Toru Goto

Changes in electromagnetic properties during thermal aging of duplex stainless steel

Abstract To maintain the integrity of applications of duplex stainless steels currently in service, a study using two types of electromagnetic testing, i.e. electric resistivity testing and coercivity measurement testing, was conducted to develop a method to nondestructively estimate their Charpy-impact energy at room temperature. Materials tested included four grades of duplex stainless steel with differing ferrite content that had been subjected to long-term heating. Changes in Charpy-impact energy and electromagnetic properties due to aging were observed. It was found that electric resistivity and coercivity are reliable indicators of the process of embrittlement, but their relationship to impact energy is dependent on the material. Further, the dependency on the material differed between the two testing methods employed, though the main cause of embrittlement for duplex stainless steels can be assumed to be ferrite phase separation. Coercivity testing seems to show the property change in the ferrite phase more sensitively than it shows the difference in material, whereas electric resistivity testing distinguishes the difference in material more clearly than the property change in the ferrite phase. Change in Charpy-impact energy due to embrittlement is mainly caused by ferrite phase separation, but Charpy-impact energy is also influenced by the austenite phase. As the conclusion of this study, an equation involving electric resistivity, coercivity and ferrite content was presented as a method applicable to the nondestructive estimation of Charpy-impact energy at room temperature.

Quantitative Residual Strain Analyses on Strain Hardened Nickel Based Alloy

Many papers have reported about the effects of strain hardening by cold rolling, grinding, welding, etc. on stress corrosion cracking susceptibility of nickel based alloys and austenitic stainless steels for LWR pipings and components. But, the residual strain value due to cold rolling, grinding, welding, etc. is not so quantitatively evaluated.

X-Ray Study on Deformation and Fracture of Solid. Influence of Detector Misalingnment on the .OMEGA. Assembly X-Ray Stress Measurement Using a Position Sensitive Proportional Counter as a Detector.

Recently, the position sensitive proportional counter (PSPC) has been becoming popular as a detector for the X-ray stress measurement. However, little information is available in the literature regarding the effects of systematic errors such as specimen mis-setting, collimator misalignment and detector misalignment etc. on the stress measurement using the PSPC.In this paper, the detector misalignment is discussed using a model and a simulation method of the Ω assembly X-ray stress measurement. The stress errors Δσrd, Δσtd and Δσkd due to the translation rd in the direction of goniometer radius, the translation td in the direction of diffraction angle and the rotation kd, respectively, were calculated as the value of measured stress σx subtracted by specimen stress σ and intrinsic stress σc.It was found that Δσrd, Δσtd and Δσkd are expressed as a linear relation of rd, td and kd, respectively. The slope of the relation depends on the collimator dimensions, goniometer radius and specimen stress. However, the absolute value of Δσrd, Δσtd and Δσkd were found extremely small for the conditions examined. If the detector is misaligned under the combination of translations and rotation, the stress error is the sum of the errors due to translations and rotation. If the stress is measured under detector misalignment with specimen mis-setting, the stress error is the sum of the errors due to detector misalignment and specimen mis-setting. Under the detector misalignment with collimator misalignment, the stress error is the sum of the errors due to detector misalignment and collimator misalign-ment. It was concluded that the stress error due to detector misalignment is negligibly small when compared with those due to specimen mis-setting and collimator misalignment.

Influence of Specimen Mis-Setting to the .OMEGA. Assembly X-Ray Stress Measurement Using a Position Sensitive Proportional Counter as a Detector.

Recently, the position sensitive proportional counter (PSPC) has been becoming popular as a detector for X-ray stress measurement. However, little information is available in the literature regarding the effects of specimen mis-setting on the stress measurement using the PSPC.In this paper, a modeling of the Ω assembly X-ray stress measurement using a PSPC as the detector is presented enabling us to simulate the stress measurement under the various conditions including specimen mis-setting. As the results of simulation, it was found that the use of collimator yields an apparent stress (intrinsic stress), and that the absolute value of the stress increases with the increase in the width of the collimator and decreases with the increase in its effective length. It was also found that the error in stress measurement due to specimen mis-setting is expressed as a linear relation of the ratio L/R0 (L: offset of mis-setting, R0: goniometer radius), and that the coefficient in the relation is given as a function of secondary order of the ratio 2bψ/Cl (2bψ: width of collimator, Cl: effective length of collimator).

Influence of Specimen Missetting to the X-ray Stress Measurement in the Case of Side Inclination Method Using Position Sensitive Proportional Counter as Detector.

Recently, the position sensitive proportional counter (PSPC) is becoming popular as the detector for the X-ray stress measurement. However, the author considers that the characteristics of the X-ray stress measurement using PSPC are not yet studied enough. In this paper, the influence of specimen missetting to the X-ray stress measurement is discussed based on the results investigated as one of the factors affecting the influence of computer simulation and experimental studies for the case of side inclination method. The size of collimator is also. As the results, it was found that the error in stress measurement is proportional to the ratio L/R0 (L; offset of missetting, R0; goniometer adius). About 25MPa of the error occurs at L/R0=0.0025 in the case of the measurement of ferrite sample using Cr target. The size of collimator has little effect to the relation between the error and L/R0.

Fatigue Life Assessment of High-Temperature Cr-Mo-V Rotors by X-ray Diffraction

ABSTRACT In order to predict the initiation life of peripheral groove cracks in high-temperature rotors at a fossil power plant, a study using X-ray diffraction was conducted. A diagram for estimating the fatigue life fraction is presented, based on the following findings: (1) The half-value breadth of the X-ray diffraction line generally decreases with the increase in fatigue damage for Cr-Mo-V rotor material at about 500°, which is the usual operating temperature. (2) For constant-strain cycling, it is possible to express the change of half-value breadth by a straight line against the logarithm of the number of cycles when the early part of life is neglected. The slope of the line remains almost constant, independent of the strain range. Also, the relationship between the half-value breadth and the number of cycles to crack initiation can be expressed by using a straight line with semi-log plotting. (3) For two-stage multiple-strain cycling and strain cycling with a holding time, it is also possible to express the change of half-value breadth by a straight line with the same slope as that found for constant-strain cycling. In order to express the relationship between the half-value breadth and the number of cycles to crack initiation, the same straight line as that found for constant-strain cycling can also be used.

Nondestructive Evaluation of Temper Embrittlement in Turbine Casing Steels.

In order to develop a nondestructive method of evaluating embrittlement for turbine casing steels, a study was conducted using lab-charged P-doped steels. P-doped steels showed evident embrittlement due to segregation of P at grain boundaries. The chemical etching test used was found to be a very good measure of embrittlement for casing steels. There was a good correlation between the width W of the etched grain boundary measured by the penetration of replicas and FATT. The correlation between W and FATT was also recognized for the samples taken from long-term-serviced casings. Multiple regression analysis was conducted in order to express FATT using W and other variables which are known or nondestructively measurable. The regression equation obtained gave an estimate of the actual FATT with the scatter of ±20°C. On the basis of this result a nondestructive evaluation method of temper embrittlement for turbine casing is proposed.