Martensitic transformation during deformation of Fe−Ni alloys

Conclusions

• 1. The range of M_s-M_d is considerably narrower for athermal than for isothermal alloys. In connection with this, deformation at a temperature equidistant from M_s may lead to formation of much smaller quantities of martensite in athermal alloys.

• 2. In athermal alloys (N30, N31) the structure of the strain martensite varies with the deformation temperature. Near M_s the strain martensite is similar to martensite formed during cooling. With increasing temperatures the martensite formed is of another morphological type, similar to isothermal martensite.

• 3. In alloys N28, N29, N30, and N31 with phase strain hardened austenite the formation of martensite is accelerated considerably at small deformations (1–5%). At the same time, M_d and the completeness of the transformation change negligibly.

• 4. After phase strain hardening of athermal alloys the anomalous drop of the proof stress near M_s is retained. Phase strain hardening induces this effect in isothermal alloy N28.

• 5. In the process of deformation at temperatures ensuring the optimal rate of martensite formation (40–50% martensite up until fracture) the ductility of both quenched and phase strain hardened austenite increases considerably.