Papers by Keyword: 2.25Cr-1Mo Steel

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Authors: B.B. Jha, Barada Kanta Mishra, S.N. Ojha
Abstract: Acoustic emission (AE) signals, obtained during the isothermal oxidation of 2.25Cr-1Mo steel at 773 K, 873 K, 973 K and 1073 K, have been analyzed. The results indicated that the rate of occurrence of AE events and consequently the total number of AE events generated during isothermal oxidation at these temperatures increased with an increase in the oxidation rate. Variation in the temperature of oxidation did not show any variation in the root mean square (RMS) level of the AE signals. The b-parameters obtained from a logarithmic cumulative amplitude distribution plot indicated that the strength of the AE signals did not change during isothermal oxidation carried out at these temperatures. Different event rates, and consequently the difference in the total number of AE events generated during isothermal oxidation at these temperatures, are indicative of the increased rate of energy release associated with the growth of oxide layers formed at higher temperatures. The rate of energy release has been found to be higher for higher temperatures of oxidation.
Authors: Jai Won Byeon, S.I. Kwun, Kae Myung Kang
Abstract: In this study, mechanical degradations in 2.25Cr-1Mo steel were evaluated by quantitative morphological analysis of carbides. Based on the morphology, carbides were classified as globular, fine acicular, rod, and grain boundary one. Mean size of carbides were determined as a function of morphology and thermal degradation time at 630°C. Area fraction of grain boundary carbides and fraction of grain boundary M6C carbides were observed to increase rapidly in the initial stage of degradation and then gradually afterwards. Both mean size of globular carbide and fraction of grain boundary M6C carbides were linearly correlated with strength. Potentials of carbide morphology analysis as a health monitoring technique were discussed, in term of correlation coefficient with strength.
Authors: B.B. Jha, T.K. Sahoo, D. Tripathy, Barada Kanta Mishra
Abstract: Miniature specimen techniques viz. small-punch tests (SPT) have been carried out at room temperature in order to correlate the microstructural degradation of 2.25Cr-1Mo steel with that of SPT parameters. Microstructural degradation of this steel has been introduced as a result of thermal ageing corresponding to Larson-Miller parameters (LMP) values of 33,012, 35,402, 37,846 and 38,374. SPT parameters viz. total area and area under the region of plastic instability of the load-displacement curve have been found to decrease with an increase in LMP values. A strength parameter viz. UTS obtained using uniaxial tensile tests has also been found to decrease with an increase in LMP values. The results indicated that miniature specimen techniques viz. small-punch test could be successfully used to assess the degradation of microstructures in 2.25Cr-1Mo steel generated due to their exposure to high temperatures.
Authors: Seung Hoon Nahm, Jeong Min Kim, Jong Seo Park, Kwang Min Yu, Dong Kyun Kim, Am Kee Kim, Dong Jin Kim
Authors: Jong Seo Park, Un Bong Baek, Jeong Min Kim, Seung Hoon Nahm, Bong Young Ahn
Abstract: Several nondestructive evaluation methods were attempted for the estimation of the creep damage of degraded 2.25Cr-1Mo steel. The specimens of three different aging periods were prepared by an isothermal heat treatment at 430°C, 482°C, and 515°C. The effect of probe configuration on the electrical resistivity was studied. Single configuration method and dual-configuration method were utilized for measuring electrical resistivity. The electrical resistivity was determined by a standard DC four-point probe method at 24±0.5°C. Indentation test, magnetic characteristics test and ultrasonic test were carried out to investigate the correlation between the major characteristics and aging parameter. Unlike the electrical resistivity characteristics, ultrasonic attenuation coefficient and indentation characteristics did not show a relation to Larson-Miller parameter. However, a correlation between the electrical resistivity and aging parameter was identified, which allows one to estimate the extent of material degradation.
Authors: B.B. Jha, Barada Kanta Mishra, T.K. Sahoo, P.S. Mukherjee, S.N. Ojha
Abstract: The present paper investigates the effect of microstructural variations upon the wear properties of 2.25Cr-1Mo steel using a dry sliding wear test. Optical, Scanning and Transmission Electron Microscopy (TEM) together with Energy Dispersive X-ray analysis (EDX) have been used to characterize the microstructures and identify the evolution of various precipitates in terms of their shapes, sizes and morphologies. The wear behavior of this steel was investigated using a disc-on-roller multiple wear tester under dry sliding conditions, rubbing against EN-31 steel. Samples were tested at 100N load and 500rpm sliding speed at room temperature. A decrease in wear loss was measured continuously for up to one hour for all the samples. The results indicated that the wear behavior of this steel was highly influenced by microstructural variations taking place during service exposure. The precipitation of globular Cr- and Mo-rich carbides has been found to improve the wear behavior of this steel at room temperature. Scanning Electron Micrographs (SEM) of worn surfaces have been used to correlate the results obtained
Authors: Hyo Jin Kim, Do Won Seo, Jae Kyoo Lim
Abstract: Steam generator began having severe problems 20 years ago. The main causes were wastage, wear, loose parts, denting. These problems were solved by changing the water chemistry treatment method. Therefore these damage types were replaced by stress corrosion cracking on the inner surface of the tubes and most recently by intergranular attack and stress corrosion cracking on the external surface of the tube. Steam generator has experienced various forms of damage, most involving some kind of corrosion. Some of these problems have been virtually eliminated, others are successfully managed, but a few have not yet been brought under control. This study is to evaluate the environmental effects on the susceptibility to stress corrosion cracking in Cr-Mo alloy under simulated crevice condition. The test is simulated by producing drop, wet and evaporation process. The XRF measurement is performed to investigate the amount and distribution of chromium carbide of grain boundaries. The tests are performed in the alkalic and acidic solution under various strain rates.
Authors: Seung Hoon Nahm, Jong Seo Park, In Hyun Chung, Kwon Sang Ryu, Am Kee Kim
Abstract: Many researchers have been interested in the nondestructive measurement methods for examining the microstructural changes and components damage in order to assure the safe operation of steel structure. It has been recognized that the techniques based on magnetic measurement offered a great potential because of high susceptibility to the change of several metallurgical factors. In this study, the effect of isothermal heat treatments, which simulate the microstructural changes observed in reactor vessel material at the service temperature, on the magnetic properties was investigated. 2.25Cr-1Mo steel specimens with several different kinds of aging were prepared by an isothermal heat treatment at three different temperature levels. Magnetic property such as coercive force was measured. The coercive force at room temperature monotonously increased with the extent of degradation of the material. The correlation between the measured magnetic property and the mechanical properties was studied. In addition, the applicability of magnetic properties measurements to the evaluation for toughness degradation of reactor vessel was discussed.
Authors: Jai Won Byeon, C.S. Kim, S.I. Kwun, S.J. Hong
Abstract: It was attempted to assess nondestructively the degree of isothermal degradation of 2.25Cr-1Mo steel by using high frequency longitudinal ultrasonic wave. Microstructural parameter (mean size of carbides), mechanical property (Vickers hardness) and ultrasonic attenuation coefficient were measured for the 2.25Cr-1Mo steel isothermally degraded at 630°C for up to 4800 hours in order to find the correlation among these parameters. The ultrasonic attenuation coefficients at high frequencies (over 35MHz) were observed to increase rapidly in the initial 1000 hours of degradation time and then slowly thereafter, while the ones at low frequencies showed no noticeable increase. Ultrasonic attenuation at high frequencies increased as a function of mean size of carbides. Ultrasonic attenuation coefficient was found to have a linear correlation with the hardness, and suggested accordingly as a potential nondestructive evaluation parameter for assessing the mechanical strength reduction of the isothermally degraded 2.25Cr-1Mo steel.
Authors: A.M. Guo, Z.X. Yuan, W.X. Yuan
Abstract: The influence of trace boron and cooling rate on the thermal embrittlement of 2.25Cr -1Mo steel was investigated by thermo-mechanical simulator and SEM analysis. It was proved that the trough in the thermo-ductility curve located between 1000°C and 700°Cand shifted to lower temperature and the temperature range of the trough became shallow and narrow as the boron content increased. When the cooling rate decreased, the ductility trough became shallow and narrow too. This made the steel free of surface crack in CC process.
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