Thermal and athermal contributions to the flow stress of martensite

Abstract

Recent theories consider as-quenched martensite as a composite which strain hardens by the gradual yielding of constituents. An underlying hypothesis is that hardening comes primarily from athermal hardening contributions. In this contribution, we conducted strain-rate jump and tension-compression tests to quantify the athermal and kinematic hardening contributions in martensite. It is shown that athermal hardening accounts for ~75% of the total strength of as-quenched martensite. The magnitudes of athermal and kinematic hardening decrease as a function of tempering. A correlation between the athermal and kinematic hardening contributions is identified and shown to be independent of chemistry and tempering condition.

Dislocation densities in a low-carbon steel during martensite transformation determined by in situ high energy X-Ray diffraction

“…based on an inverse analysis from the macroscopic mechanical behavior. It was shown that microstructural heterogeneities (dislocation densities, lath sizes, carbon segregations) as well as internal stresses resulting from the transformation deformation must be taken into account to explain the unique behavior of these steels [50]. The density of dislocations appears to be a major contribution explaining almost one half of the stress distribution.…”

“…in the martensite is originated by the microstructure principally (laths sizes, dislocations densities); internal stresses contribute to the phenomenon without being the only explanation as reported by Wang et al [50]. The functional form for the local yield stress spectrum in the CCA model (an Avrami type law [2]) can be selected differently based on the type of distribution found experimentally.…”

Temperature Effects on Tensile Deformation Behavior of a Medium Manganese TRIP Steel and a Quenched and Partitioned Steel

“…Long-range dislocation interactions contribute to the athermal component of flow stress, while the thermal component of flow stress arises from short-range dislocation obstacles, such as the Peierls-Nabarro stress and dislocation forests [7,33]. Wang et al recently quantified the athermal and thermal components of flow stress in quenched and tempered steels [65]. For a steel similar in chemical composition (0.25C-2.42Mn-1.44Si-0.01Al mass%) to the current work that was quenched and then tempered at 400 • C for 5 min, the athermal component accounted for approximately 75% of flow stress [65].…”

“…Wang et al recently quantified the athermal and thermal components of flow stress in quenched and tempered steels [65]. For a steel similar in chemical composition (0.25C-2.42Mn-1.44Si-0.01Al mass%) to the current work that was quenched and then tempered at 400 • C for 5 min, the athermal component accounted for approximately 75% of flow stress [65]. For QP3Mn, temperature-sensitive short-range dislocation barriers do not appear to have a significant impact on flow stress for two reasons: (1) their contribution to flow stress is very small compared with long-range barriers, and (2) the test temperature range is small (i.e., approximately 95 • C), which amounts to a small increase in the thermally dependent component of flow stress.…”

Transitions in the strain hardening behaviour of tempered martensite

“…≤400 °C ) but Al is more effective at high tempering temperature and longer tempering times [35]. However, Bauschinger test results from Wang et al showed that kinematic hardening accounts for a large proportion of the flow stress in tempered martensite and Si is more effective than Al in resisting the reduction in kinematic hardening for all tempering conditions between 300 °C and 600 °C [37].…”