Inheritance of Dislocations and Crystallographic Texture during Martensitic Reversion into Austenite

Abstract

KEY WORDS: austenite; martensitic reversion; reversible martensitic transformations; crystallographic memory effect.

Grain boundary segregation engineering and austenite reversion turn embrittlement into toughness: Example of a 9 wt.% medium Mn steel

“…9. Austenite islands preferentially nucleate at triple junctions, intersections of lath and high-angle grain boundaries, and at PAGBs, as has been observed for Fe-Mn [37,38] and Fe-C [39][40][41]. Table 2 displays absolute grain boundary concentrations and excess values of Mn, C, B and P for different tempering states for both the model alloys Mn9 and Mn9+B.…”

Transition from Diffusive to Displacive Austenite Reversion in Low-Alloy Steel

“…It is known that the reversible transformation from martensite to austenite (martensitic reversion) occurs in maraging steel owing to its high Ni content. [1][2][3][4] Previously, 5) the authors of the current study directly observed an austenitic structure formed by martensitic reversion (martensitically reversed austenite) in 18%Ni-C (% = wt.%) steel. It was reported that after reheating the sample to a temperature above the martensitic austenite-start temperature, As, all martensite laths originally formed via an fcc→bcc martensitic transformation reverse into new austenite during the bcc→fcc martensitic reversion, thus returning to an original austenitic structure with the same crystallographic orientation.…”

“…4(a-2)-4(d-2)) indicate that the lath martensitic structure is characterized by high angle block and packet boundaries and that there is no significant difference in the density of these boundaries among specimens. To reveal the occurrence of the displacive reversion, we must focus not on block and packet boundaries but on the prior austenite grain boundaries; this is because while the original austenite grain boundaries remained in displacive reversion, 3,5) new austenite grains were formed through nucleation and growth in diffusive reversion. In other words, the austenite grain size does not change during displacive transformations.…”

“…It is known that martensitically reversed austenite is easy to recrystallize at elevated temperatures owing to a high dislocation density. [1][2][3][4][5]15) Therefore, it is thought that displacive reversed austenite statically recrystallizes in a short time resulting in the formation of fine austenite grains. These experimental results demonstrate that displacive reversion accompanied by carbon diffusion takes place even in low-alloyed steels when the heating rate is sufficient for suppressing diffusive reversion and also that the displacive-reversed austenite can easily recrystallize.…”

Multiple mechanisms of lath martensite plasticity

“…Another group of interfaces in the lath martensitic microstructure are prior austenite grain boundaries [11,49]. In contrast to packet, block and sub-block boundaries, the character of prior austenite grain boundaries is not determined by the austenitemartensite orientation relationship.…”