김승우 교수

This article undertakes an investigation of the stress corrosion crack growth behavior of a cold-rolled Alloy 690 (UNS N06690) with microstructural inhomogeneity in the primary water of a pressurized water reactor, and ascertains the relationship between this behavior and the local distribution of the residual strain. Stress corrosion cracking (SCC) was found to propagate in a transgranular mode through a banded region composed of intragranular carbides and small-sized grains, and in an inter-gr

Measuring the residual stress in the components in nuclear power plants is crucial to their safety evaluation. The instrumented indentation technique is a minimally invasive approach that can be conveniently used to determine the residual stress in structural materials in service. Because the indentation behavior of a structure with residual stresses is closely related to the elastic-plastic behavior of the indented material, an accurate understanding of the elastic-plastic behavior of the mater

A stress–strain curve is one of the most important indicators of material properties for characterizing constitutive behavior. It can be directly obtained from a conventional uniaxial tensile test or load–displacement curve using an instrumented indentation test (IIT). An IIT uses formulations of the effective indentation strain and stress or the iterative finite element analysis (FEA) of the indentation process using a constitutive model, such as a power-law constitutive model. In this study, a

The purpose of this study is to elucidate the effect of plastic deformation on the microstructure and general corrosion behavior of Alloy 690 in a simulated steam generator crevice of a pressurized water reactor secondary system containing hydrogen. As the degree of deformation increased, the surface roughness and surface defects such as ripped surface and micro-cracks increased. Compared with the non-deformed specimen, the dislocation density of the deformed specimen greatly increased and the l

This work aims to establish a model of a primary water stress corrosion crack growth rate of Alloy 690 material for the head penetration nozzles of Korean pressurized water reactors. The test material had an inhomogeneous microstructure with bands of fine-grains and intragranular carbides in the matrix of coarse-grains, which was similar to the archive materials of the head penetration nozzles. The crack growth rate was measured from the strain-hardened materials as a function of the stress inte

In this study, a new rupture disk corrosion test (RDCT) method was developed for real-time detection of stress corrosion cracking (SCC) initiation of Alloy 600 in a primary water environment of pressurized water reactors. In the RDCT method, one side of a disk specimen was exposed to a simulated primary water at high temperature and pressure while the other side was maintained at ambient pressure, inducing a dome-shaped deformation and tensile stress on the specimen. When SCC occurs in the prima

A significant process for highly precise measurement in 2-D inspection and 3D surface metrology is accurate and consistent imaging of target being measured. Dithering locking method, one of widely-used focus-locking method, has been only applied to objective modulation type which cause physical influence and image distortion. To overcome this, we have developed an actively locked focus-tracking system based around source dithering technique using fiber-optic confocal principle. Further, the whol

The object of this work is to establish an electrochemical noise(EN) measurement technique combined with a direct current potential drop(DCPD) method for monitoring of localized corrosion cracking of nickel-based alloy, and to analyze its mechanism. The electrochemical current and potential noises were measured under various conditions of applied stress to a compact tension specimen in a simulated primary water chemistry of a pressurized water reactor. The amplitude and frequency of the EN signa

The dislocation density in strain-hardened Alloy 690 was analyzed using scanning transmission electron microscopy (STEM) to study the relationship between the local plastic strain and susceptibility to primary water stress corrosion cracking (PWSCC) in nuclear power plants. The test material was cold-rolled at various thickness reduction ratios from 10% to 40% to simulate the strain-hardening condition of plant components. The dislocation densities were measured at grain boundaries (GB) and in g

The early-stage M23C6 morphology at the phase boundary between austenite and δ ferrite grain in Type 304L austenitic stainless steel was investigated with transmission electron microscopy (TEM). The M23C6 has coherency with austenite grains at phase boundary. The phase boundary between the M23C6 and austenite grains has curved appearance. The curved phase boundary might be a faceted interface composed of (111) plane and the other low-index planes on the atomic scale. The M23C6 morphology at the

This paper describes a three-probe system that can be used to measure the parallelism and straightness of a pair of rails simultaneously. The parallelism is measured using a modified reversal method, while the straightness is measured using a sequential two-point method. The measurement algorithms were analyzed numerically using a pair of functionally defined rails to validate the three-probe system. Tests were also performed on a pair of straightedge rails with a length of 250 mm and a maximum

Rupture disk corrosion test (RDCT) method has been recently developed for real-time measurement of initiation of stress corrosion cracking (SCC) in a high-temperature water. This work presents a parametric study on the stress distribution of a thin disk specimen of RDCT to consider the fixture shape and friction using finite element analysis (FEA). The FEA results showed a dome-shaped deformation of the specimen. From the stress analysis as a function of friction coefficient, it was suggested th