The fracture behavior of the white layer on the cast steel brake disc in bending fatigue was evaluated using the acoustic emission (AE) method to analyze the fracture mechanical characteristics. The fatigue strength of the disc material including the white layer tended to be lower than that of the unused material. It was found that the AE signal of the unused material occurred continuously while the white layer occurred suddenly. This clarifies that the fracture of the white layer is brittle. These results indicate that heat cracking occurs easily on the white layer.
