The reason why thermal cycling decreases the martensite start (Ms) temperature of an Fe-17 wt pct Mn alloy was quantitatively investigated, based on the nucleation model of ε martensite and a thermodynamic model for a martensitie transformation. The Ms temperature decreased by about 22 K after nine cycles between 303 and 573 K, due to the increase in shear-strata energy (ΔGsh) required to advance the transformation dislocations through dislocation forests formed in austenite during thermal cycling. The ΔGsh value increased from 19.3 to 28.8 MJ/m3 due to the increase in austenite dislocation density from 1.5 × 1012 to 3.8 × 1013/m2 with the number of thermal cycles (in this case, up to nine cycles). The austenite dislocation density increased rapidly for up to five thermal cycles and then increased gradually with further thermal cycles, showing a good agreement with the increase in austenite hardness with the number of thermal cycles.
|Number of pages||5|
|Journal||Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science|
|Publication status||Published - 2002 Jul|
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Mechanics of Materials
- Metals and Alloys