Assessment of material thermal history in elevated temperature components

The extraction replica technique provides a valuable nondestructive metallographic tool both for monitoring microstructural changes caused by material aging and for quantitatively assessing the thermal history of material in components operating in creep regime. It has been, in fact, verified that the chemical composition of carbides collected on replicas is correlated both to temperature and to time of exposure of the material. In this report, the infield application of the replica technique is described, focusing on the quantitative evaluation of exposure temperature of a 214Cr1Mo steel. The validity of the technique has also been verified for 9–12% Cr ferritic steels after long-term creep exposure in laboratory tests; also in this case, on the basis of the available data, a correlation between the CrFe ratio in M23C6 carbide and the Larson-Miller parameter appears promising.