Observation of Microstructures in Carburized-Quenched SCM415 Steel under Rotating Bending Fatigue of 716 MPa

Abstract:

Carburized-quenched steel has a hard layer on the surface and a soft layer in the core. Internal fatigue cracks are observed around the boundary between these two layers under cyclic stress. In this research, we investigated the microstructures (carbon content, prior austenite grains and retained austenite) in the carburized-quenched chromium molybdenum steel bar (JIS-SCM415, diameter = 10 mm) failed by rotating bending test (RBT) at nominal stress amplitude of 716 MPa. After the investigations, we obtained three conclusions: the carbon content in the area from the surface to 0.1 mm depth was higher than other area; the prior austenite grain (PAG) sizes at 0.1 mm depth from the surface was almost the same as that of 0.6 mm depth; and the retained austenite which was indicated from the ratio of γ to α in the cross section ranging from the surface to 0.1 mm depth was decreased by rotating bending fatigue.

• Periodical: Materials Science Forum (Volume 1084)
• Pages: 97-102
• DOI: https://doi.org/10.4028/p-70dgq7
• Online since: April 2023
• Authors: Shusuke Kita, Kei Ushizima, Takahiro Matsueda, Koshiro Mizobe, Katsuyuki Kida*
• Keywords: Carbon, Carburizing, Retained Austenite, Rotating Bending Fatigue, SCM415 Steel

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