Investigating on the Reverse Transformation of Martensite to Austenite and Pseudoelastic Behavior in Ultrafine-Grained Fe-10Ni-7Mn (wt %) Steel Processed by Heavy Cold Rolling

Abstract

Fe-10Ni-7Mn (wt. %) steel is a member of ultrahigh strength steels which shows good ductility in the solution annealed condition and excellent age hardenability. In the current research, this alloy was subjected to heavy cold rolling in which the reverse transformation of martensitic to austenite was brought about. From the XRD, DSC and dilatometric analyses, it is resulted that after 60 % cold rolling the austenite phase may be formed by displacive mechanism. Stability of austenite at room temperature is referred to the ultrafine/nanograin size of austenite after deformation which prevents the austenite to martensite transformation. The presence of ultrafine/nanoaustenite formed by displacive mechanism leads to the observation of new mechanical properties during cyclic tensile test. This behavior is known as pseudoelastic phenomenon. In this behavior, during loading-unloading tensile cycle, the shape of the specimen return to its original configuration with a hysteresis loop in its path to the zero strain point.

Reversible Phase Transformation in Polycrystalline TRIP Steels Induced by Cyclic Indentation Performed at the Nanometric Length Scale

“…Within this context, the phase transformation under loading is the most widely reported reason for occurrence of pseudoelasticity in Fe‐based shape memory alloys, where the pseudoelasticiy phenomenon is mainly observed during the cyclic loading process as reported in refs. .…”

On the microstructure and mechanical properties of an Fe-10Ni-7Mn martensitic steel processed by high-pressure torsion

“…Based on the EBSD phase maps it is apparent that the HPT processing induces a small fraction of austenite phase in the initial martensitic microstructure. Earlier reports demonstrated the possibility of a reverse transformation of martensite to austenite in SPD processing [8,13,26] where the reverse transformation occurs if the applied stress on the material supplies sufficient driving force in terms of chemical and non-chemical elements. The chemical driving force originates from the difference in the Gibbs free energies in the original and the new phases while the non-chemical driving force corresponds to the energy required for nucleation and growth of the new phase [8].…”

“…To date, several SPD processing methods have been applied to Fe-10Ni-7Mn steel such as equal-channel angular pressing (ECAP) [12], severe cold rolling [13,14] and repetitive corrugation and straightening by rolling (RCSR) [15]. The results reveal that by 85% severe cold rolling the ultimate tensile strength increases to ~950 MPa but the elongation to failure decreases to ~14% [12].…”

“…According to these earlier studies, grain refinement by SPD methods in Fe-10Ni-7Mn martensitic steel is frequently accompanied by a phase transformation of martensite to austenite due to a deformation-induced reverse transformation [8]. It was demonstrated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) that 60% of cold rolling supplied the driving force required for the reverse transformation of martensite to austenite [13]. It is noteworthy to mention that austenite stability at room temperature is also related to the grain size after SPD processing which may hinder the austenite to martensite transformation.…”

Effect of high-pressure torsion on the microstructural evolution and mechanical properties of an Fe-10Ni-7Mn (wt. %) lath martensitic steel

“…Discontinuous coarsening of grain boundary precipitates resulting in the formation of precipitate-free zones along prior austenitic grain boundaries was found as the main source of embrittlement in aged Fe-10Ni-7Mn steels [9]. The ductility improvement in this alloy has been the subject of many reports [15,16]. Grain refining has been known as an effective way to improve the strength and toughness of metallic materials [9].…”