Researches on the Improvement of Fatigue Strength by Surface Rolling (1st Report)

This investigation was carried out to clarify the most suitable conditions of surface rolling for the purpose of increasing the fatigue limit. The materials used were four kinds of carbon steels having 0.2∼0.6% carbon content. The torsional fatigue limit was obtained by endurance tests and the tests due to a rapid method, i.e., the method of measuring temparature-rise. A surface rolling apparatus was designed specially for this investigation. Results obtained are as follows ; 1. The torsional fatigue limit may be increased greatly by surface rolling, and for this purpose it is desirable to roll at 550∼620 kg/mm2, (the maximum stress calculated by the hertz formula), and the larger value corresponds to the higher carbon content. 2. The maximum increment of torsional fatigue limit by rolling was about 27% independently of carbon content, but was smaller in heat-treated material. 3. The larger the surface rolling pressure, the larger the hardness of rolled surface, but it becomes nearly a constant value when the rolling pressure exceeds 550∼620 kg/mm2. 4. The rolling pressure under which the maximum torsional fatigue limit is obtained coincides with that causing the hardness of surface to approach a constant value.