Development of small sensor and system for measurement of retained austenite

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Alloyed white cast irons produce a large amount of retained austenite when they are cast or quenched. The retained austenite affects severely the mechanical properties of the products and the defect of the parts. Therefore, the control of amount of retained austenite in the cast irons is very important. X-ray diffraction method has been used for a measurement of retained austenite. A development of a brief measurement method of retained austenite and its evaluation system has been expected. In this study, many samples including different amount of retained austenite for nine kinds of cast irons were prepared by changing the heat treatment condition and the change in the magnetic properties of these samples were measured nondestructively using a newly developed small sensor with the exciting coil and search coil measuring about 20^Lx25^Wx20^Hmm in size like a Japanese syllabary「コ」. The amount of the retained austenite in the cast irons could be estimated by detecting the change of induced voltage associated with change in amount of retained austenite.