Krste Cvetkovski

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

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.

Rapid thermomechanical tempering of iron–carbon martensite

Abstract Tempering of martensite under simultaneous compressive stress has been studied within the temperature range of 20–400°C. Resistive heating was utilised to obtain rapid heating and cooling cycles of a few seconds. Material was obtained from a medium carbon pearlitic railway wheel steel, quench hardened to obtain martensitic structure. Greater than ∼150°C dilatation effects where observed below the global yielding point of the material. Microstraining around dislocations in the body centred tetragonal crystallographic structure or viscous flow at higher temperatures was a probable explanation to this material behaviour. Hence, external stress may have an important influence on the tempering progression of martensitic steel. The trials also showed that tempering of martensite progresses fast, is near instantaneous and is independent of the presence of external stress or not.