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The growth behavior of stress corrosion cracking (SCC) of Alloy 600 with different cold-work levels was investigated in simulated boiling water reactors water environments. In addition, a correlation of cold-work levels, grain boundary characteristic, and the SCC growth behavior of Alloy 600 were studied. The results show that grains with high residual strain caused by cold work provide transgranular crack growth paths. The SCC growth rates of the specimens also increase with an increase in the degree of cold work and decrease remarkably after switching to the hydrogen water chemistry environment. Grain boundary character proves to be a factor more important than the localized strain concentration at the grain boundary in terms of its role in the intergranular crack growth rate of the Alloy 600 with a cold-work degree from 20% to 30%.

Crevice corrosion has become an important issue of the safety of AISI 304L austenitic stainless steel canister when exposed to the chloride environments located in coastal areas. Moreover, dust deposited on the canister surface may enhance the corrosion effect of 304L stainless steel. In this work, white emery was adopted to simulate the dust accumulated on the as-machined specimen surface. To investigate the effect of deposited white emery, chloride concentration, and relative humidity on the crevice corrosion behavior, an experiment was conducted on 304L stainless steel specimens at 45 °C with 45%, 55%, and 70% relative humidity (RH) for 7000 h. The surface features and crack morphology of the tested 304L stainless steel specimens were examined by SEM equipped with energy-dispersive spectrometry (EDS) and electron back scatter diffraction (EBSD). From the experimental results, a threshold RH for the stress corrosion cracking (SCC) initiation of AISI 304L austenitic stainless steel with different concentrations of chloride was proposed.

Stainless steels are used as canister materials for interim storage of spent fuel. Crevice corrosion has proved to be a safety concern of 304L stainless steel spent fuel canisters, when exposed to the saline environments of coastal sites. To study the effects of chloride concentration and test duration on the crevice corrosion behavior, and the effect of relative humidity on the initiation of discrete SCC cracks, a test program was conducted on the 304L steel specimens sprayed with synthetic sea water of 3.5 wt.%. The salt-deposited specimens, wrapped up with a crevice former to form a crevice configuration, were then exposed to an environment at 45 &deg, C with a pre-set 45%, 55%, and 70% relative humidity (RH), for 400 h and 10,000 h, respectively. The surface features and crack morphology of the tested 304L stainless-steel specimens were examined by energy-dispersive spectrometry (EDS) and electron back scatter diffraction (EBSD). For the specimens deposited with a chloride concentration of 1 g/m2, no cracks were found in the corroded regions after 400-h exposure, whereas SCC cracks were observed with the specimens tested for 10,000 h at all three pre-set relative humidity. The specimens tested at the pre-set relative humidity 45% are characterized with discrete SCC cracks, but, on the other hand, those exposed to the environments of 55% and 70% relative humidity show SCC cracks of distinct features. From the results of 10,000-h tests, it is inferred that the chloride concentration threshold for SCC initiation of 304L stainless steel at 45 &deg, C is between 0.1 g/m2 and 1 g/m2.

The purpose of this study was to evaluate the temperature fluctuation induced by electromagnetic stirring (EMS) and to investigate the influence of temperature fluctuation on the appearance and microstructure of the stainless steel welds. CF8A and 308L were used for the base metal and weld metal, respectively. Bead-on-plate welding (BOP) was conducted with a linear welding machine of gas tungsten arc welding (GTAW) with EMS. The experimental results show that EMS could prompt temperature alteration rates (TARs) to fluctuate between positive and negative, and enlarge the max/min ratios. Smaller ripples and surface roughness would be induced on the welds, while the dilution and the depth-to-width ratios both decreased. As a result, the ferritic and austenitic grains become more isotropic and their grain sizes become smaller.

Low-alloy steels used as structural materials in nuclear power plants are subjected to cyclic stresses during power plant operations. As a result, cracks may develop and propagate through the material. The alternating current potential drop technique is used to measure the lengths of cracks in metallic components. The depth of the penetration of the alternating current is assumed to be small compared to the crack length. This assumption allows the adoption of the unfolding technique to simplify the problem to a surface Laplacian field. The numerical modelling of the electric potential and current density distribution prediction model for a compact tension specimen and the unfolded crack model are presented in this paper. The goal of this work is to conduct numerical simulations to reduce deviations occurring in the crack length measurements. Numerical simulations were conducted on AISI 4340 low-alloy steel with different crack lengths to evaluate the electric potential distribution. From the simul...

The effects of heat treatments on the susceptibility to environment-induced cracking (EIC) of the CF8A stainless steel (SS) in simulated water of a boiling water reactor (BWR) were investigated by slow strain-rate tensile (SSRT) tests. Different microstructures were resulted by subjecting the as-casted CF8A to stress relief treatment (1050 °C/2 h, C sample), thermal aging (385 °C/20000 h, A sample), recovery annealing (500 °C/1 h, R sample) or solution annealing (1200 °C/2 h, S sample). The results indicated that after aging treatment (A sample), a decrease in tensile ductility and impact toughness was resulted relative to the un-aged specimens. Recovery annealing (R sample) caused an improved tensile ductility and impact toughness of the embrittled CF8A. Excessive solution (S sample) led to an obvious decrease in tensile strength but increase in ductility and toughness of the CF8A. The EIC susceptibility of the tested samples in simulated BWR water increased in the order: S

In the dry cask storage of spent nuclear fuels, a stainless-steel canister acts as an important barrier for encapsulating spent fuels. As a result, local corrosion behavior of 304L stainless steel has become an issue of concern in the wet coastal region and salt spray environment. The test was conducted after deposition of simulated sea salt particles on the 304L stainless-steel specimen. It was first covered with a crevice former, and then kept at 45 &deg, C with a relative humidity of 45%, 55%, and 70%, respectively. The surface morphologies and electron back scatter diffraction (EBSD) analysis of the corroded region for the 304L stainless-steel specimen are presented in this paper. The goal of this work was to investigate the crevice corrosion behavior of 304L stainless steel under different chloride concentrations and relative humidity conditions. From the experimental results, a threshold relative humidity for stress corrosion cracking (SCC) initiation of 304L stainless steel was proposed.

Stainless steel 304L (SS304L) has been selected as the material for canisters for spent fuel storage from three nuclear power plants in Taiwan. A crucial issue is extending the spent fuel storage safety standards of the canisters. The anti-saline corrosion abilities of three thermal spray coatings (i.e., Al, ZnAl, and 625 Inconel alloys) on the SS304L were evaluated by immersion in 3.5 wt % aqueous NaCl and with 0.025 g/cm2 NaCl deposition at 80 &deg, C and 80% relative humidity (RH) for 1000 h. The pristine thermal spray coatings were examined using the pull-off adhesion test to understand the adhesion strength, and Vickers hardness was measured for the mechanical properties of the three coatings. Confocal laser scanning microscopy (CLSM) was used to identify the porosities of the coatings. Furthermore, the surfaces of the specimens before and after corrosion were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The composition and distribution of the oxide layers formed on the coating surfaces during corrosion were evaluated. Electrochemical measurement was also performed with the polarization method to quantify the corrosion property of the three thermal spray coatings. The results showed that the corrosion rate of Al coating was lowest from the Tafel analysis after the 1000 h corrosion test in 3.5% aqueous NaCl. In contrast, the corrosion rate of Inconel 625 was lowest after 1000 h of the NaCl deposition corrosion test in a controlled environment. Therefore, the ZnAl thermal spray coating is a potential protection layer, keeping in mind economic considerations, of SS304L for anti-corrosion in saline environments.

In this study, Zn/15Al, Al and Inconel 625 coatings were applied on low carbon steel substrates by twin wire arc spray process as a corrosion and wear protection barrier against the marine atmosphere. The wear behavior of the coating layer was characterized by a pin-on-disk apparatus at a combination condition of three normal loads and two sliding speeds. The wear tests were conducted in a 3.5 wt.% NaCl solution to evaluate the wear resistance of the coatings in a corrosive environment. The results suggested that the Inconel 625 coating had a better wear resistance in a 3.5 wt.% NaCl solution as compared to the ZnAl and Al specimens. Zn/15Al coatings revealed less wear resistant in a corrosive environment due to the rupture of the oxide film on the coating surface during wear. For the sacrificial protection coatings of Zn/15Al and Al, the characteristics of surface oxide film play a vital role in the wear resistance of the coating materials.

This study was to investigate the synergetic effects of Mn and Nb on the microstructure and mechanical properties of Ni-based welds. The dissimilar weldments of Alloy 690 and SUS 304 L were welded with a manual shielding metal arc welding (SMAW) process. The weld metals were made of a core wire of Alloy 52 coated with fluxes of various Mn and Nb additions. The results showed that an increase in Mn could induce finer grains and smaller Nb-rich phases in the welds, while the dendrites and Mn-oxides became larger. For the welds with 3.99 wt.% Mn and 1.82 wt.% Nb, Nb-rich precipitates and Mn-oxides became smaller, and dendrites grew denser concurrently. The elongation of the welds at room temperature increased with the addition of Mn, but, by contrast, their hardness decreased. High contents of Mn and Nb could improve the notch strength and ductility at 300 °C, while they had little effects on the tensile stress at room temperature. Ductile ridges were the dominant fracture feature of the welds with an addition of Mn. For the welds with 3.99 wt.% Mn and 1.82 wt.% Nb, ridges dotted with small and deep dimples became prevalent. Keywords: Mn, Nb, Shielding metal arc welding, Tensile test

In this research, some nondestructive ultrasonic techniques were employed to inquire into the effect of microstructural changes induced by thermal aging and cold work on the ultrasonic response. As thermal embrittlement is a risk to the safety of nuclear power plants, a nondestructive detection method has to be developed for on-site monitoring. The austenitic stainless steel with &delta, ferrite specimens were used to study the behavior of microstructural changes caused by age-treating and cold work and then examined by the velocity, attenuation, and nonlinear ultrasonic technique. The variations of the linear and the nonlinear ultrasonic parameters were related to the microstructural changes. Additionally, the experimental results suggest that the ultrasonic nonlinearity parameter of cast stainless steel is determined by the microstructure evolution caused by spinodal decomposition and the phase precipitation process.

In this study, thermally sprayed Inconel 625 coatings were used to improve the corrosion-wear resistance of 304L stainless steel substrates in saline environments. The tribological behavior of various Inconel 625 coatings obtained through flame spraying (F), arc spraying (A), plasma spraying (P), or high-velocity oxygen fuel spraying (H) was evaluated by testing the specimens on a pin-on-disk apparatus with a cup-shaped container that was filled with a 5 wt% NaCl solution or deionized (DI) water. The results indicated that regardless of the testing solution, the corrosion-wear resistance of the Inconel 625 coating specimens was in the order F > A > P > H. Microstructural examination revealed that the oxide within the as-sprayed Inconel 625 coating layer was mainly Cr2O3 and exhibited a higher hardness but lower elastic modulus than the Ni-based matrix. The oxide within the Inconel 625 coating layer is suggested to function as an antiwear phase against the corrosive-wear environment. The high corrosion-wear resistance of the F specimen was attributed to the high oxide content within its coating layer. In addition, all Inconel 625 coatings exhibited higher wear resistance in the 5 wt% NaCl solution than in the DI water, which implied that chloride lubricated the sliding wear, considerably reducing weight loss of the coating after corrosion wear.

This study investigated the effects of dendrite axis and fusion boundary (FB) on the stress corrosion cracking (SCC) of 308 L/304 L welds by using an alternating current potential drop (ACPD) technique to measure the SCC growth rates in a simulated boiling water reactor environment. The results show that the ferrite/austenite interfaces are more susceptible to SCC in the SS 308 L welds. Furthermore, the angle between the applied load and the dendrite axis affects the SCC growth rate, and as this angle approached 90°, the SCC crack growth rate increases. The SCC cracks in the heat affected zone (HAZ) are mainly intergranular and some cracks propagate transgranularly. Furthermore, the primary crack in the HAZ propagates along the FB; when reaching FB, some secondary cracks are arrested at the FB. The residual strain caused by weld shrinkage is the crucial factor for the increase in SCC susceptibility in HAZ.

In this study, thermal simulation was performed to conduct thermal cycles on CF8A cast austenitic stainless steel substrates with different ferrite contents to simulate the microstructures that form near a weld fusion boundary. The effects of ferrite content and morphology on the mechanical properties of CF8A were investigated. The stress corrosion cracking (SCC) susceptibility of the specimens was evaluated with slow strain rate tensile (SSRT) tests in a simulated boiling water reactor (BWR) coolant environment. The results indicated that an increase in the ferrite content of the CF8A base metal led to a minor increase in hardness. Thermal simulation caused a marked increase in ferrite content, especially in the high ferrite CF8A substrate. The yield strengths of the tested samples increased obviously with increasing ferrite content, but the ductility decreased. The ultimate tensile strengths of the samples reached a plateau when the ferrite number (FN) was greater than 18. The applied thermal simulation greatly improved the impact toughness of high ferrite CF8A in comparison with the original substrate. The results indicated that the samples with high ferrite content had a shorter rupture life but greater fracture strength than those with low ferrite content strained in high temperature water. Moreover, cleavage-like fracture was found in all of the samples that suffered from SCC. The SCC cracks were observed to be more likely to propagate along the δ/γ interfaces of a CF8A. Furthermore, crack initiation and growth inside the γ of low ferrite CF8A contributed to a great loss in strength in a high temperature water environment.

Cast austenitic stainless steel (CASS) often contains high contents of silicon, phosphorus, and sulfur to prompt low melting phases to form in the welds. As a result, welding defects can be induced to degrade the welds. This study&rsquo, s purpose was to investigate the effects of electromagnetic stirring (EMS) on the CASS weldments. The results showed that the ferrites in the heat affected zone (HAZ) had tortuous grain boundaries, while those that were close to the fusion lines had transformed austenites. EMS could reduce the influence of the welding heat to make the grain boundaries less tortuous and the transformed austenites smaller. Although their temperature profiles were almost the same, the gas-tungsten-arc-welding (GTAW) weld had smaller grains with massive ferrite colonies and more precipitates, while the GTAW+EMS weld had denser ferrite colonies with multi-orientations, but fewer precipitates. The hardness of the base metals and HAZs were typically higher than that of the welds. For both of the welds, the root was the region with the highest hardness. The hardness decreased from the root to the cap regions along the thickness direction. The GTAW weld had a higher hardness than the GTAW+EMS weld. At room temperature, the GTAW+EMS weld had a higher notched tensile strength and elongation than the GTAW weld. This could be attributed to the observation that the GTAW+EMS weld had dense and intersecting dendrites and that more austenites were deformed during tensile testing.

Longitudinal and transverse cracks were observed to occur on the surface of Norem hardfacing welds for a period of time after welding. The welds were mainly cracked by hot cracking. To prevent the weld from cracking, a hammer peening process was employed to mitigate its tensile stress. A scanning electron microscope (SEM), equipped with the electron backscatter diffraction (EBSD) capability, was used to study the phase and carbide distribution in the weld. The results showed that the hammer peening process could help prevent crack propagation by reducing the welding residual stress and inducing a great number of low angle grain boundaries. The microstructures and micro-hardness of the peening-treated welds are also compared to the as-welded specimens in this paper to demonstrate the efficacy of the peening process to prevent weld from cracking.

The slow strain rate tests (SSRT) at a nominal strain rate 1× 10−6/s were conducted to evaluate the mechanical properties of CF8A cast austenitic stainless steel (CASS) in air and high-temperature water environments. CF8A CASS is mainly composed of a matrix of γ phase dispersed with δ ferrites and is affected slightly by aging heat treatment. The hardness value of γ phase did not change with aging time, while that of δ ferrite increased with increasing the aging time. The SSRT results showed that a loss in elongation of a high δ-ferrite specimen was more significant than that of the low δ-ferrite specimens. The SCC paths of the low δ-ferrite specimen were along the links between δ ferrites dispersed in the matrix. For the high δ-ferrite specimen, most of the cracks were observed to propagate through the chromium depletion regions in the ferrite grains, which were preferentially oxidized during the SSR test in water. However, the elongation did not decrease further after aging time was longer than 2,400 h,...

The influence of heat input on stress corrosion cracking (SCC) in the heat-affected zone (HAZ) of A508 steel welds was investigated. Constant extension rate tensile tests were conducted on notched round-bar specimens in simulated reactor coolant conditions to assess SCC performance. In multi-pass welds, the use of a low heat input resulted in a better SCC resistance than that of a high heat input due to the existence of a more refined microstructure.

The purpose of this paper was to investigate the effects of Nb on the microstructure and elevated-temperature mechanical properties of Alloy 690-SUS 304L dissimilar welds. The results show that the welds were dominant with dendrites and interdendritic phases. In the low Nb welds, the main interdendritic phases were Nb-rich and Al-Ti-rich phases. Cr-carbides were precipitated along the grain boundaries of the root region. In the high Nb welds, there were large Nb-rich phases in the cap region, while smaller Nb-carbonitride precipitates were found in the root region. The addition of Nb increased the hardness of the fusion zones. At 300 � C, though the tensile strengths of all welds were higher than that of 304L, micro-cracks were unexpectedly found in the low Nb weld. Notched specimens were tested to characterize the mechanical properties of the welds. Both of the yielding and tensile strengths of the welds increased with Nb additions. On the fracture surface, the brittle fracture features also became noticeable. [doi:10.2320/matertrans.MRA2008008]

High-cycle fatigue tests were conducted to investigate the effects of temperature, stress ratio (R), specimen orientation, welding and specimen size on the fatigue behavior of type 316L stainless steel. The high-cycle fatigue test results indicated that the fatigue limits significantly decreased when the stress ratio (R) decreased. The corresponding fatigue limits were reduced to lower values when tests were conducted at 300 � C, compared to those obtained at room temperature. The fatigue behavior and fatigue limits of standard and subsize specimens were observed to be consistent at both room temperature and 300 � C. The constant life diagram was established from the S–N curves acquired. The fatigue limit strongly depended on the materials strength, which was a function of specimen orientation, test temperature, and welding processes. The dimension of the fatigue damaged area on a fracture surface increased as the stress ratio decreased. In the case of R ¼� 1:0, the fatigue damaged region extended over the whole fracture surface. The subgrain boundaries after high-cycle fatigue tests were clearly demonstrated by their diffraction patterns, which were related to the dynamic recovery of multiple dislocations.

Anterior chest burns in young females frequently result in complicated problems such as scar contracture, damage to the nipple–areolar complex and breast tissue. Furthermore, an absent breast mound, hypoplasia or disfigurement of developed breasts can result in breast asymmetry and psychological problems. So we presented an alternative procedure that combines burn scar reconstruction and augmentation mammaplasty performed during one operative session. We believe patients who have either smaller natural breasts or burned breast with anterior chest scar contracture can earn both functional and aesthetical benefits via this simultaneous operation.