Microstructure and High Temperature Properties of the Dissimilar Weld between Ferritic Stainless Steel and Carbon Steel

김정길,강정윤,홍승갑,강기봉 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.5

Dissimilar joints between STS441, a ferritic stainless steel, and SS400, a carbon steel, were welded by GMAW (Gas Metal Arc Welding) using STS430LNb as a welding wire. The fracture behavior of the dissimilar weld was analyzed by a microstructural observation and thermo-mechanical tests. Martensite was formed at the region between SS400 and the weld metal because the Cr and Nb content in this region decreased due to the dilution of SS400 carbon steel during welding. According to results from a high temperature tensile test with a specimen aged at 900 °C, it was found that the tensile strength of the dissimilar weld at high temperature was equal to that of STS441 base metal and the formation of martensite had little influence on tensile strength of the dissimilar weld at high temperature. However, in the case of thermal fatigue resistance, the dissimilar weld had an inferior thermal fatigue life to STS441 because of the presence of martensite and the softened region around the interface between the dissimilar weld metal and SS400. Dissimilar joints between STS441, a ferritic stainless steel, and SS400, a carbon steel, were welded by GMAW (Gas Metal Arc Welding) using STS430LNb as a welding wire. The fracture behavior of the dissimilar weld was analyzed by a microstructural observation and thermo-mechanical tests. Martensite was formed at the region between SS400 and the weld metal because the Cr and Nb content in this region decreased due to the dilution of SS400 carbon steel during welding. According to results from a high temperature tensile test with a specimen aged at 900 °C, it was found that the tensile strength of the dissimilar weld at high temperature was equal to that of STS441 base metal and the formation of martensite had little influence on tensile strength of the dissimilar weld at high temperature. However, in the case of thermal fatigue resistance, the dissimilar weld had an inferior thermal fatigue life to STS441 because of the presence of martensite and the softened region around the interface between the dissimilar weld metal and SS400.

Boundary element analysis of stress singularity in dissimilar metals by friction welding

정남용,C.-H. Park 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.9

Friction-welded dissimilar metals are widely applied in automobiles, rolling stocks, machine tools, and various engineering fields. Dissimilar metals have several advantages over homogeneous metals, including high strength, material property, fatigue endurance, impact absorption, high reliability, and vibration reduction. Due to the increased use of these metals, understanding their behavior under stress conditions is necessary, especially the analysis of stress singularity on the interface of friction-welded dissimilar metals. To establish a strength evaluation method and a fracture criterion, it is necessary to analyze stress singularity on the interface of dissimilar metals with welded flashes by friction welding under various loads and temperature conditions. In this paper, a method analyzing stress singularity for the specimens with and without flashes set in friction-welded dissimilar metals is introduced using the boundary element method. The stress singularity index (λ ) and the stress singularity factor ( Γ ) at the interface edge are computed from the stress analysis results. The shape and flash thickness, interface length, residual stress, and load are considered in the computation. Based on these results, the variations of interface length (c) and the ratio of flash thickness (2 1t t ) greatly influence the stress singularity factors at the interface edge of friction-welded dissimilar metals. The stress singularity factors will be a useful fracture parameter that considers stress singularity on the interface of dissimilar metals.

A Review on Welding of Dissimilar Metals in Car Body Manufacturing

Md. Abdul Karim,Yeong-Do Park 대한용접·접합학회 2020 대한용접·접합학회지 Vol.38 No.1

This paper presents a comprehensive study of the metallurgical challenges of welding dissimilar metals. It also describes the important factors in dissimilar welding which need to be considered for automotive applications. It further investigates effective approaches to overcome these present challenges. Steels, aluminum alloys, and magnesium alloys are widely used metals in car bodies. However, it is difficult to weld these dissimilar metals and achieve good joint quality, due to their inherent disparate properties. The formation of brittle, crack sensitive and corrosion susceptible intermetallic phases is the main obstacle to dissimilar weld quality. Various approaches have been attempted by many researchers to enhance the performance of dissimilar welds. The most notable efforts include the application of interlayers, cover plate, least heat input, a combination of welding and mechanical joining, and alloying elements of filler metals. Based on considerations of joint performance, production cost and time, present industry infrastructure, and so on, the most effective and feasible approaches were identified which required the least amount of heat input, and the appropriate filler metal alloying elements.

이종 금속의 아크 스폿 용접성 및 접합부 형상 예측에 관한 연구

김기순,장경복,강성수 대한용접접합학회 2000 대한용접·접합학회지 Vol.18 No.2

In this study, the lap welding between austenitic stainless steel and carbon steel was carried out using arc spot welding process and weldability of welded specimens was estimated. From the tensile-shear strength test, micro Vickers harness test, and microstructure observation, specimen of $psi6.5mm$(hole of upper plate) showed the best results in terms of tensile-shear strength and nugget shape. And there was an unmix zone in fusion boundary between the carbon steel base metal and bulk weld metal. This zone had very width with the hard microstructure. The shape of weld nugget in arc spot welding of dissimilar metal melds was predicted by searching thermal history of a weld joint through a three-dimensional finite element model. From the numerical analysis, predicted the shape of weld nugget showed good agreement with the experiment.

유한요소해석을 이용한 노즐 이종금속용접부의 용접잔류응력 예측

허남수(Nam-Su Huh),김종욱(Jong-Wook Kim),최순(Suhn Choi),김태완(Tae-Wan Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

The primary water stress corrosion cracking (PWSCC) of dissimilar metal weld based on Alloy 82/182 is one of major issues in material degradation of nuclear components. It is well known that the crack initiation and growth due to PWSCC is influenced by material’s susceptibility to PWSCC and distribution of welding residual stress. Therefore, modeling the welding residual stress is of interest in understanding crack formation and growth in dissimilar metal weld. Currently in Korea, a numerical round robin study is undertaken to provide guidance on the welding residual stress analysis of dissimilar metal weld. As a part of this effort, the present paper investigates distribution of welding resisual stress of a ferritic low alloy steel nozzle with dissimilar metal weld using Alloy 82/182. Two-dimensional thermo-mechanical finite element analyses are carried out to simulate multi-pass welding process on the basis of the detailed design and fabrication data. The present results are compared with those from other participants, and more works incorporating physical measurements are going to be performed to quantify the uncertainties relating to modelling assumptions.

유한요소법을 이용한 용접공정 모사 시 입열 방법에 따른 용접잔류응력의 영향

양준석(Jun-Seog Yang),박치용(Chi-Yong Park),이경수(Kyoung-Soo Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

This paper is to discuss distribution of welding residual stresses of a ferritic low alloy steel nozzle with dissimilar metal weld using Alloy 82/182. Two dimensional (2D) thermo-mechanical finite element analyses are carried out to simulate multi-pass welding process on the basis of the detailed and fabrication data. On performing the welding analysis generally, the characteristics on the heat input and heat transfer of weld are affected on the weld residual stress analyses. Thermal analyses in the welding heat cycle process is very important process in weld residual stress analyses. Therefore, heat is rapidly input to the weld pass material, using internal volumetric heat generation, at a rate which raises the peak weld metal temperature to 2200 ℃ and the base metal adjacent to the weld to about 1400 ℃. These are approximately the temperature that the weld metal and surrounding base materials reach during welding. Also, According to the various ways of appling the weld heat source, the predicted residual stress results are compared with measured axial, hoop and radial through-wall profiles in the heat affected zone of test component. Also, those results are compared with those of full 3-dimensional simulation.

노즐 이종용접부 잔류응력에 미치는 동종용접의 영향 평가

유승천(Seung Cheon Yu),정재욱(Jae Uk Jeong),장윤석(Yoon Suk Chang),김영진(Young Jin Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

Determination of weld-induced residual stress has been an important issue in nuclear power industry because several failures were reported in dissimilar metal weld parts due to primary water stress corrosion cracking. In this context, a couple of remarkable round robin analyses were conducted to quantify the welding simulation variables and to establish optimized numerical analysis process. The purpose of the present research is to introduce welding simulation results for a safety and relief nozzle, which has a dissimilar metal weld part as well as a similar metal weld part. First, finite element analyses are carried out to calculate residual stresses at the inside of nozzle considering only dissimilar metal welding. Subsequently, residual stresses taking into account both the dissimilar and similar metal welding are computed. The similar metal weld effect is evaluated by comparing these analysis results and technical findings derived from the evaluation are fully discussed.

Al/Fe 이종재의 마이크로 마찰교반 맞대기용접 적용성 평가

유현정(Hyeonjeong You),안영남(Youngnam Ahn),이성(Sung Yi),현승균(Soongkeun Hyun),김철희(Cheolhee Kim) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.3

In the automobile industry, there is an increasing demand for Al/Fe dissimilar metal joining. Friction stir welding (FSW) is an efficient solid-state welding method to achieve high-quality Al/Fe dissimilar metal welding. Here, we reviewed the previous studies on butt FSW of thin Al/Fe sheets and conducted feasibility tests to investigate the applicability of micro FSW with a base material thickness of 1 mm or less. Most of the past literature, except for one study that adopted 1.12 mm-thick specimens, has worked with a base metal thickness of 1.5 mm or more. Selecting appropriate parameters can lead to a weld strength that is more than 90% of the base metal strength. Through feasibility tests on 2 mm-thick specimens, we could derive the welding conditions to obtain sound welds and the required joint strength. An adequate range (0.5-0.75 mm/rev) of advance per revolution was recommended to ensure the weld strength. A feasibility test on 1 mm-thick specimens revealed the possibility of melting of Al base metal during FSW of 1 mm-thin sheets; moreover, a low tool rotation speed was found to be crucial in ensuring the weld joint strength. The maximum weld strength for 1 mm-thick specimens was 200 MPa, which is 117% of the required weld strength.

인코넬 82/182 이종금속 용접부의 기계물성 평가

이정훈(Jounghoon Lee),장창희(Changheui Jang),김종성(Jong Sung Kim),진태은(Tae Eun Jin) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5

In several locations of the pressurized water reactors, dissimilar metal welds using inconel welding wires are used to join the low alloy steel nozzles to stainless steel pipes. To evaluate the integrity and design the dissimilar welds, tensile and fracture properties variations are needed. In this study, dissimilar metal welds composed of SA508 Gr.3 LAS, inconel 82/182 weld, and TP316 stainless steel were prepared by gas tungsten arc welding and shielded metal arc welding technique. Microstructures were observed using optical and electron microscopes. Different tensile and fracture properties were observed depending on the specimen sampling position at room temperature and 320℃, and that was discussed based on the microstructure characteristics. It was found that the strength at the bottom of weld was greater than at the top of the weld. Also, from the test data using small punch specimen, more detailed tensile property variations were evaluated.

가압경수로 노즐 맞대기 이종금속용접부의 용접잔류응력 예측

김지수(Ji Soo Kim),김주희(Ju Hee Kim),배홍열(Hong Yeol Bae),오창영(Chang Young Oh),김윤재(Yun-Jae Kim),이경수(Kyung soo Lee),송태광(Tae Kwang Song) 대한기계학회 2012 大韓機械學會論文集A Vol.36 No.2

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 형상변수에 따른 용접부 잔류응력분포를 확인하였으며, 이를 토대로 기존 문헌에 제시된 오스테나이트계 배관맞대기 용접부 잔류응력 분포식을 수정하여 가압경수로 노즐 맞대기 이종금속용접부에 작용하는 일반적인잔류응력분포 예측식을 제시하였다. In pressurized water nuclear reactors, dissimilar metal welds are susceptible to primary water stress corrosion cracking. To access this problem, accurate estimation of welding residual stresses is important. This paper provides general welding residual stress profiles in dissimilar metal nozzle butt welds using finite element analysis. By introducing a simplified shape for dissimilar metal nozzle butt welds, changes in the welding residual stress distribution can be seen using a geometry variable. Based on the results, a welding residual stress profile for dissimilar metal nozzle butt welds is proposed that modifies the existing welding residual stress profile for austenitic pipe butt welds.