• Proceedings of the KSME Conference
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• 2004.11a
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• pp.353-358
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• 2004

Tracing the study of the burst test of steam generator tube, few studies have been reported to effect of external pressure acting on secondary-side in service condition. In this study the burst tests of Inconel 690TT were conducted in order to evaluate burst strength characteristics under the effect of external pressure. We obtained the result that the burst strength of Inconel 690TT increased when external pressure increased while both total circumferential elongation and uniform burst elongation were not affected. Also, according to the increased of external pressure, the size of the burst opening became smaller and the tear was getting severe.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.10
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• pp.923-928
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• 2014

Elongation rolling process is an intermediate process to make the uniform thickness and uniform surface roughness during producing seamless pipes. The thickness and surface roughness of seamless pipes are generally affected by the distance of rolls and guide shoes, the roll shape, and its cross angle. In this study, finite element analysis for shape forming process is based on the analysis model of elongation rolling mill with guide shoes. This paper shows how the cross angle of the roll, the rolling rpm, and the distance of the guide shoe influence on the outer diameter and the thickness of seamless pipes. The rolling rpm did not give much influence on outer diameter.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.2
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• pp.95-102
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• 1994

Aluminum sheet application to automobile body panels has now become an important objective to meet the requirements of automobile weight reduction. As the Mg content in Al-Mg based alloys increased up to 7.19%, the strength and elongation increased. For instance. Al-7.19Mg alloy had a high strength of 305MPa and a high elongation of 35%. A study was also made to investigate the interrelation between grain size and tensile properties with varying the contents of Mg, Ti and Zr elements and annealing conditions. The yield stress decreased as the grain size increased, which increased the uniform elongation. The strain hardening exponents n increased as the Mg content increased, which depended on the increasing difficulties of the cross slip of dislocation.

• Transactions of Materials Processing
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• v.3 no.3
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• pp.320-334
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• 1994

A set of full size cold rolled steel sheets has been prestrained in the direction of rolling by uniform tensile elongation of 3% and 6%. Then mid-sized tensile specimens were cut from each of the full size sheets at 30, 45, 60 and 90 degrees to the rolling direction. The mid-sized tensile specimens were then prestrained again by uniform tensile elongation by 1%, 2%, 5%, 10% and 15%. finally, miniature tensile specimens were prepared from each of the mid-sized specimens at every 10 degrees to the specimen axis. From the tensile tests on miniature specimens material's hardening behavior under non-proportional loading has been investigated. There are a number of new observations which has not been known to the authors before current work. One of them is continuous reservation of orthoropic symmetry during tensile elongation of mid-sized specimens. Another is continuous rotations of orthotropy axes. Existing theories seem to fail to explain this observations. A new model is proposed in relation to the rotation of orthotropy axes.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.6
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• pp.327-335
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• 2004

Effect of spherodization of cementite on static and dynamic deformation behaviors of SCM415 steels was investigated in this study. Dynamic torsional test was conducted using torsional Kolsky bar with the strain rate of $1.6{\times}10^3/s$. Three type of specimens were used with different spherodization degree of cementite. Dynamic test results were analyzed comparing with static tensile results and microstructural changes. The obtained results are as follows; 1) All the specimens of static and dynamic tests showed a ductile fracture mode of dimple. Specimens of the dynamic test showed adiabatic shear bands on the beneath of fracture surface. 2) In static tensile test, decreased tensile strength and increased uniform and non-uniform elongations appeared as spherodization degree of cementite increased. 3) In dynamic torsional test, decreased shear strength and increased uniform elongation appeared as spherodization degree of cementite increased. 4) Due to the largest uniform elongation, superior cold forgeability at high speed is expected on high spherodization degree of cementite.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.866-872
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• 2000

Superplastic forming processes by characteristic of low flow stress and high elongation have advantages to reducing on production cost and weight because of the product of complex form could be made in one part. However superplastically termed part has a characteristic of non-uniform thickness distribution along forming direction. Especially. since the thickness distribution affects on mechanical properties of product. the uniform thickness is very important. There are two solution procedure of implicit and explicit procedure to analyze the superplastic forming. In this study to analyze the thickness distribution two kinds of commercial programs of DEFORM and PAM-STAMP which implicit and explicit code are used respectly. The results from the two Programs were compared with eath other As a result implicit code were more suitable than explicit code for superplastic forming analysis.

• Journal of the Korean Society for Heat Treatment
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• v.20 no.1
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• pp.22-30
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• 2007

Effects of ferrite grain size on static and dynamic deformation behaviors of SCM415 stels were investigated in this study. Dynamic torsional test was conducted using torsional Kolsky bar with the strain rate of $1.6{\times}10^3/s$. Specimens with three different grain size of ferrite, $4.6{\mu}m$, $11{\mu}m$, $35.5{\mu}m$ were used. Dimple fracture mode of the dynamic test specimens showed adiabatic shear bands on the beneath of fracture surface. Increased uniform elongation and decreased non-uniform elongation appeared as grain size of ferrite decreased in dynamic torsional test. However, shear strength was independent on grain size of ferrite.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.811-818
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• 2020

Y-containing CLAM steels were melted via vacuum induction melting and electroslag remelting. In this study, the evolution, microstructure, and mechanical properties of the alloy inclusions (ESR-1 (0 wt.% Y), ESR-2 (0.016 wt.% Y) and ESR-3 (0.042 wt.% Y)) were investigated. Further, the number of inclusions in ESRed steel was observed to obviously decrease, and the distributions were more uniform. The fine Y-Al-O inclusions (1-2 ㎛) were the main inclusions in ESR-2. The addition of Y affected the prior austenite grain size (PAGZ), increasing the tensile strength at test temperature. Low ductile-brittle transition temperature (DBTT) was obtained because of the fine PAGZ and dispersive inclusions. For the ESRed CLAM steel with 0.016 wt.% Y, the yield strengths were 621 MPa at 20 ℃ and 354 MPa at 600 ℃ in air. Further, the uniform elongation and elongation of the ESR-2 alloy were 5.5% and 20.1% at 20 ℃, respectively. Meanwhile, the DBTT tested using full-size Charpy impact specimen (55 cm × 10 cm × 10 cm) was reduced to -83 ℃.

• Metals and materials international
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• v.24 no.6
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• pp.1221-1231
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• 2018

The effect of strain aging on tensile behavior and properties of API X60, X70, and X80 pipeline steels was investigated in this study. The API X60, X70, and X80 pipeline steels were fabricated by varying alloying elements and thermomechanical processing conditions. Although all the steels exhibited complex microstructure consisting of polygonal ferrite (PF), acicular ferrite, granular bainite (GB), bainitic ferrite (BF), and secondary phases, they had different fractions of microstructures depending on the alloying elements and thermomechanical processing conditions. The tensile test results revealed that yielding behavior steadily changed from continuous-type to discontinuous-type as aging temperature increases after 1% pre-strain. After pre-strain and thermal aging treatment in all the steels, the yield and tensile strengths, and yield ratio were increased, while the uniform elongation and work hardening exponent were decreased. In the case of the X80 steel, particularly, the decrease in uniform elongation was relatively small due to many mobile dislocations in PF, and the increase in yield ratio was the lowest because a large amount of harder microstructures such as GB, BF, and coarse secondary phases effectively enhanced work hardening.

• Transactions of Materials Processing
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• v.7 no.6
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• pp.610-619
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• 1998

The superplastic blow forming technology has advantages of cost reduction and low material consumption. compared to the conventional sheet metal forming technology due to the capability of precisely forming with high elongation and low flow stress. however it has a disadvantage that its partial thickness distribution is non-uniform. A processing technology like diaphragm forming has been developed even though it is difficult to prepare materials for superplastic blow forming. in this study a hemisphere forming of sheet before superplastic forming. It was found that the rotary forming material was less in quantity of cavitation at pole than that of hemisphere part that was superplastic formed without rotary forming treatment. Also discussed are the critical strain which is closely related to cavity shape and size.