• Journal of Welding and Joining
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• v.32 no.6
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• pp.70-74
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• 2014

On this study, we researched the in-process monitoring during fiber laser welding as well as on the first paper. On the previous/formal study, we analyzed the change of emission signal on thin plate welding. On this study, however, we analyzed RMS and FFT with emission signals in laser welding on lap joint and butt joint of 8mm-thick 316L stainless steel. As the result, the movement of specific frequency peak was observed according to welding speed changes. Furthermore, frequency peak as a result of FFT on the thick plate welding are much clearer than on the thin plate welding. Therefore, it is expected that the welding parameter changes can be predicted in case of applying FFT to in-process monitoring.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.5
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• pp.750-757
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• 2003

In order to determine creep stress intensity limit of high-temperature components, the usefulness of the creep work and time equation, defined as W$\_$c/t$\^$p/ = B(where W$\_$c/ = $\sigma$$\varepsilon$ is the total creep work done during creep, and p and B are constants), was investigated using the experimental data. For this Purpose, the creep tests for generating 1.0% strain for commercial type i16 stainless steel were conducted with different stresses; 160 MPa, 150 MPa, 145 MPa, 140 MPa and 135 MPa at 593$^{\circ}C$. The plots of log W$\_$c/ - log t showed a good linear relation up to 10$\^$5/ hr, and the results of the creep work-time relation for p, B and stress intensity values showed good agreement to those of isochronous stress-strain curves (ISSC) presented in ASME BPV NH. The relation can be simply obtained with only several short-term 1% strain data without ISSC which can be obtained by long-term creep data. Particularly, this relation is useful in estimating stress intensity limit for new and emerging class of high-temperature creeping materials.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.5
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• pp.538-546
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• 2008

In this paper, the constitutive equation is developed to analyze the characteristics of strain-induced plasticity in the range of low temperature of 316 stainless steel. The practical usefulness of the developed equations is evaluated by the comparison between experimental and numerical results. For 316 stainless steel, constitutive equations, which represent the characteristics of nonlinear material behavior under the cryogenic temperature environment, are developed using the Bodner's plasticity model. In order to predict the material behaviour such as damage accumulation, Bodner-Chan's damage model is implemented to the developed constitutive equations. Based on the developed constitutive equations, 3-D finite element analysis program is developed, and verified using experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.11
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• pp.1856-1863
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• 2003

Overlay model had several advantages to describe hysteretic behavior of material and showed good capability for many engineering materials. However, this model is only applicable to material obeying Masing postulate. Some materials such as 316L stainless steel do not follow Masing postulate and show cyclic hardening(or softening) and strain range dependence. Low cycle fatigue tests of 316L stainless steel at 600$^{\circ}C$ were performed to investigate the characteristics of cyclic behavior of non-Masing material. From all tests cyclic softening was observed. There were differences in elastic limit of hysteresis loop according to applied strain range. To consider these features, modified overlay model was developed. Yield stresses of subelements were divided into isotropic and anisotropic part to describe the non-Masing behavior. The plastic strain range memorization was introduced to consider the strain range dependence. The prediction using modified overlay model showed a good accordance to actual hysteresis loops.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2211-2219
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• 2000

Near net shape forming of 316L stainless steel powder was investigated under hot isostatic pressing. To simulate densification and deformation of a powder compact in a container during hot isostatic pressing, the constitutive model of Abouaf and co-workers was implemented into a finite element analysis. An optimal design technique based on the design sensitivity was applied to the container design during hot isostatic pressing. The optimal shape of the container was predicted from the desired final shape of a powder compact by iterative calculations. Experimental data of 316L stainless steel powder showed that the optimally designed container allowed precise forming of the desired powder compact during hot isostatic pressing.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.18 no.1
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• pp.26-35
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• 2022

When piping system in a nuclear power plant is subjected to a beyond design seismic condition, it is important to accurately determine possibility of crack initiation and, if initiation occurs, its location and time. From recent experimental works on elbow pipes, it was found that the crack initiation location and crack propagation direction of the SA403 WP316 stainless steel elbow pipe were affected by the pipe thickness. In this paper, the crack initiation location and crack propagation direction for SA403 WP316 stainless steel elbow pipes with different thickness were analyzed via elastic-plastic finite element analysis. Based on FE results, the effect of the pipe thickness on different crack initiation location and crack propagation direction was analyzed using ovality, stress and strain components. It was also confirmed that the presence of internal pressure had no effect on the crack initiation location and crack propagation direction.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.241-247
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• 2014

This study presents the ultrasonic nonlinearity of AISI316 austenitic stainless steels subjected to longterm isothermal aging. These steels are attractive materials for use in industrial mechanical structures because of their strength at high-temperatures and their chemical stability. The test materials were subjected to accelerated heat-treatment in an electrical furnace for a predetermined aging duration. The variations in the ultrasonic nonlinearity and microstructural damage were carefully evaluated through observation of the microstructure. The ultrasonic nonlinearity stiffly dropped after aging for up to 1000 h and, then, monotonously decreased. The polygonal shape of the initial grain structures changed to circular, especially as the annealing twins in the grains dissolved and disappeared. The delta ferrite on the grain boundaries could not be observed at 1000 h of aging, and these continuously transformed into their sigma phases. Consequently, in the intial aging period, the rapid decrease in the ultrasonic nonlinearity was caused by voids, dislocations, and twin annihilation. The continuous monotonic decrease in the ultrasonic nonlinearity after the first drop resulted from the generation of $Cr_{23}C_6$ precipitates and ${\sigma}$ phases.

• Corrosion Science and Technology
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• v.14 no.6
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• pp.261-266
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• 2015

The capacity of passive metal to repassivate after film damage determines the development of local corrosion and the resistance to corrosion failures. In this work, the repassivation kinetics of 316L stainless steel (316L SS) was investigated in borate buffer solution (pH 9.1) using a novel abrading electrode technique. The repassivation kinetics was analyzed in terms of the current density flowing from freshly bare 316L SS surface as measured by a potentiostatic method. During the early phase of decay (t < 2 s), according to the Avrami kinetics-based film growth model, the transient current was separated into anodic dissolution ($i_{diss}$) and film formation ($i_{film}$) components and analyzed individually. The film reformation rate and thickness were compared according to applied potential. Anodic dissolution initially dominated the repassivation for a short time, and the amount of dissolution increased with increasing applied potential in the passive region. Film growth at higher potentials occurred more rapidly compared to at lower potentials. Increasing the applied potential from 0 $V_{SCE}$ to 0.8 $V_{SCE}$ resulted in a thicker passive film (0.12 to 0.52 nm). If the oxide monolayer covered the entire bare surface (${\theta}=1$), the electric field strength through the thin passive film reached $1.6{\times}10^7V/cm$.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.666-670
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• 2001

To improve the corrosion resistance of separator wet-seal area which is the barrier of commercialization of molten carbonate fuel cell(MCFC), Ni/Y/Al coating layer was fabricated by Ni electroplating and Y, Al e-beam PVD on AISI 316L stainless steel. NiAlY alloy coating layer was formed by heat treatment in reduction atmosphere at $800^{\circ}C$ for 5hr. Immersion test in molten carbonate salt at $650^{\circ}C$ was performed on as- received AISI 316L stainless steel and NiAlY coated specimen. According to cross sectional SEM/EDS observations, corrosion resistance of separator wet-seal area was improved by formation of dense oxide layers of Al and Y.

• Journal of Power System Engineering
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• v.14 no.2
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• pp.71-77
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• 2010

This paper was studied on microstructure, mechanical properties and corrosion characteristics of 316L stainless steel pipe welds was fabricated by orbital welding process. S-Ar specimen was fabricated by using Ar purge gas and S-$N_2$ specimen was fabricated by using $N_2$ purge gas. Ferrite was not detected in weld metal of S-$N_2$ specimen but the order of 0.13 Ferrite number(FN) was detected in weld metal of S-Ar specimen. Oxygen and Nitrogen concentration of S-$N_2$ specimen was higher than S-Ar specimen on HAZ and inner bead. The welds microstructural characteristics of S-Ar and S-$N_2$ specimens are similar. The microvickers hardness values of S-Ar and S-$N_2$ specimens welds were similar and average values of each regions were in the range of 174~194. The microstructures of S-Ar and S-$N_2$ weld metal were full austenite by primary austenite solidification. The Solidification structures of S-Ar and S-$N_2$ weld metal were formed directional dendrite toward bead center. The potentiodynamic polarization curve of STS 316L pipe welds exhibited typical active, passive, transpassive behaviour. Corrosion current density$(I_{corr.})$ and corrosion rate values of S-Ar specimen in 0.1M HCl solution were $0.95{\mu}A/cm^2$ and $0.31{\mu}A$/year respectively. The values of S-$N_2$ specimen were $1.4{\mu}A/cm^2$ and $0.45{\mu}m$/year.