Nondestructive Evaluation of Thermally Degraded 2.25Cr-1Mo Steel by Electrical Resistivity Measurement

Abstract

An attempt was made to evaluate nondestructively the degradation of thermally aged 2.25Cr-1Mo steel by electrical resistivity measurement. Artificial aging was performed to simulate the microstructural changes in 2.25Cr-1Mo steel arising from long time exposure at 540 C. Microstructural parameter (amount of dissolved Mo in the matrix), mechanical property (ductile-brittle transition temperature) and electrical resistivity were measured to investigate the relationship among these parameters. Both the amount of dissolved Mo and the electrical resistivity decreased rapidly in the initial 1000 hours of aging and then changed little thereafter. On the other hand, the ductile-brittle transition temperature (DBTT) increased rapidly in the initial stage of aging and then saturated afterward. Electrical resistivity was found to have linear correlation with the amount of dissolved Mo and DBTT, respectively. Electrical resistivity was suggested as a potential nondestructive evaluation parameter for assessing DBTT of the thermally degraded 2.25Cr-1Mo steel.

Magnetic Evaluation of Microstructures and Strength of Eutectoid Steel

“…There are increasing needs to introduce nondestructive evaluation techniques for better time saving and economic quality control of steel products. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Magnetic, [1][2][3][4][5][6][7][8] Barkhausen noise, [9][10][11][12] ultrasonic 13) and electrical resistivity 14) methods have been applied to evaluate material properties nondestructively. Magnetic method, by which correlations between material properties and magnetic parameters such as coercivity, remanence, hysteresis loss and saturation magnetization can be obtained, is applicable to various kinds of ferromagnetic steels.…”

Correlation of Magnetic Barkhausen Emission Profile with Strength of Thermally Degraded 2.25Chromium–1Molybdenum Steel

“…2 can be attributed to the coarsening of carbides due to thermal exposure and the depletion of solution hardening elements. 1) Typical MBE profiles of the as-received and thermally degraded specimens are shown in Fig. 3.…”

“…There have been extensive studies on the microstructural and mechanical characterizations of 2.25Cr-1Mo steel degraded at elevated temperatures. [1][2][3][4][5] For in-situ damage monitoring of structural steel components used at elevated temperatures, several non-destructive evaluation (NDE) techniques such as electrical resistivity, ultrasonic wave, and magnetic Barkhausen emission (MBE) method [6][7][8][9][10][11][12] have been applied. MBE, which is induced by rapid change in magnetic flux due to discontinuous movement of domain walls, has been considered for a NDE technique owing to its measurement convenience and high sensitivity to microstructural changes.…”

Compensation of the Skin Effect in Low-Frequency Potential Drop Measurements

“…Four electrodes are connected to the surface of a conducting component, current is injected through two of the electrodes while the potential difference is monitored across the remaining two electrodes, the electrical transfer impedance is then calculated. Usually resistance, the real part of impedance, is used to infer changes in geometry arising from component strain [6,7] or defect growth [8][9][10], or less frequently changes in electrical conductivity [11,12].…”