Effects of Stress on Martensite Transformation During Continuous Cooling and Mechanical Response of a Medium-Carbon High-Strength Steel

Future Trends on Displacive Stress and Strain Induced Transformations in Steels

“…The appearance of the metastable phases named in this section as a product of SIT/DIT mainly depends on the chemical composition of the steel and on the deformation temperature. Hence, whereas the formation of stress or strain induced α is very common in many different microstructures [23,25,35,[49][50][51][52][53][54][55][56], ε is mainly found in austenitic steels [23,25,39,48,52], although it has been sporadically detected in multiphase steels [47]. The formation of α B has not been reported, to the authors' knowledge, at room temperature, although it has been found in fully austenitized steels [35] and in multiphase steels [1,3,57] deformed at high temperatures.…”

“…However, if a stress below σ Y is applied to the structure, the driving force for the transformation increases (in absolute value) and so does the volume fraction of α , reaching even 100% in some cases. It has been previously reported that austenitic structures subjected to stress are able to transform to α in a higher extent than the same structures in a stress-free state [49]. After that, if the load was removed, the volume fraction of austenite would not further go up.…”

“…Usually, the initial structure is fully austenitic, either because the steel of study is austenitic or because it has been previously austenitized (high temperature deformation). In this case, if the cooling rate was high enough to avoid ferritic/pearlitic/bainitic transformations, a martensite transformation would happen [49,92,100]. The transformation would be athermal, it would start at a temperature M s (σ) [49,92,100], where M s (σ) would be higher than M s if the deformation mode was uniaxial tension, uniaxial compression or torsion [49,92,[100][101][102][103].…”

“…In this case, if the cooling rate was high enough to avoid ferritic/pearlitic/bainitic transformations, a martensite transformation would happen [49,92,100]. The transformation would be athermal, it would start at a temperature M s (σ) [49,92,100], where M s (σ) would be higher than M s if the deformation mode was uniaxial tension, uniaxial compression or torsion [49,92,[100][101][102][103]. In addition, in cases in which the M α f temperature was above room temperature, the α volume fraction would increase under stress, because of the additional mechanical driving force and (if the applied stress was above the austenite σ Y ) the increase in nucleation sites [49].…”

“…The transformation would be athermal, it would start at a temperature M s (σ) [49,92,100], where M s (σ) would be higher than M s if the deformation mode was uniaxial tension, uniaxial compression or torsion [49,92,[100][101][102][103]. In addition, in cases in which the M α f temperature was above room temperature, the α volume fraction would increase under stress, because of the additional mechanical driving force and (if the applied stress was above the austenite σ Y ) the increase in nucleation sites [49]. In cases in which no plastic deformation was introduced, the addition of the mechanical driving force would not only affect the start of the α transformation, but also the selection of specific crystallographic variants [84,[104][105][106], especially during the first stages of the transformation [106].…”