Thermal degradation of pearlitic steels: Influence on mechanical properties including fatigue behaviour

Abstract

With the aim to predict the durability of railway wheels, thermomechanical damage was studied for two steels with different alloying levels of silicon and manganese in the temperature range of 500–725°C. Softening caused by cementite spheroidisation in pearlite leads to changes in the mechanical behaviour and an accompanying decrease in fatigue lifetimes. It was found that higher contents of Si and Mn lead to better resistance to softening of both virgin and plastically deformed material. Correspondingly, the high Si-Mn alloyed steel loses much less in fatigue lifetime than the lower alloyed steel.

Differences in service-exposed and artificially aged microstructure and tensile properties of ASTM A204 Grade C steel

“…As a result of pearlite degeneration taking place during ageing, the pearlite phase becomes softer [15,24] which leads to the decrease in UTS of the 675C-24hr aged sample. At the same time, segregation of alloying elements from ferrite matrix would mean lower solid solution strengthening contribution from matrix, leading to lower UTS and better ductility.…”

Influence of short heat pulses on properties of martensite in medium carbon steels

“…Above ca. 400 1C a slight deviation is visible, which may be related to spheroidisation of pearlite [7]. Similar thermal expansion during heating for pearlite and tempered martensite would be expected since the phase constituents are similar and morphology effects are small.…”

“…Such local heating often has a short duration and is normally followed by self-cooling with large cooling rates. If the heating pulses cause peak temperatures above some 400-600 1C, softening of the pearlitic microstructure takes place resulting in easier plastic deformation and distortion under loading [7]. Even more important are heating cycles extending over the austenitisation temperature (T A1 ) which may lead to martensite formation during rapid cooling.…”

The role of microstructure and its stability in performance of wheels in heavy haul service

“…The kinetics of spheroidisation are influenced by temperatures, accumulated exposure times, the extent of work hardening and alloying compositions. It is worth noting that severe plastic deformation at the wheel surface enhances spheroidisation by causing thinning and break-up of the lamellar carbide structure [4][5][6][7][8]. Simultaneously, spheroidisation allows more plastic deformation under the same level of wheel-rail loading.…”

“…The high-level plastic deformation on the wheel surface due to the combined effects of high contact stress and creepage conditions can accelerate this spheroidisation process by fracture and partial dissolution of cementite lamella in the pearlitic structure; this process is further enhanced by the increased dislocation density in the ferrite and ferrite/cementite interfaces during near-surface deformation due to accelerated carbon diffusion at dislocations [4][5][6][7][8].…”