Retained austenite determination

As in the case of corrosion failures, the sequence of steps involved in analyzing wear failures are initial examination of the failed component including service conditions to establish the mode or combination of modes of wear failure, metallographic examination to check if the microstructure of the worn part met the specification, both in the base material and in the hardened case or applied surface coatings, existence of localized phase transformations, shear or cold worked surfaces, macroscopic and microscopic hardness testing to determine the proper heat treatment, X-ray and electron diffraction analysis to determine the composition of abrasives, wear debris, surface elements and microstructural features such as retained austenite, chemical analysis of wear debris surface films and physical properties such as viscosity and infrared spectral determination of the integrity of lubricants and abrasive characteristics of soils or minerals in the cases of wear failures of tillage tools. 

The sensitivity of the x-ray method in determining small amounts of retained austenite is limited chiefly by the intensity of the continuous background present. The lower the background, the easier it is to detect and measure weak austenite lines. With filtered radiation the minimum detectible amount is about 2 volume percent austenite, and with crystal-monochromated radiation probably about 0.2 percent. The error in the austenite content, originating in the calculation of R and the measurement of I, is probably about 5 percent of the amount present, in the absence of preferred orientation (Sec. 14-12). 

The areas of application of quantiative X-ray powder diffraction are many and varied. Many hundreds of analysts are using this technique on a daily basis. Some of the more common applications would include ore and mineral analysis, quality control of rutile/anatase mixtures, retained austenite in steels, determination of phases in airborne particulates, various thin-film applications, study of catalysts, and analysis of cements. The current state of the art in the quantitative analysis of multiphase materials is that accuracies of the order of a percent or so can be obtained in those cases where the particle orientation effect either is nonexistent or has been adequately compensated for. 

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