similar deformation level but varying in a 0 -martensite amount. The difference in a 0 -martensite was obtained by applying different deformation temperatures, i.e., liquid nitrogen temperature, room temperature, and 200°C. The cumulative annealing of the tension-deformed samples and measurement of the positron annihilation characteristics show the gradual annealing of defects in the temperature range between 200 and 400°C due to the recovery and recrystallization. However, in the temperature range between 450 and 650°C, the generation of vacancy clusters which trap positrons is revealed. This temperature range coincides with the temperature range of a 0 -martensite reversion which is confirmed by microhardness and magnetization measurements. The detected large vacancy clusters consisting of 6-9 vacancies can occur at the interface between austenite and a 0 -martensite phases due to the volume contraction accompanying bcc/fcc change.

Abstract. Positron annihilation spectroscopy (PAS) has been used to study the annealing behavior of cold rolled Fe -21 wt% Mn steel with 0.05 wt% C. After the initial annealing of defects shown by Doppler broadening of the annihilation line, a slight increase in the annihilation line shape parameter, i.e., the so-called S parameter and then its decrease in the temperature range between 225C and 450C indicates generation of new defects and their subsequent annealing. This temperature range coincides with X-ray diffraction measurements, which indicate reversion of deformation-induced -martensite. However, for annealing in this temperature range with slow cooling of the sample, the formation of ferrite already starts. The results are compared with our previous results for deformed austenitic stainless steel 1.4301 (EN) where only reversion of deformation-induced -martensite was detected.

Cumulative isochronal annealing of stainless steel 1.4307 samples deformed by compression was investigated using the Doppler broadening of the annihilation line measurements. Higher level of plastic deformation is accompanied not only by higher concentration of defects but also by higher amount of α martensite. The annealing studies revealed creation of defects in the temperature range between 450• C and 650• C pointing out the reverse transition of α martensite to austenite. This is conrmed by magnetic susceptibility and microhardness measurements.

The paper presents the results of research of nanocrystalline AISI 316L type stainless steel and nanocrystalline Armco pure iron processed by severe plastic deformation using hydrostatic extrusion method. Surface and subsurface of the steel samples extruded at different pressure were investigated using variable energy positron beam. It enabled us to determine the positron diffusion length and compare its values with those for annealed AISI 304 stainless steel. Furthermore positron lifetime and microhardness were measured for all the samples and X-ray diffraction was used to estimate the crystallite size.

W artykule przedstawiono badanie obserwacji zmian udziału defektów sieci krystalicznej w austenitycznej stali nierdzewnej. Próbki zostały poddane naciskowi mechanicznemu o wartości od 12 MPa do 120 MPa, co dało odkształcenie w przedziale od 2% do 16% grubości. Badania były prowadzone procesem izochronicznym w zakresie temperatur od 25°C do 725°C. Pomiar wykonany został metodą anihilacji pozytonów uzyskanych w wyniku rozpadu izotopu germanu. Linia anihilacyjna od par e + ezostała uzyskana za pomocą detektora germanowego o wysokiej czystości, w wyniku czego wyznaczono parametr S oraz parametr W r , które odzwierciedlają w pewnym stopniu zmiany zachodzące w strukturze krystalograficznej. Na podstawie otrzymanych wyników wyznaczono temperatury, w których następuje przebudowa struktury krystalicznej.