• Journal of Welding and Joining
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• v.2 no.1
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• pp.4-17
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• 1984

Overlaid weld metals of austenitic stainless steel in a pressure vessel of power reactor are usually post-weld heated for a long period of time after welding. The PWHT is considered as a kind of sensitizing and it is important to check the soundness of the weld metal after PWHT, especially about the precipitation of carbides. The purpose of this report is to obtain information on the relation between the change of microstructure and Post-Weld Heat Treatment in the overlaid weld metals. Metallurgical aspects of the problem on austenitic stainless steel heated at $625^{\circ}C$, $670^{\circ}C$, $720^{\circ}C$ and $760^{\circ}C$ for 3, 10, 30, 100 and 300 hours have been investigated by means of optical-micrography, micro-hardness measurement, scanning electron microscope and electron-probe micro analysis. From the results obtained, the following conclusions are drawn; 1) The PWHT above $625^{\circ}C$ for a long time causes a diffusion of carbon atoms from low alloy steel into stainless steel, and consequently carbon is highly concentrated at the boundary layer of stainless steel. 2) C in ferritic steel migrated to austenitic steel and carbides precipitated in austenitic steel along fusion line. At higher temperatures, the ferrite grains coarsened in the decarburized zone. 3) In the change of microstructure of stainless steel overlaid weld metal, the width of carbides precipitated zone and decarburized zone increased with increase of PWHT temperature and time. 4) At about $625^{\circ}C$ to $760^{\circ}C$, chromium carbides, mainly $M_{23} C_6$, precipitate very closely in the carburized layer with remarkable hardening. 5) Precipitation of delta ferrite from molten weld metal depends on solidification phenomenon. There was a small of ferrite near the bond in which the local solidification time was short, comparing with after parts of weld metal. Shape and amount of ferrite were not changed by Post-Weld Heat Treatment after solidification.

• Journal of the Korean Society for Nondestructive Testing
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• v.9 no.1
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• pp.8-21
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• 1989

This paper presents the ultrasonic characteristics of weldment and detectability of defects of weldment in Austenitic Stainless Steel Type 304 that is composed of mostly coolant piping system in nuclear power plants. The results of this experient show as follows: 1. When the ultrasonic beam detects the defects on the side of base metal and on the opposite side of weldment, the indications which was detected on the screen show different amplitude and different metal path each. 2. The ultrasonically estimated notch depth is generally oversized than actual notch depth. 3. It is easy for the false indication to show up on the screen because of columnar structure of weldment in austenitic stainless steel. 4. The higher frequencies of transducer have more difficulties to detect the defects of the opposite side of weldment because of ultrasonic attenuation in weldment and the longitudinal transmitter-receiver transducer is the most effective in detecting the opposite side defects of weldment.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.118-123
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• 2004

Cast austenitic stainless steel have been widely used for primary coolant piping in light water reactors. This material is subject to thermal embrittlement at reactor operating temperature. CF-8M and CF-8A cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing, and valve bodies in light water reactors. Thermal embrittlement results in spinodal decomposition of delta-ferrite leading to decreased fracture toughness. In this study, the specimens were prepared using an accelerated aging method. The measurement of ferrite content, Charpy impact test and J-R test were performed to verify the predicting equation for aged material properties. In case of above 25% ferrite content, predicted result of J-R curve might be non-conservative.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.131-136
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• 2003

CF8M cast austenitic stainless steel is used for several components such as primary coolant piping, elbow, pump casing, and valve bodies in light water reactors. These components are subject to thermal aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the delta-ferrite leading to increased strength and decreased toughness. In this study, three kinds of the aged CF8M specimen were prepared using an artificially simulated aging method. The objective of this study is to summarize the method of estimating ferrite contents, Charpy impact energy and J-R curve, and to evaluate the thermal embrittlement of the CF8M cast austenitic stainless steel piping used in the domestic nuclear power plants.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.236-239
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• 2000

It is important to evaluate austenitic heat resistant stainless steel because of low weldability of austenitic heat resistant stainless steel containing high Si. This study took varestraint test for evaluation of solidification cracking sensitivity and Erichsen test for evaluation of weld metal ductility. As a result of tests, solidification crack sensitivity increased with adding $N_2$ to shielding gas, and W had detrimental effect on crack resistance, but Ce had beneficial effect on crack resistance. Under same heat input, ductility of weld metal increased with welding speed.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.96-101
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• 2004

Cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing and valve bodies in light water reactors. These components are subject to thermal embrittlement at the reactor operating temperature. The objective of this study is to summarize the method of estimating ferrite content, Charpy impact energy and J-R curve and to evaluate the thermal embrittlement of the cast austenitic stainless steel piping used in the domestic nuclear power plants. The result of evaluation, two domestic nuclear power plants used CF-8M and CF-8A material has adequate fracture toughness after saturation.

• Steel and Composite Structures
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• v.47 no.1
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• pp.135-145
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• 2023

This study presents a numerical investigation into the hysteretic behavior of cold-formed austenitic stainless steel square hollow section (SHS) brace members using a commercial finite element (FE) analysis software ABAQUS/Standard. The initial/post buckling and fracture life of SHS brace members are comprehensively investigated through parametric studies with FE models incorporating ductile fracture model, which is validated against the existing laboratory test results collected from the literature. It is found that the current predictive models are applicable for the initial buckling strengths of SHS brace members under cyclic loading, while result in significant inaccuracy in predictions for the post-buckling strength and fracture life. The modified predictive model is therefore proposed and the applicability was then confirmed through excellent comparisons with test results for cold-formed austenitic stainless SHS brace members.

• Proceedings of the KWS Conference
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• 2001.05a
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• pp.248-251
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• 2001

• Journal of Korea Foundry Society
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• v.21 no.5
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• pp.280-285
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• 2001

Nb-containing austenitic stainless steel is widely used as exhaust frame and diffuser assembly in power plant. However, this steel is known to be difficult to produce by the continuous casting process due to the surface cracks. Therefore, the continuous casting technology was developed for the prevention of the surface cracks on CC slabs. Precipitates and the analysis of heat trasfer in a slab were investigated in order to find out the formation mechanism of surface cracks on cc slabs It was found that surface cracks are occurred due to the NbC precipitates, which are formed along the grain boundaries around $800^{\circ}C$. The secondary cooling pattern has been developed to produce the defect free CC slabs of Nb-containing austenitic stainless steel.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.3
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• pp.121-126
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• 2014

High-nitrogen Fe-18Mn-18Cr-N austenitic steels with higher yield strength have been recently developed and used for generator retaining rings because they have non-magnetic, high strength, high ductility, and good corrosion resistance. In the present study, a high-nitrogen Fe-18Mn-18Cr-0.61N austenitic steel was fabricated and then tensile and Charpy impact tests were conducted on them in order to investigate the effect of cold working on the mechanical properties. Although the yield and tensile strengths usually increased with cold working, the ductility and impact toughness significantly decreased after cold working. On the other hand, the high-nitrogen austenitic steel exhibited a ductile-brittle transition due to unusual brittle fracture at low temperatures despite having a face-centered cubic structure. The ductile-brittle transition temperature obtained from Charpy impact tests could be remarkably increased by $60^{\circ}C$ after 20% cold working because of the enhanced cleavage-like brittle fracture.