• Journal of Welding and Joining
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• 제21권3호
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• pp.30-34
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• 2003

This paper describes the heat distribution characteristics of ASTM A131DH36 high tensile steel for ship structures in 5㎾ $CO_2$ laser welding. In general, high energy of laser beam concentrates on the small area of the weldment instantaneously; therefore, this heat transfer mechanism induces the rapid changes of temperature and mechanical characteristics in laser welds this mechanism. So temperature distribution analysis is important to understand mechanical characteristics of laser welds. Authors have conducted finite element simulation to analyze the heat distribution characteristics in laser welds. The result of simulation has been verified by comparing with the metallurgical experiment result. From the result of this study, we can accurately predict the heat distribution characteristics in laser welds by using numerical simulation.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.250-256
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• 2004

For many years and primarily for economical reasons, Dissimilar Metal Welds have been used as transition joints in a variety of equipment and applications. But Dissimilar Metal Welds have several fabrication and metallurgical drawbacks that can often lead to in-service failures. In this paper, the laser weldability of STS304 stainless steel and SM45C at dissimilar metal welds using a continuous wave Nd:YAG laser are experimentally investigated. An experimental study was conducted to determine effects of welding parameters, on eliminating or reducing the extent welding zone formation at dissimilar metal welds and to optimize those parameters that have the most influence parameters such as focus length, power, beam speed, shielding gas, and wave length of laser were tested.

• Journal of Welding and Joining
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• 제3권2호
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• pp.1-9
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• 1985

In this study, the influence of carbon equivalents on friction welds of similar steels was investigated. Four types of steels with 15mm diameter tested in the wide range of carbon equivalents from 0.3 to 1.1 Main experimental results are summarized as follows : (1) Under the constant burn-off length, the friction time becomes longer with the increasing carbon equivalent, but the upset length shows no consistent tendencies. (2) Due to the recrystallization in the contact area, the maximum hardness occurs some away from the contact surface. And it increases almost linearly with the increasing carbon equivalent. (3) Even a steel with 1.1 C.E. can be friction welded to make defect-free welds. (4) With the increasing carbon equivalent, the bend angle and charpy impact value decrease very rapidly in the range from 0.3 C. E., but remain nearly unchanged for C. E. higher than 0.6. (5) Heat treatment of the base metals before welding has very little influence on the mechanical properties of welds. On the other hand, normalizing of the welds improves the bend angle and charpy impact value, but its effect becomes almost negligible, when the carbon equivalents are higher than 0.6.

• Journal of Welding and Joining
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• 제7권4호
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• pp.22-29
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• 1989

In this paper weld distortion both in butt and fillet welds by flux cored arc welding has been investigated by changing welding parameters such as heat input and plate thickness, and the weld distortion was expressed as a function of welding parameters adopting the inherent strain theory as proposed by Watanabe and Satoh in 1961. As results of the research it is proposed that transverse shrinkage in root pass butt welds in proportional to ln[(Q/t_-tan.theta.] where Q is heat input(cal/mm), t is plate thickness(mm), and 2.theta. is groove angle(degree), and angular distortion .phi.(radian) in one pass of fillet welds has the following relationship: .phi..var.(Q/ $t^{1.5}$)$^{3}$exp[-(Q/ $t^{1.5}$ )$^{2}$3/] These equations provide us with basic tools to predict the amount of weld distortion in welded structures.

• Nuclear Engineering and Technology
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• 제49권3호
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• pp.651-661
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• 2017

The Korea Institute of Nuclear Safety, as a representative organization of Korea, in February 2012 participated in an international Program to Assess the Reliability of Emerging Nondestructive Techniques initiated by the U.S. Nuclear Regulatory Commission. The goal of the Program to Assess the Reliability of Emerging Nondestructive Techniques is to investigate the performance of emerging and prospective novel nondestructive techniques to find flaws in nickel-alloy welds and base materials. In this article, Korean round-robin test results were evaluated with respect to the test blocks and various nondestructive examination techniques. The test blocks were prepared to simulate large-bore dissimilar metal welds, small-bore dissimilar metal welds, and bottom-mounted instrumentation penetration welds in nuclear power plants. Also, lessons learned from the Korean round-robin test were summarized and discussed.

• International Journal of Korean Welding Society
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• 제3권1호
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• pp.17-22
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• 2003

During the laser welding, weldments are suddenly heated and cooled by laser beam of high density energy. This phenomenon gives an occasion to complex welding residual stresses, which have a great influence on structural instability, in laser welds. However, relevant researches on this field are not sufficient until now and residual stress measurements have experimental and practical limitations. From these reasons, a numerical simulation may be attractive in order to solve the residual stress problem. For clarifying the distribution of heat and welding residual stresses in laser welds with the nail-head shape, authors conduct the finite element analysis (two-dimensional unstationary heat conduction & thermal elastic and plastic analysis). From the results, we can confirm the stress concentration occurs at the place of melting line shape changed in laser welds with the nail-head shape.

• Journal of Welding and Joining
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• 제20권6호
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• pp.22-22
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• 2002

• 동력기계공학회지
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• 제14권2호
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• pp.71-77
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• 2010

This paper was studied on microstructure, mechanical properties and corrosion characteristics of 316L stainless steel pipe welds was fabricated by orbital welding process. S-Ar specimen was fabricated by using Ar purge gas and S-$N_2$ specimen was fabricated by using $N_2$ purge gas. Ferrite was not detected in weld metal of S-$N_2$ specimen but the order of 0.13 Ferrite number(FN) was detected in weld metal of S-Ar specimen. Oxygen and Nitrogen concentration of S-$N_2$ specimen was higher than S-Ar specimen on HAZ and inner bead. The welds microstructural characteristics of S-Ar and S-$N_2$ specimens are similar. The microvickers hardness values of S-Ar and S-$N_2$ specimens welds were similar and average values of each regions were in the range of 174~194. The microstructures of S-Ar and S-$N_2$ weld metal were full austenite by primary austenite solidification. The Solidification structures of S-Ar and S-$N_2$ weld metal were formed directional dendrite toward bead center. The potentiodynamic polarization curve of STS 316L pipe welds exhibited typical active, passive, transpassive behaviour. Corrosion current density$(I_{corr.})$ and corrosion rate values of S-Ar specimen in 0.1M HCl solution were $0.95{\mu}A/cm^2$ and $0.31{\mu}A$/year respectively. The values of S-$N_2$ specimen were $1.4{\mu}A/cm^2$ and $0.45{\mu}m$/year.

• 대한기계학회논문집A
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• 제36권2호
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• pp.137-148
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• 2012

가압경수로의 많은 관통관 중에서 니켈 기저 합금인 Inconel alloy 600 계열의 이종금속용접부는 일차수응력부식균열에 민감하며, 이를 평가하기 위하여 용접부에 작용하는 잔류응력분포를 정확히 예측하는 것이 중요하다. 본 논문에서는 유한요소해석을 이용하여 노즐 맞대기 이종금속용접부에 작용하는 일반적인 잔류응력분포를 예측하였다. 이를 위해 노즐 맞대기 이종금속용접부의 형상을 단순화하여 특정한 형상 변수에 따른 용접부 잔류응력분포를 확인하였으며, 이를 토대로 기존 문헌에 제시된 오스테나이트계 배관 맞대기 용접부 잔류응력 분포식을 수정하여 가압경수로 노즐 맞대기 이종금속용접부에 작용하는 일반적인 잔류응력분포 예측식을 제시하였다.

• Journal of Welding and Joining
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• 제32권2호
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• pp.48-53
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• 2014

This study was carried out to investigate the effect of postweld heat treatment(PWHT, 930, 1080, $1230^{\circ}C$) on the microstructure, phase formation, pitting corrosion and mechanical properties such as hardness, tensile strength and impact values of super duplex stainless steel(UNS S32750) multipass welds. Based on the microstructural examination and X-ray diffraction analysis, it was found that the ${\sigma}$ phase was formed in the welds heat treated at $930^{\circ}C$ in which the ferrite content greatly decreased into 5~10% in the welds. The secondary austenite was formed in the reheated zone of welds and redissolved into ferrite with increasing heat treatment temperatures. The tensile strength and impact values of welds heat treated at $930^{\circ}C$ were the lowest and revealed the brittle fracture surface. The weight loss by pitting corrosion increased with test temperatures. It was confirmed that pitting corrosion occurred mainly in secondary austenite of reheated zones. The postweld heat treatment temperature is recommended to be in the range of $1050{\sim}1150^{\circ}C$.