• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.92-97
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• 1996

The fatigue crack propagation behavior in SA106 Gr.C main steam pipe weld joint was investigated in air environment. Crack growth rate tests were conducted on base metal and weld metal at load ratio of 0.1 and 0.3 and at frequency of 10Hz. The fatigue crack growth rates of the base metal and the weld metal were above the ASME reference line and the fatigue crack propagation rate of the weld metal was higher than those of the base metal. Fatigue crack growth rate increased with increasing the load ratio and the effect of the load ratio was more significant in the weld metal. The post weld heat treatment increased the fatigue crack growth rates of the base metal by reducing compressive residual stress and decreased those of the weld metal by reducing weld defects.

• Proceedings of the KWS Conference
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• v.43
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• pp.272-274
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• 2004

• Journal of Welding and Joining
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• v.14 no.3
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• pp.75-85
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• 1996

In this paper the influence of postweld heat treatment on mechanical properties of SMAW and FCAW stainless steel weldments was examined and the obtained results are as follows ; (1) The amount of $\delta$-ferrite formed by SMAW and FCAW process decreased with increasing holding temperature and time in post weld heat treatment(PWHT), and it was found that the reduced ferrite was transformed into sigma phase after $800^{circ}C{\times}50hr$ PWHT. This sigma phase, even though it was very small, resulted in brittleness of dissimilar weldment between carbon steel and stainless steel in bending test, however in similar weldment between stainless steel and stainless steel was not occured. (2) The chemical composition of sigma phase was measured to 28-30%Cr, 7-9%Mo, 4-6Ni in 316L weldment, and also 35-37%Cr, 0.9-1.0Mo, 6-8%Ni in 309L weldment by EDS analysis.

• Journal of Welding and Joining
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• v.35 no.1
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• pp.26-33
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• 2017

This study aims to investigate the suitability of requirement for post-weld heat treatment(PWHT) temperature when different P-No. materials are welded, which is defined by ASME Sec. III Code. For SA-516 Gr. 60 and SA-106 Gr. B carbon steels that are typical P-No. 1 material, simulated heat treatment were conducted for 8 h at $610^{\circ}C$, $650^{\circ}C$, $690^{\circ}C$, and $730^{\circ}C$, last two temperature falls in the temperature of PWHT for P-No. 5A low-alloy steels. Tensile and Charpy impact tests were performed for the heat-treated specimens, and then microstructure was analyzed by optical microscopy and scanning electron microscopy with energy-dispersive spectrometry. The Charpy impact properties deteriorated significantly mainly due to a large amount of cementite precipitation when the temperature of simulated heat treatment was $730^{\circ}C$. Therefore, when dissimilar metal welding is carried out for P-No. 1 carbon steel and different P-No. low alloy steel, the PWHT temperature should be carefully selected to avoid significant deterioration of impact properties for P-No. 1 carbon steel.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.252-254
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• 2004

Fatigue life a box weldment was predicted with the stress concentration and residual stress using the equation reported. In order to change the stress concentration and residual stress of the box weldment, Post treatments such as smooth grinding of weld bead, weld toe grinding and hammer peening were applied. The fatigue life of the weldment after post treatment clearly increased, which is attributed to the reduction of stress concentration and/or introduction of compressive residual stress at the weld toe. The predicted fatigue life was a relatively good agreement with the experiment for a long fatigue life, while it was underestimated for a short fatigue life.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.132-137
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• 2008

A failure analysis of ammonia converter which suffered hydrogen attack in two years since its initial operating time was presented. It is constructed from 2.25 Cr.1 Mo steel. Analysis showed that the failure on closing seam weld joint was due to local improper post weld heat treatment (PWHT). Improper PWHT can introduce high residual stresses in thick-walled pressure vessel. High residual stress level in weld joint is very prone to hydrogen attack for any components which are operating in hydrogen gas environment. The repair procedures based on the principle to decrease the residual stress then proposed. The repair was controlled very carefully by applying several nondestructive tests in the each stage of repair. To assure the successful of the proposed repair, after one year since repair time, high temperature ultrasonic and TOFD methods were applied on-stream to this equipment in order to evaluate its post repair condition. The two methods showed good results on the repaired area.

• Journal of Power System Engineering
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• v.10 no.1
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• pp.77-82
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• 2006

In this study, dissimilar friction welding were produced using 15mm diameter solid bar in chrome molybedenum steel(SCM440) to carbon steel(S45C) to investigate their mechanical properties and the relationship between the weld parameters and the nondestructive coefficients, such as AE counts and ultrasonic attenuation coefficient. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond of area and heat affected zone. The specimens were tested as-welded and post weld heat treated(PWHT). The tensile strength of the friction welded steel bars was increased up to 100％ of the S45C base metal under the condition of all heating time. The ductility of PWHT specimens is higher than as-welded.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.48-55
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• 2013

In this study, fatigue tests were performed on longitudinal out-of-plane gusset fillet welded joints and transverse non-load-carrying cruciform rib fillet welded joints, and then applicability of hammer-peening treatment on improvement of fatigue life for fatigue damaged weld joints were investigated. Fatigue tests were carried out on three types of gusset and rib welded specimens: as-welded specimens, post-weld hammer peened specimens and hammer peened specimens at 50% of as-welded specimen's fatigue life. Before and after hammer peening treatment, the geometry of weld toes and surface stresses near weld toes were measured. As a result of hammer peening treatment, compressive residual stresses of 30-83MPa were introduced near weld toes of the gusset and rib welded joints, and 130% increase in fatigue life and fatigue limit of the welded joints could be realized by hammer peening treatment at 50% fatigue life of as-welded conditions.

• Corrosion Science and Technology
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• v.16 no.6
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• pp.278-284
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• 2017

The effects of TIG welding and post-treatment procedures on the microstructure and the pitting corrosion resistance of welded lean duplex stainless steel S82441 were investigated. Autogenous TIG welding was used with different amounts of heat input and shielding gases such as Ar, and mixtures of $Ar-N_2$ and Ar-He. The addition of 5% to 15% of nitrogen to argon practically did not affect the level of the pitting corrosion resistance. However, the application of gas mixtures (50% Ar + 50% He) resulted in a significant decrease in pitting corrosion resistance. We found that increased current (200 A and 250 A) led to lower values of CPT of welds compared with welds obtained with 50 A, 100 A and 150 A. In addition, the removal of the weld surface layer (0.2 ~ 0.3 mm thickness) in most cases not only resulted in a significant increase in resistance to the pitting corrosion but also post-treatment of weld, implying that corrosion resistance depended on factors such as surface roughness or the presence of undesirable oxides.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.5
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• pp.517-523
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• 2021

In this study, in the selection of materials for the elements of a small plant, those with high resistance to corrosion are selected and the material properties of coatings for corrosion prevention are evaluated. In addition, corrosion characteristics and material analysis were performed on the welded part, and the hardness characteristics of the welded part, heat-affected part, and the base metal were evaluated. In the case of the post-weld-heat-treated(PWHT) specimen, the corrosion resistance of STS 316 was lower than that of the specimen without the PWHT due to the formation of intergranular carbide. As a result of evaluating the distribution of the hardness of the weld before and after the PWHT, the hardness of the specimen after the PWHT increased by about 20 Hv. As a result of the corrosion test on the welded specimen, the weight loss tended to increase as the time increased. In the case of the PWHT specimen, the corrosion resistance tended to be significantly lower than that of the specimen without PWHT due to the formation of intergranular carbide.