Deformation Bands in High‐Alloy Austenitic 16Cr6Mn6Ni TRIP Steel: Phase Transformation and Its Consequences on Strain Hardening at Room Temperature

Abstract

In this study, the formation of deformation bands during plastic deformation in austenite is analysed. The movement of (partial) dislocations on neighboring lattice planes formed pronounced deformation bands, which were identified as ϵ‐martensite if the stacking faults are predominantly aligned on every second {111} lattice plane. In these deformation bands, α′‐martensite nuclei are formed, severely fragmenting the mean free path of dislocations. The strain hardening is found to depend directly on the nucleation rate of α′‐martensite. The α′‐martensite nuclei represented effective barriers for (partial) dislocation movement in the deformation bands. On the basis of three different grain sizes, the strain‐hardening capability of the martensitic γ → ϵ → α′ phase transformation is analysed. Although the triggering stress for nucleation of α′‐martensite is influenced by grain size, the absolute value of the strain hardening due to α′‐martensite formation is the same. This is related to the fact that the continuous fragmentation of the dislocation mean free path is in the same order of magnitude for all grain sizes. Using a basic approach that treated the continuous reduction of the dislocation mean free path as a Hall–Petch‐like effect, comparable with strain hardening in TWIP steels, the contribution of the effect to the increasing strength in austenitic TRIP steels is estimated.