Author(s)

S. Nishida, N. Hattori & T. Miyake

Abstract

The authors have focused on the \“dark spots”, which are initiated from white phase due to the contact between wheel and rail, especially in the Shinkansen track. Most of these defects have been initiated on the high-speed rail track at more than 150 km/h and in the accelerated train’s section. Though the dominating factors for the dark spot’s initiation have not necessarily been clarified yet, it has been observed that the white phase exists and the contact rolling fatigue cracks are propagated through the white phase. As the white phase consists of 90% martensite and 10% residual austenite, it is very brittle and the contact rolling fatigue cracks are easily initiated due to cyclic loading. Therefore, it is considered that this white phase would be one of the causes for generating the contact rolling cracks in Shinkansen rails. The object of this study is to investigate the mechanism of contact rolling fatigue defects in view of the initiation mechanism of dark spot, which is also known as the shelling defect. The authors considered that the initiation of the contact rolling defects relates to Hertizn stress, lubrication, tangential forces etc. The main results obtained in this study are as follows: (1) The white phase would be generated due to the alternate conditions between water lubrication and dryness. (2) The tangential force affects the contact rolling fatigue crack initiation and propagation properties. (3) White phase has been generated at an early stage according to the observation results of the contact rolling fatigue mechanism. Keywords: contact rolling fatigue, rail steels, white phase, shelling, fatigue crack, lubrication, Hertzian stress. 1 Introduction As far as the surface defects in the running rail head, there are mainly two kinds of defects called the \“head checks” and \“dark spots (or shelling defects)” in the

Keywords

contact rolling fatigue, rail steels, white phase, shelling, fatigue crack, lubrication, Hertzian stress.