ROLLING-CONTACT FATIGUE OF 3 PEARLITIC RAIL STEELS

The effects of varying contact pressure and creepage on the early stag es of rolling contact fatigue in three pearlitic rail steels have been investigated in the laboratory under water lubricated conditions. Tn the test machine used, a non-contacting eddy current probe detected ve ry small fatigue cracks and was used to stop tests before spalling cou ld destroy the fatigue initiation sites in order that the metallograph y of crack initiation could be undertaken. Crack morphologies similar to those found in wheel-rail contact have been observed. Except at the highest creepages and contact stress used, there was little evidence that manganese sulphide inclusions contributed to crack initiation. In contrast, hard oxide inclusions did contribute to initiation. The hea d-hardened grade eutectoid steel had the best resistance to rolling co ntact fatigue, The naturally hard eutectoid steel was the next best, w hilst the lowest strength steel gave the worst performance. Crack netw orks were formed in the specimens tested at nominal contact stresses o f 1200 MPa and 1500 MPa. Isolated cracks were produced in the specimen s tested at 1800 MPa.