Evaluation of local strength via microstructural quantification in a pearlitic rail steel deformed by simultaneous compression and torsion

Abstract

Pearlitic steels are commonly used for railway rails because they combine good strength and wear properties. During service, the passage of trains results in large accumulation of shear strains in the surface layer of the rail, sometimes leading to crack initiation. Knowledge of the material properties versus the shear strain in this layer is therefore important for fatigue life predictions. In this study, fully pearlitic R260 rail steel was deformed using a bi-axial torsion-compression machine to reach different shear strains. Microstructural parameters including interlamellar spacing, thickness of ferrite and cementite lamellae and dislocation density in the ferrite lamellae, as well as hardness were quantitatively characterized at different shear strain levels. Based on the microstructural observations and the quantification of the microstructural parameters, the local flow stresses were estimated based on boundary strengthening and dislocation strengthening models. A good agreement was found between the estimated flow stresses and the flow stresses determined from microhardness measurements.

Local stress and strain in heterogeneously deformed aluminum: A comparison analysis by microhardness, electron microscopy and finite element modelling

“…The finer the deformation structure, the smaller the chosen step size. TEM foils are made via a double-jet electro polishing technique applied in recent studies (Zhang et al, 2012b;Chen et al, 2015;Zhu et al, 2017;Nikas et al, 2018). The TEM foils are investigated using a JEOL 2000FX TEM at 200 kV.…”

Deformation and Microstructural Evolution of Nanostructured Pearlite under Tension versus Torsion

“…Recent studies have recorded a rapid decrease in the pearlitic lamellae spacing beyond a shear strain of 1.2 for pearlitic rail steel specimens subjected to combined compression and torsion. [ 6 ] Moreover, the increase in shear strain is accompanied by an increase in the dislocation density which subsequently increases the local hardness. [ 6,22 ] However, in the current study, the specimens fractured at a maximum shear strain of 0.51 and therefore no appreciable refinement of lamellar structure is observed.…”

“…[ 6 ] Moreover, the increase in shear strain is accompanied by an increase in the dislocation density which subsequently increases the local hardness. [ 6,22 ] However, in the current study, the specimens fractured at a maximum shear strain of 0.51 and therefore no appreciable refinement of lamellar structure is observed. Zhou et al [ 20 ] have examined the torsional behavior of cold‐drawn pearlitic steel wires and linked the torsional response to the crystallinity and morphology of the cementite phase.…”

“…Therefore, a lot of experimental studies combining axial and torsional loading have been done to simulate the plastic flow of pearlitic rail steel under service. [ 3–6 ]…”

Interactions between Dislocations and Boundaries during Deformation

“…Dislocations-phase interface interactions play an important role for structural metals, in not only the strength [ 136 , 137 ], but also other mechanical properties such as ductility and toughness [ 138 ], wear resistance [ 139 ], fatigue properties [ 140 , 141 , 142 , 143 ] and micro-pitting [ 144 ], as well as the properties of heterogeneous structures [ 145 , 146 , 147 ]. All these need the systematic investigations with exquisitely designed experiments and/or simulations.…”