Influence of thermal loading on mechanical properties of railway wheel steels
Doktorsavhandling, 2012

Material integrity and properties of wheels are critical in railway traffic, as wheels fulfil the important function of transferring load and traction from the vehicle to the rail track. Steels with a pearlitic microstructure are commonly used for wheels due to their height strength, low cost and good wear properties. However, the pearlitic microstructure and behaviour can be altered by thermal and mechanical load being present in the contact between wheel and rail. As very high power is available, a few milliseconds of time where the slip between wheel and rail becomes large can cause small material volumes in the contact to be heated several hundred degrees Celsius. The present work was initiated with the main purpose to investigate the effects of rapid thermal heating and cooling on wheel material. Cyclic and monotonic mechanical testing was performed to study the effects of thermal softening on virgin wheel material and on used wheels taken out from service. Furthermore, material in both pearlitic and martensitic state was investigated during rapid heating and cooling cycles by methods as laser and resistive heating for different loading conditions. It was shown that alloying composition of different wheel steels could decrease sensitivity to thermal loads, while plastic deformation had the opposite effect when the material was subjected to long time thermal loading. For the typically very short heating times present in the wheel rail interface no significant permanent effects on mechanical properties were measured for pearlitic material. However, for martensitic material, substantial permanent hardness decrease progressed within fractions of a second at elevated temperature. This rapid tempering behaviour was observed to progress even faster in the presence of an external load. Moreover, the inherent different behaviours of pearlite and martensite can result in different residual stress fields for the case of local heating on the tread surface, affected by heating rate, peak temperature and duration. Some additional effects of frictional heating and the influence of wear debris within cracks for rolling contact fatigue cracks were also investigated by use of image and chemical analysis.

contact creep.

rolling contact fatigue

martensite tempering

shear deformation

Railway wheel steels

heat treatment

residual stress

rapid heating

low cycle fatigue

Virtual Development Labratory, Hörsalsvägen 7a, Chalmers
Opponent: Professor Dietmar Eifler, Technische Universität Kaiserslautern, Germany

Författare

Krste Cvetkovski

Chalmers, Material- och tillverkningsteknik, Materialteknologi

The material and structural properties of wheels are of great importance in railway traffic, since they are the only path to transfer loads and traction from the vehicle to the rail track. Historically medium to high carbon steels have been used, over time developed to accommodate the heavy haul traffic and faster running passenger trains. With an expanding European market and large investment in the railway sector, train manufacturers and operators are aiming for increased train speeds and loads with retained safety and wheel maintenance costs. Thermal damage on wheels and rail is problematic, as it can lead to crack initiation, increased wear rates and deterioration of profiles. As very high power is available, for even a few milliseconds of time where the slip between wheel and rail becomes large, small material volumes in the contact can be heated several hundred degrees. The present work was initiated with the main purpose to investigate the effects of rapid thermal heating and cooling on wheel material.

Ämneskategorier

Materialteknik

Metallurgi och metalliska material

Styrkeområden

Materialvetenskap

ISBN

978-91-7385-750-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie

Virtual Development Labratory, Hörsalsvägen 7a, Chalmers

Opponent: Professor Dietmar Eifler, Technische Universität Kaiserslautern, Germany