X-ray method of measuring retained austenite in heat treated white cast irons

An X-ray technique for measuring the amount of retained austenite in textured alloys has been successfully applied to white cast irons. The technique involves rotating and tilting the sample about the incident X-ray beam such that every grain on the sample surface, no matter what its orientation, contributes to the diffraction intensity. The theoretical relationship between the amount of retained austenite and the intensity ratios of austenite and martensite/ferrite diffraction lines is explained. It is shown that the rotating and tilting does not necessarily produce a diffraction pattern absolutely free of preferred orientation from a single crystal; however, it is experimentally demonstrated that the technique eliminates enough of the preferred orientation from the diffraction pattern that the method can be used for cast alloys. The effect of scanning speed and time constant are discussed with reference to the quality of the diffraction pattern. Other techniques of retained-austenite measurement, i.e., some conventional X-ray methods, both optical and electron metallography, and magnetometry, are discussed and claimed less suitable for cast alloys such as white cast irons. Examples are given of the effect of heat treatment of white iron rolling mill rolls on the retained austenite in these rolls.