During a wheel-rail slide, the temperature is high enough to austenitize the material close to the contact surface. The material is rapidely cooled by heat conduction into the rest of the wheel when the wheelset starts rolling again and thus martensite can form in the surface layer. The TAZ (mechanically and thermally affected zones) under railway wheel flats have been studied by optical microscopy, scanning microscopy and hardness testing. The wheel flat samples were generated in full-scale experiments on the last axle of a train consisting of a locomotive pulling three carriages. The axle load, train speed and locking time of the last axle were varied to simulate several different situations that arise in revenue traffic. The entire population of samples has earlier been studied, but the present investigation goes more into detail on a limited number of samples. Several discoveries are made and suggestions of mechanisms are presented. Among the most important findings are stretched MoS inclusions that act as crack nucleation sites, limited grain growth indicating low austenitization temperatures and reformation of ferrite and pearlite in the deformed surface layers.
Microstructural evaluation and interpretation of the mechanically and thermally affected zone under railway wheel flats
1999
14 Seiten, 9 Bilder, 3 Tabellen, 30 Quellen
Aufsatz (Zeitschrift)
Englisch
Eisenbahnrad , Eisenbahnschiene , Gleitkontakt , Reibung , Wärmeentwicklung , Austenitisierung , Wärmebelastung , Rissbildung , Einschluss , Phasenumwandlung , Martensit , Oberflächenverformung , optische Mikroskopie , REM (Rasterelektronenmikroskopie) , Mikrostruktur , Abplatzen , Stahl (nach Anwendung) , Härte
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