Evaluation of the Microstructural Changes of a Heat Treated 2.25%Cr-1%Mo Steel using EMAT and Ultrasonic Testing

The microstructural changes in a heat treated 2.25%Cr – 1%Mo steel were evaluated by using NDT/NDE and electron optics techniques. The continuous improvements in ultrasonic transducer technology and signal processing make the use of Immersion UT and Electro Magnetic Acoustic Transducers (EMAT) a feasible non-destructive testing techniques to assess different levels of microstructural changes in complex alloys systems. For example, in this study the different microstructural conditions resulting from a number of heat treatments, i.e. annealing, water quenched, spheroidization and tempering, were systematically evaluated using a combination of signal processing results such as; ultrasonic attenuation, peak amplitude. The NDT/NDE results were complemented with the use of optical and scanning electron microscopy. Correlations between the different microstructures; a) ferrite-pearlite; b) martensite; c) spheroidized Fe3C carbides and alloyed Cr-Mo carbides and the signal processing results were developed. In addition, microhardness and CVN testing of the different microstructural conditions were also evaluated. The results of this study will be presented and discussed.

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