• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.541-548
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• 2009

In this study, Charpy impact test and numerical studies were performed to examine the effects of failure behavior and energy absorption on the notch position. For this purpose, carbon steel plate(SA-516 Gr. 70) with thickness of 25mm usually used for pressure vessel was welded by SMAW(Shielded Metal-Arc Welding)method and specimens were fabricated from the welded plate. The Charpy impact tests were then performed with specimens having different notch positions varying within HAZ. A series of three-dimensional FE analysis which simulates the Charpy test and crack propagation are carried out as well. We divided HAZ into two, three and four regions to apply mechanical properties of HAZ to FE-analys. Results reveal that the absorbed energies during impact test depend significantly on the notch position. To obtain the results of reliability, HAZ should be divided into at least three regions.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.3
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• pp.1-9
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• 2001

Impact tests are performed on the high strength structural steel that is being developed for the submarine material. Especially, the impact characteristics of this structural steels at low temperatures are investigated by charpy impact testing. Hyperbolic tangent curve fitting method is used to evaluate the LSE(lower shelf energy), USE(upper shelf energy) and DBTT(ductile-brittle transition temperature). Proportional equations between charpy impact energy and lateral expansion are obtained using the test results. Effect of temperature on the fracture appearance is investigated by using SEM.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.483-491
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• 2011

The fabrication of steel structural members always involves welding process such as flux cored arc welding. Therefore, for the application of structural steels to cold regions, it is a prerequisite to clarify the service temperature of the welded joints in order to ensure the structural integrity of the welded parts. In this study, the Charpy impact test was conducted to evaluate the service temperature of structural steel weld. The Charpy impact test is a commercial quality control test for steels and other alloys used in the construction of metallic structures. The test allows the material properties for service conditions to be determined experimentally in a simple manner with a very low cost. Standard V-notch Charpy specimens were prepared and tested under dynamic loading condition. The service temperatures of the weld metal, HAZ (heat affected zone) and base metal were derived by the absorbed energy and the impact test requirements; thus the applicability of the structural steels to cold regions was discussed in detail.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.693-700
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• 2012

In this study, the Charpy impact test along with metallurgical observation was conducted to evaluate low temperature impact toughness of structural steel welds with different welding processes to find out the optimal welding process to guarantee the required impact toughness at low temperatures. The welding processes employed are shield metal arc welding (SMAW) and flux cored arc welding(FCAW), which are commonly used welding methods in construction. The Charpy impact test is a commercial quality control test for steels and other alloys used in the construction of metallic structures. The test allows the material properties for service conditions to be determined experimentally in a simple manner with a very low cost. To investigate the impact toughness at low temperatures of the steel welds, specimens were extracted from the weld metal and the heat affected zone. Standard V-notch Charpy specimens were prepared and tested under dynamic loading condition. The low temperature impact performance was evaluated based on the correlation between the absorbed energy and the microstructure. Analysis of the results showed that the optimal welding process to ensure the higher low temperature impact toughness of the HAZ and the weld metal is SMAW process using the welding consumable for steels targeted to low temperature use.

• Journal of Korean Society of Steel Construction
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• v.30 no.1
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• pp.13-23
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• 2018

The use of a built-up H-beam (BH) that can easily manufacture a section is increasing. This is a basic study on standardization of BH. It confirmed the material properties of SM490 and SM520 steel such as yield strength, tensile strength, elongation, charpy absorbed energy, and else. The six BH specimens were manufactured with single-SAW or tandem-SAW. The welding performance was confirmed by collecting the macroscopic specimen and T-bar tensile specimen form the BH. As a result of the material property test, the properties of SM490 and SM520 which are made in Korea both satisfied the KS. As a result of the welding performance experiment, it is determined that the weld zone of BH has sufficient welding performance. Therefore, they are determined that the SM490 and SM520 steel are a proper material of BH, and the single-SAW and the tandem-SAW show a sufficient welding performance.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.93-96
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• 2003

Laser beam welding process is a relatively new process in comparison with arc welding process, but it is expected to apply widely because of the many advantages, and research and development of that process is being progressed actively for the practical use. the application of this welding process has been restricted due to the high initial investment and the need of precise processing against the material, but cost reduction and thick plate welding in high speed have become practial by recent technological development, and this welding process to not only small parts in automobile, machinery and physicochemical field, but also a large structure and pipe line are being applied. In order to utilize this welding process appropriately to a steel structure, the properties of welding residual stresses and fracture toughness in welded joints are to be investigated for relibilty. On this study, after performing the finite element analysis, thermal and residual stress properties have been examined to the general structural steel (HT50) by laser beam welding. Besides, the property of fracture toughness has been investigated by the Charpy impact test and 3-points bending CTOD test carried out in the range of temperature between $-60^{\circ}C$ and $20^{\circ}C$. From the research results it is revealed that the maximum residual stress appears in the center of plate thickness and the fracture toughness is influenced by strength mis-match.

• Journal of Ocean Engineering and Technology
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• v.21 no.3 s.76
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• pp.71-76
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• 2007

Recently, many industries have been employing the application of laser beam welding, due to the resulting high welding quality, such as smaller width of melting and heat affective zone, smaller welding deformation, and fine grains of weldment, compared to arc welding. However, in order to appropriately utilize this welding process with steel structure, the characteristics of welding residual stresses and fracture toughness in welded joints are to be investigated for reliability. Therefore, in this study, the mechanical properties of weldments by arc and laser welding are investigated using FEM to confirm the weldability of laser welding to the general structural steel (HT50). The Charpy impact test and 3-points bending CTOD test are carried out in the range of temperatures between $-60^{\circ}C\;and\;20^{\circ}C$, in order to understand the effect on the fracture toughness of weldments. From the research results, it has been found that the maximum residual stress appears at the center of plate thickness, and that the fracture toughness is influenced by strength mis-match.

• Journal of the Korean Institute of Gas
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• v.19 no.6
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• pp.62-66
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• 2015

Considering for plants and structure under extreme conditions is required for the successful design, especially temperature and pressure. The ductile-brittle transition temperature (DBTT) for the materials under extreme condition needs to be considered. In this study, A-grade mild steel for the LNG carrier and offshore plant was examined by performing low-temperature Charpy V-notch (CVN) impact tests to investigate DBTT and the fracture toughness. The absorbed energy decreased gradually with the experimental temperature, which showed an upper-shelf energy region, lower shelf energy region, and transition temperature indicating DBTT. In addition, the fracture surface morphologies of the mild steels indicated ductile fractures at the upper-shelf energy level, with wide and large-sized dimples, whereas a brittle fracture surface, where was observed at the lower-shelf energy level, with both large and small cleavage facets. Based on the experimental results, ductile brittle transition temperature was estimated in about $-60^{\circ}C$.

• Korean Journal of Metals and Materials
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• v.48 no.10
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• pp.875-883
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• 2010

This study assessed the Charpy impact properties of the heat-affected zones (HAZs) of API X80 linepipe steels containing complex oxides. Three types of steel were fabricated by adding Mg and $O_2$ to form complex oxides and their microstructures and Charpy impact properties were investigated. The number of complex oxides increased with the amount of excess Mg and $O_2$ that was included in the steels. Simulated HAZs containing a number of oxides showed a high volume fraction of acicular ferrite (AF) because the oxides acted as nucleation sites for AF, thereby leading to an improvement in the Charpy impact properties. According to a correlation study between the heat input, the volume fraction of the AF, and the Charpy impact properties, ductile fractures occurred predominantly when the fraction of the AF was 20% or higher; moreover, the Charpy absorbed energy was excellent at more than 100 J. These findings suggest that the improvement of the Charpy impact properties of the HAZs was associated with the active nucleation of AF in the oxide-containing steel HAZs.