Enhancement in grain-structure and mechanical properties of laser reversion treated metastable austenitic stainless steel

The role of grain size in static and cyclic deformation behaviour of a laser reversion annealed metastable austenitic steel

“…The dissenting results of a relatively homogeneous cross section of the present material in comparison with the other studies using a laser beam 37,38 could be due to different thickness reductions, different α′‐martensite fractions after cold rolling and different beam parameters. However, the most important difference between investigations in previous studies 37,38 seems to be the chemical composition of the studied steel resulting in different reversion mechanism. The reversion behaviour was investigated on steel AISI 301LN, which is known to undergo a diffusional reversion (cf 16,53 …”

“…Thus, neither nonreverted α′‐martensite nor a significantly heterogeneous grain size distribution over the cross section was revealed. This is in contradiction to former reports on the microstructure after heat treatment by the one‐sided application of either an EB 39 or a laser beam 37,38 . The investigations on EB 39 reversion treatment were based on steel with comparable chemical composition and sheet thickness (3 mm) but a lower thickness reduction of 70% and an α′‐martensite fraction of 51 vol.% (cf., 7 same material as 39 ).…”

“…Comparing the different laser heat treatments, the slowest LS with 4.5 mm/s as expected led to the highest peak temperatures (Figure 3A) and vice versa (Figure 3C). As all other beam parameters were kept constant, the heat input is the higher the slower the laser beam speed is along the steel sheet 37 . The laser heat treatments at LS = 4.5 mm/s and LS = 6.0 mm/s exhibit average peak temperatures of 989°C and 779°C, respectively, both with a relatively small standard deviation of about 5°C (see Table S1 for listing of all recorded peak temperatures).…”

“…As all other beam parameters were kept constant, the heat input is the higher the slower the laser beam speed is along the steel sheet. 37 The laser heat treatments at LS = 4.5 mm/s and LS = 6.0 mm/s exhibit average peak temperatures of 989 C and 779 C, respectively, both with a relatively small standard deviation of about 5 C (see Table S1 for listing of all recorded peak temperatures). In contrast, in the case of LS = 7.0 mm/s, an average peak temperature of 608 C was recorded with a high standard deviation of about 44 C. This high scatter for the highest LS probably stems from a more sensitive influence of the exact position of the thermocouple in relation to the oscillation of the laser beam as F I G U R E 3 Signals of the thermocouples attached to the bottom of the steel sheets for the laser heat treatments at the linear speeds the wavelength of the laser's path on the material slightly increases from 2.8 mm for LS = 6.0 mm/s to 3.4 mm for LS = 7.0 mm/s.…”

“…The laser and EB technologies, for example, offer a very local heat input, but on the other hand, the one‐sided application of the heat source impedes a uniform microstructure and grain size over the cross section. Consequently, previous studies 37–39 reported a difference between the top and bottom surface of the steel sheets. However, in case of Heinze et al 39 investigating steel with similar chemical composition as the present work, the grain size gradient over the cross section was reduced using appropriate scan strategies and EB parameters.…”