• 열처리공학회지
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• 제35권6호
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• pp.303-313
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• 2022

The purpose of this study was to test and analyze the effects of the mechanical properties and structural changes of the austenitized and tempered martensite STS 410 stainless steel containing 11.5~13%Cr and 0.10%C on its temper embrittlement. The STS 410 stainless steel test pieces for each 3 hours at 960℃, 1000℃ and then, tempered them for 2 hours at 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃ and 700℃ known as the intervals vulnerable to temper embrittlement to observe the changes of their structures and mechanical properties. In case autenitizing was insufficient due to lower temperature of thermal treatment for solution, unsolved carbides and ferrites remained in the structure after quenching, which meant that the parts could wear out and corrode to embrittle at the room temperature. Elongation and impact energy changes with Tempering conditions showed minimum results in range of 400~500℃. The decrease in elongation and impact energy at 400~500℃ was the hardening effect of the subgrain due to the precipitation of many M₃C or M₇C₃, M₂₃C₆. And STS 410 stainless steel corrosion tested in 10% NaCl solution at 30℃ after tempering treatment. The degree of corrosion sensitization showed increasing tendency with increase of tempering temperature and Cr carbide precipitation were observed in grain boundary.

• Journal of Welding and Joining
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• 제5권1호
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• pp.34-41
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• 1987

To explore the possible application of thermal analysis technique as a probe for finding weld defects, Hydrogen trapping phenomena in Heat Affected Zone (HAZ) of the AISI 5160 spring steel were investigated. HAZ was divided into five parts, which were used as thermal analysis specimens. Two types of trap sites were found in HAZ, ferrite/cementin interface and microvoid. The thermal analysis peak due to the ferrite/cementite interface increased its height toward the weld deposit. The thermal analysis peak due to the microvoid was the highest where the grain size was the smallest. The correspondence between the cold cracking and hydrogen trap nature is also discussed.

• Nuclear Engineering and Technology
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• 제29권5호
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• pp.361-367
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• 1997

The phase separation in ferrite phase of duplex stainless steel is the primary cause of thermal aging embrittlement of the LWR primary pressure boundary components. In this study the phase separation of simulated duplex stainless steel was detected by Mossbauer spectroscopy and magnetic property analysis by VSM(Vibrating Specimen Magnetometer). The simulated duplex stainless steels, Fe-Cr binary, Fe-Cr-Ni ternary, and Fe-Cr-Ni-Si quarternary allots, were aged at 370 and 40$0^{\circ}C$ up to 5,340 hours. It was observed from Mossbauer spectra analysis that internal magnetic field increases with aging time and from VSM that the specific saturation magnetization and Curie temperature increase with aging time. These result are indicative that phase separation into Fe-rich region and Cr-rich region is caused by thermal aging in the temperature range of 370~40$0^{\circ}C$ In cases of specimens containing Ni, the increase of specific saturation magnetization is much higher. This implies that Ni seems to promote Fe-Cr interdiffusion, which accelerates the phase separation into Fe-rich $\alpha$ phase and Cr-rich $\alpha$' phase.

• Journal of Mechanical Science and Technology
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• 제15권1호
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• pp.26-34
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• 2001

Most research to date concerning the cryogenic toughness of austenitic stainless steels has concentrated on the base metal and weld metal in weldments. The most severe problem faced on the conventional austenitic stainless steel is the thermal aging degradation such as sensitization and carbide induced embrittlement. In this paper, we investigate the cryogenic toughness degradation which can be occurred for austenitic stainless in welding. The test materials are austenitic stainless JN1, JJ1 and JK2 steels, which are materials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch(SP) test was conducted to detect similar isothermally aging condition with material degradation occurred in service welding. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless steels. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.

• 대한기계학회논문집A
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• 제30권12호
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• pp.1526-1533
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• 2006

The aim of this research was to confirm the existence of the thermal creep degradation by hydrides of Zr-2.5Nb pressure tube materials. Small punch creep tests were performed to obtain the relationship between a creep displacement and a loading period at $300^{\circ}C$. A creep stress and a creep strain rate were also converted from the previous results. The creep material constants and the creep stress exponents at the different hydride contents were compared. Finally the hydrides of the axial and circumferential section were observed using OM, SEM and TEM. The following conclusions were made: 1) The degradation of the thermal creep by hydrides was existed and it strongly depended on the hydride contents. 2) As the hydride contents were increased, the creep stress exponents (m) were also increased. 3) Even though the hydride was not precipitated in 50 ppm materials at $300^{\circ}C$, the degradation of thermal creep was found. Therefore, it was believed that this phenomenon strongly related to the hydride precipitation at room temperature.

• Design & Manufacturing
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• 제16권2호
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• pp.46-52
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• 2022

As the consumer market in the eco-friendly vehicle industry grows, the demand for water pump in a electric car parts market. This study intend to propose a mathematical model that can verify the effect of improving thermal properties when a non-conductive cooling filler liquid is introduced into an electric vehicle water pump. Also, the pros and cons of the immersion cooling method and future development way were suggested by analyzing the cooling characteristics using on the derived analysis solution. Thermal characteristics analysis of electric water pump applied with non-conductive filler liquid was carried out, and the diffusion boundary condition in the motor body and the boundary condition the inside pump were expressed as a geometric model. As a result of analyzing the temperature change for the heat source of the natural convection method and the heat conduction method, the natural convection method has difficulty in dissipating heat because no decrease in temperature due to heat release was found even after 300 sec. Also, it can be seen that the heat dissipation effect was obtained even though the non-conductive filling liquid was applied at the 120 sec and 180 sec in the heat conduction method. It has proposed to minimize thermal embrittlement and lower motor torque by injecting a non-conductive filler liquid into the motor body and designing a partition wall thickness of 2.5 mm or less.

• Nuclear Engineering and Technology
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• 제30권6호
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• pp.609-616
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• 1998

Cast duplex stainless steels are extensively used for primary pressure boundary components. These components are, however, embrittled due to the precipitation of $\alpha$' phase by spinodal decomposition and other processes when exposed to reactor operating temperature for a design lifetime or life extension conditions. This report presents a procedure for estimating the current condition and the residual life of safety-related stainless steel components by using ANL database and correlations. The database of Charpy impact energy suggests that CF-8M grade is the most susceptible to thermal aging and CF-3 grade is the least. Thus, the integrity of CF-8M alleys may be degraded seriously and the degree of deterioration may exceed acceptance limit after several years of service in the nuclear reactors.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.377-379
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• 2005

This study has been conducted to clarify the effect of sulfur content and welding thermal cycles on reheat cracking susceptibility in the multi-pass weld metal of Fe-36%Ni alloy. Reheat cracking occurred in the preceding weld pass reheated by subsequent passes. Microscopic observations showed that reheat cracking propagated along grain boundaries which resulted in intergranular brittle fractures. The region where reheat cracking occurred and the number of cracks increased with the increase in sulfur content of the alloys. These experimental results suggested that reheat cracking was associated with the embrittlement of grain boundaries, which was promoted by sulfur and subsequent welding thermal cycles. AES analysis indicated that the sulfur segregation occurred at grain boundaries in the reheated weld metal. On the basis of these results, the cause of reheat cracking in multi-pass welding can be attributed to hot ductility loss of weld metals due to sulfur segregation which was accelerated by the reheating with multi-pass welding thermal cycles.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.286-291
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• 2000

The reactor pressure vessel is usually cladded with stainless steel to prevent corrosion and radiation embrittlement, and number of subclad cracks have been found during an in-service-inspection. Therefore assessment for subclad cracks should be made for normal operating conditions and faulted conditions such as PTS. Thus, in order to find the optimum fracture assessment procedures for subclad cracks under a pressurized thermal shock condition, in this paper, three different analyses were performed, ASME Sec. XI code analysis, an LEFM(Liner elastic fracture mechanics) analysis and an EPFM(Elastic plastic fracture mechanics) analysis. The stress intensity factor and the Maximum $RT_{NDT}$ were used for characterizing. Analysis based on ASME Sec. XI code does not completely consider the actual stress distribution of the crack surface, so the resulting Maximum allowable $RT_{NDTS}$ can be non-conservative, especially for deep cracks. LEFM analysis, which does not consider elastic-plastic behavior of the clad material, is much more non-conservative than EPFM analysis. Therefore, It is necessary to perform EPFM analysis for the assessment of subclad cracks under PTS.

• 대한기계학회논문집A
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• 제25권2호
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• pp.275-282
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• 2001

The reactor pressure vessel is usually cladded with stainless steel to prevent corrosion and radiation embrittlement. Number of subclad cracks may be found during an in-service-inspection due to the presence of cladding. It is specified, in ASME Sec. XI, that a subclad crack is characterized as a surface crack when the thickness of the clad is less than 40% of the crack depth. This condition is provided to keep the crack integrity evaluation conservative. In order to refine the fracture assessment procedures for such subclad cracks under a pressurized thermal shock condition, three dimensional finite element analyses are applied for various subclad cracks existing under cladding. A total of 36 crack geometries are analyzed, and the results are compared with those for surface cracks. The resulting stress intensity factors for subclad cracks are 6 to 44% less than those for surface cracks. It is proven that the flaw characterization condition as specified in ASME Sec. XI can be overly conservative for some subclad cracks.