<p>The objective of this project was to evaluate the feasibility of thermoelectric (TE) NDE for distinguishing between Grade 91/92 steels with microstructural characteristics that lead to acceptable and poor performance in service. &nbsp;TE NDE is highly sensitive to certain microstructural changes in metal alloys and, at the same time, uniquely insensitive to the geometrical features of the components under test, therefore could potentially be used for industrial manufacturing quality control and to assess the condition of installed components.&nbsp; Sixteen small-diameter thin-wall tube and eight large-diameter thick-wall pipe section specimens made of Grade 91/92 martensitic steel were tested in this study.&nbsp; These specimens represented eight heat treatment conditions used to control the microstructure of the samples resulting in Vickers hardness levels between 147 and 428 HV.&nbsp; These specimens were characterized by a high-precision automated four-point thermoelectric power (TEP) measurement system developed at the University of Cincinnati.&nbsp; Compared to commercially available two-point TEP measurement devices, this novel thermoelectric NDE technique offers higher repeatability and absolute accuracy without the need for empirical calibration.&nbsp; Thermoelectric measurements conducted on both tubes and pipe sections exhibited the same trend of decreasing TEP in the 10.8−13.2 µV/°C range with increasing hardness.&nbsp; The main conclusion of this investigation is that the normalized and heat affected zone microstructures of Grade 91/92 martensitic steels, which produce significantly elevated hardness levels, can be easily identified by TEP measurements.&nbsp; In addition, the over tempered microstructure, which does not exhibit significantly elevated hardness level, could also be identified in the two tube specimens, but not in the single pipe specimen tested in this study.</p>

Microstructure Characterization in Martensitic Steels Using Thermoelectric Nde

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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