• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.9 s.240
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• pp.1253-1261
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• 2005

Cast stainless steel (CSS) is thermally aged by a long term exposure in the range of nuclear power plant operating temperature. The thermal aging is a cause of concern for the continued safe and reliable operation of CSS nuclear components. Therefore, an assessment of degradation in material properties of these components has been importantly considered. In this study the ball indentation tests were performed on four cast stainless steels aged at $400^{\circ}C$ for 3600 hours, to investigate the applicability of ball indentation test to the assessment of aging degradation of cast stainless steels. Thus, the reliability of ball indentation test for aged CSS was analyzed by evaluating the scattering of data tested from each material and by comparing tensile properties obtained from ball indentation test and standard tensile test. Also, the tensile properties of aged CSS obtained from ball indentation test were compared with those predicted by the evaluation procedure developed on the basis of material database for aged CSS.

• Journal of Welding and Joining
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• v.22 no.1
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• pp.77-82
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• 2004

The effect of bonding condition on tensile properties of joints diffusion bonded spheroidal graphite cast iron, FCD60 to Cr-Mo steel, SCM 440 was investigated. Diffusion bonding was performed with various temperatures, holding times, pressures and atmospheres. All tensile specimens were fractured at the bonding interface. The tensile strength and elongation was increased with increasing bonding temperature. Especially, tensile strength of joints bonded at 1123K was higher than that of a raw material, FCD60, and tensile strength of joints bonded at 1173K was equal to that of a raw material, SCM440, but elongation of all joints was lower than those of raw materials. There was little the effect of holding time on the tensile properties. In comparison with bonding atmosphere, the difference of tensile strength was not observed, but elongation of joint bonded at vacuum(6.7mPa and 67mPa) was higher than that of Ar gas. Higher the degee of vacuum, elongation increased. Tensile properties of diffusion bonds depended on microstructures of cast iron at the interface and void ratio. Microstructures of cast iron at interface changed with temperature, because decarburizing and interdiffusion at the interface occurs and transformation of austenite-1 ferrite + graphite occurs on the cooling process. The void ratio decreased with increasing temperature, especially, effected on the elongation.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.1
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• pp.29-36
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• 2010

Ultrasonic inspection of heavy walled cast austenitic stainless steel(CASS)welds is very difficult due to complex and coarse grained structure of CASS material. The large size of anisotropic grain strongly affects the propagation of ultrasound by severe attenuation, change in velocity, and scattering of ultrasonic energy. therefore, the signal patterns originated from flaws can be difficult to distinguish from scattered signals. To improve detection and sizing capability of ID connected defect for heavy walled CASS piping welds, the low frequency segmented TRL Pulse Echo and Phased Array probe has been developed. The experimental studies have been performed using CASS pipe mock-up block containing artificial reflectors(ID connected EDM notch). The automatic pulse echo and phase array technique is applied the detection and the length sizing of the ID connected artificial reflectors and the results for detection and sizing has been compared respectively. The goal of this study is to assess a newly developed ultrasonic probe to improve the detection ability and the sizing of the crack in coarse-grained CASS components.

• Journal of Korea Foundry Society
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• v.38 no.1
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• pp.16-26
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• 2018

In this study, the effects of the pouring temperature, preheating temperature, surface condition and fraction of the wear resistant part on the production of duo-castings were investigated using a high Cr white cast iron with excellent abrasion resistance and a low Cr alloy steel with good toughness. The constituent materials of the duo-castings were designed to have high hardness, fracture toughness and abrasive wear resistance for the replacement of high Mn alloy steels with low abrasive wear resistance. In particular, the amount of abrasive wear of 17% Cr white cast iron was about 1/20 of that of high Mn alloy steel. There was an intermediate area of about 3mm due to local melting at the bonding interface of the duo-castings. These intermediate regions were different from those of the constituent materials in chemical composition and microstructure. This region led to fracture within the wear resistant part rather than at the bonding interface in the bending strength test. The bending fracture strengths were 516-824 MPa, which were equivalent to the bending proof strength of high Mn steel. The effects of various casting conditions on the duo-cast behavior were studied by simple pouring of low Cr alloy steel melt, but the results proved practically impossible to manufacture duo-castings with a sound bonding interface. However, the external heating method was suitable for the production of duo-castings with a sound bonding interface.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.7
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• pp.90-96
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• 2019

Recently, friction stir welding of dissimilar materials are one of the biggest issues in terms of light-weight and eco-friendly technology of the automotive, aircraft and ship industry. In this study, friction stir welding of dissimilar materials is introduced with different tool rotational speed. Materials used in experimentation consist of A357 gravity cast aluminum alloy and FB590 high-strength steel plates. Dissimilar materials of plate type are fabricated with width of 150mm, length of 300mm and thickness of 3mm and welding is carried out by the lap joint method. The correlation between probe length and mechanical properties were investigated according to rotational speed and welding speed at tool tilt angle 0 degree. Consequently, feasibility of FSWed dissimilar materials were successfully presented in case of cast aluminum and high-strength steel at lap joint method.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.3
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• pp.284-291
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• 1999

Recently the ductile cast iron is being used successfully to the parts for processing machinery vessels and gear etc. This study is mainly concerned with the heat treatment for the specimens of crank shaft which are made of ductile cast iron. The results obtained are summarized as follows. Comparing the mechanical properties of the specimens for the normalized ductile cast irons the specimen heat treated at $550^{\circ}C$ was the best for crank shaft of air-compressor. After austenizing at $910^{\circ}C$ it was observed that the higher the reheating temperature is the less tensile strength and the hardness became which was supposedly attributed to the fact that the amount of pearlite. Austenite matrix was reduced by reheating after normalizing and that as the reheating tem-perature went up the pearlite generated was less and the distance between the pearlites were widened at last made pearlite globular. In the comparsison of crank shaft for air compressor made of ductile cast iron with that made by forged steel the crank shaft made of ductile cast iron was superior in economical terms. And ductile cast iron could be practically enough if only the elonga-tion which was inferior mechanical property to forged steel could be reinforced by increasing the diameter of crank pin when designing the crank shaft.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1174-1179
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• 2003

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. This study shows that ferrite content can be predicted by use of the artificial neural network. The neural network has trained learning data of chemical components and ferrite contents using backpropagation learning process. The predicted results of the ferrite content using trained neural network are in good agreement with experimental ones.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.504-509
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• 2017

In order to improve corrosion resistance for cast stainless steel in seawater, the characteristics of corrosion resistance after plasma ion nitriding was investigated. Plasma ion nitriding process was conducted in a mixture of nitrogen of 25% and hydrogen of 75% at substrate temperature ranging from 350 to $500^{\circ}C$ for 10 hours using pulsed-DC glow discharge plasma with working pressure of 250 Pa in vacuum condition. Corrosion tests were carried out for as-received and plasma ion nitrided specimens. The corrosion characteristics were investigated by measurement of weight loss and observation of surface morphology. In anodic polarization experiment, relatively less damage depth and weight loss were presented at a nitrided temperature of $400^{\circ}C$, attributing to the formation of S-phase.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.4
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• pp.460-466
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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 aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the delta-ferrite leading to increased strength and decreased toughness. This study shows that ferrite content can be predicted by use of the artificial neural network. The neural network has trained teaming data of chemical components and ferrite contents using backpropagation learning process. The predicted results of the ferrite content using trained neural network are in good agreement with experimental ones.

• Journal of Welding and Joining
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• v.32 no.5
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• pp.65-71
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• 2014

Atmospheric plasma spraying (APS) is world-widely used process in the automotive industry as a method to provide wear resistance coatings for engine cylinder bore, using various materials. The weight of engine blocks can be considerably decreased by removing cast iron liners, which can finally result in the improvement of fuel efficiency. In this study, five kinds of powder materials, 1.2C steel powder and 1.2C steel powder mixed with 5, 10, 15, 20 wt.%. molybdenum powder, were deposited by atmospheric plasma spraying in order to investigate the effect of molybdenum on the wear resistance of coatings. Microstructural analysis showed that molybdenum splats were well distributed in 1.2C steel matrix with intimate bonding. The molybdenum added coatings showed better tribological properties than 1.2C steel coating. However, above the 15 wt.%. blending fraction, wear resistance was somewhat degraded with poor roughness of worn surface due to the brittle fracture occurred in molybdenum splats. Consequently, compared to conventional liner material, gray cast iron, 10 wt. pct. molybdenum blended 1.2C steel coating showed much better tribological properties and therefore it looks very feasible to replace gray cast iron liner.