Reverse transformation of deformation-induced martensite in austenitic stainless steel studied by positron annihilation

Abstract

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.

Positron annihilation studies of high-manganese steel deformed by rolling

“…After this stage, the S parameter values for the samples studied do not differ significantly. A similar behavior was observed for deformed 1.4301 SS and 1.4307 SS [12,16,17], but in that case, the decrease starts at higher temperature of about 200C and continues up to 450C, open triangles in Fig. 3.…”

“…The defect generation is less pronounced than during the -martensite reversion in stage II. The temperature range of stage III coincides with the increase in the S parameter for the deformed 1.4301 SS, which was ascribed to the generation of defects during -martensite reversion [12]. Volume contraction accompanying bcc or fcc change during -martensite reverse transformation results in volume excess that may contribute to the vacancy cluster formation.…”

“…In our previous publication, we reported the positron annihilation studies of annealing behavior of deformed austenitic stainless steel (SS) 1.4301 (EN) [12]. The annealing of defects induced by plastic deformation and generation of other defects by reverse transformation of deformation-induced martensite (DIM) was observed.…”

High temperature thermal stability of nanocrystalline 316L stainless steel processed by high-pressure torsion

“…The unchanged dislocation density is most probably caused by a balance between the annihilation of dislocations due to annealing and their formation owing to the stresses induced by the phase transformation. Earlier studies [32] showed that the phase transformation of α′-martensite to γ-austenite is accompanied by a volume contraction which may yield internal stresses and the formation of lattice defects. Indeed, it was revealed that vacancy clusters consisting of ~6-9 vacancies formed at the interface between α′-martensite and γ-austenite after the reverse phase transformation [32].…”

Temperature dependent measurement of internal damping of austenitic stainless steels

“…The deformation-induced martensite transformation into austenite is accompanied by migration and reduction of vacancies an creation of additional lattice imperfections [8]. The reverse process is then accompanied by the formation of annealing twins where the accumulated excessive energy is reduced [9].…”