• Title/Summary/Keyword: Heat Input

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Effects of microstructure and welding heat input on the toughness of weldable high strength steel weldments (용접구조용 고장력강의 용접부 인성에 미치는 미세 조직과 용접 입열량의 영향)

  • 장웅성;방국수;엄기원
    • Journal of Welding and Joining
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    • v.7 no.3
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    • pp.44-54
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    • 1989
  • This study was undertaken to evaluate the allowable welding heat input range for high strength steels manufactured by various processes and to compare the weldability of TMCP steel for high heat input welding with that of conventional Ti-added normalized steel. The allowable welding heat input ranges for conventional 50kg/$mm^2$ steel to guarantee D or E grade of ship structural steel were below 150 and 80kJ/cm respectively. Such a limit in welding heat input was closely related with the formation of undesirable microstructures, such as grain boundary ferrite and ferrite side plate in the coarse grain HAZ. In case of 60 and 80kg/$mm^2$ quenched and tempered steels, for securing toughness in weldments over toughness requirements for base metal, each welding heat input had to be restricted below 60 and 40kJ/cm, that was mainly due to coarsened polygonal ferrite in weld metal and lower temperature transformation products in coarse grain HAZ. The TMCP steel could be appropriate as a grade E ship hull steel up to 200kJ/cm, but the Ti-added normalized steel could be applied only below 130kJ/cm under the same rule. This difference was partly owing to whether uniform and fine intragranular ferrite microstructure was well developed in HAZ or not.

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Effects of Mn and Heat-input on the Mechanical Properties of EGW Welds (일렉트로 가스 용접부의 기계적 성질에 미치는 Mn 및 입열량의 영향)

  • Kim, Nam In;Jeong, Sang Hoon;Lee, Jeong Soo;Kang, Sung Won;Kim, Myung Hyun
    • Korean Journal of Metals and Materials
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    • v.47 no.3
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    • pp.195-201
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    • 2009
  • This paper is concerned with effects of Mn and heat-input on the mechanical properties of EGW welds. Four different kinds of welding consumables were fabricated by varying Mn contents such as 1.3, 1.5, 1.7, 2.0%Mn and each consumable was welded for EGW on four heat-input conditions between 190 and 340 KJ/Cm. Mn contents were decreased as heat-input increases and alloy elements (C, Si, Ti, B, Al) to deoxidize easily also revealed similar tendency to Mn. Their microstructure, Charpy impact property and strength were investigated, and it is found that Charpy impact property and strength exhibit a strong dependence on change of microstructure by Mn contents and heat-input. The increase of Mn contents or the decrease of heat-input made the microstructure fine and increase volume fraction of acicular ferrite, thereby leading to the great improvement of Charpy impact property and strength. In case of single EGW, optimum Mn contents are over 1.7% for the toughness and strength.

A study on the Mechanical Properties in High Heat Input Welds of High Strength Steels (大入熱 高張力鋼 熔接部 의 機械的 特性 變化 에 關한 硏究)

  • 김영식;배차헌
    • Journal of Welding and Joining
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    • v.1 no.1
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    • pp.47-55
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    • 1983
  • The mechanical and microstructural properties in high heat input welds of home-made SM 50 high strength steels were investigated and compared with the manual shielded metal arc welds. Also, the fracture toughnesses of the simulated weld-bonds with various thermal cycles were quantatively examined in order to provide the basic data for further development of the high strength steels for high input welding. Main results obtained are as follows. (1) The embrittlement degree and the coarse grained region in high heat input welds appear to be extraordinarily large compared with the manual shielded metal arc welds, while the difference in change of nicrohardness is not so large in both welds. (2) The embrittleness in high heat input weld-bonds is mainly affected by the size of coarse grain rather than the microstructure. (3) The fracture toughness in high heat input weld-bonds can be improved by controlling the cooling rate from 800.deg.C to 500.deg.C rapidly.

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Evaporation Cooling of Droplet due to Surface Roughness under Radiative Heat Input Condition (복사가열조건에서 표면 거칠기에 따른 액적의 증발 냉각)

  • Bang Chang-Hoon;Kwon Jin-Sun;Yea Yong-Taeg
    • Journal of the Korean Society of Safety
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    • v.19 no.3 s.67
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    • pp.14-19
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    • 2004
  • The objective of the present work is to examine evaporation cooling of droplet due to surface roughness under radiative heat input condition. The surface temperatures varied from $80\~160^{\circ}C$ on aluminum alloy (AL 2024) and surface roughness was $0.18{\mu}m,\;1.36{\mu}m$. The results are as follows; Regardless of surface roughness under radiative heat input condition, as droplet diameter is larger, the in-depth temperature of solid decreases and evaporation time increases. In the case of $0.18{\mu}m\;and\;1.36{\mu}m$ of surface roughness, the larger the surface roughness is, the less the evaporation time is and the larger the temperature within the solid is. In the case of $Ra=0.18{\mu}m$ evaporation time and time averaged heat flux for radiative heat input case is shorter than for the conductive case.

A Study of Arc Modeling and Heat Input Distribution on the Surface during Torch Weaving in Gas Metal Arc Welding (가스 메탈 아크 용접에서 토치 위빙 중 아크 모델링 및 표면 입열 분포 해석에 관한 연구)

  • Kim, Yong-Jae;Rhee, Se-Hun
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.1
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    • pp.162-170
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    • 2001
  • In torch weaving in arc welding on V groove, the heat input distribution on groove surface is a main factor determining the bead shape and the weld quality with and without the weld defects such as undercut, overlap, etc. In this study, we calculate the heat input varying with the welding current, arc voltage, welding speed and the touch weaving condition using numerical method. And we investigate the heat input distribution on groove surface while applying the various grooves having 2 dimensional heat sources.

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The effect of welding heat input and heat-treatment on the strength of the electron beam welded $175Kg/mm^2$ maraging steel sheet (전자비임용접한 $175Kg/mm^2$급 박판 Maraging강의 이음강도에 미치는 용접입열 및 열처리의 영향)

  • 윤한상;정병호;배차헌
    • Journal of Welding and Joining
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    • v.4 no.2
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    • pp.21-29
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    • 1986
  • The influence of welding heat input variation(600-900J/cm) and heat-treatment condition after welding on tensile strength of butt welded joint in $175Kg/mm^2$ strength level Maraging steel(Co-free and Co-containing) sheets was investigated on the basis of hardness distribution, microstructure of weld metal and fracture surface. The obtained main results are as follows; 1. The strength of weldment (UTS, NTS), joint efficiency showed a little decreasing tendency with the increase in welding heat input, and the elongation showed a little increasing tendency with the increase in the width of weld metal. It was considered because of the plastic constraint of the high strength base metal. 2. The strength of weldment was better in the solution treatment and aging than the aging only after welding due to the disappearance of almost denverite in weld metal. 3. The hardness distribution in weldment after welding and heat-treatment was almost similar to both Co containing and Co free Maraging steel with change in welding heat input. 4. The fracture was occurred at weld metal, and the fracture surface showed a relatively shallow dimples in both Co containing and Co free Maraging steel.

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The Effect of Ferrite Ratio on the Properties of PWHT Overlaid Welds (Duplex SS 육성 용접부의 물성에 미치는 열처리전 페라이트 함량의 영향)

  • Seong, Hui-Jun;Kim, Yeong-Il;Seo, Chang-Gyo
    • Proceedings of the KWS Conference
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    • 2005.06a
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    • pp.294-296
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    • 2005
  • Several duplex overlaied-weldments which have different ferrite ratio were prepared by changing welding heat input ant post weld heat treatment were carried out to understand the effect of the ferrite ratio on the precipitation during post weld heat treatment. High heat input weldment indicated low ferrite ratio, while low heat input weldment has high ferrite ratio. Low ferrite ratio weldment showed much and faster precipitation. But high ferrite ratio weldment showed less and slower precipitation.

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The Arc Brazing by Variable Polarity AC Pulse MIG Welding Machine (극성가변 AC 펄스 MIG용접기를 이용한 아크 브레이징)

  • 조상명;공현상
    • Journal of Welding and Joining
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    • v.21 no.4
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    • pp.56-62
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    • 2003
  • MIG brazing is used for many parts without melting base metal because of high productivity. Pulsed MIG brazing can be used to further reduce heat input and to improve the process stability. However, a significant amount of zinc in galvanized sheet steel is burned off in the area of brazes. Therefore, the brazing method to reduce the heat input is needed. In the brazing for galvanized sheet steel, variable polarity AC pulse MIG arc brazing can be applied to more decrease the heat input by setting EN-ratio adequately. In this research, we studied for the variable polarity AC pulse MIG arc brazing to decrease the heat input by using ERCuSi-A wire. As the result of increasing EN-ratio, melting ratio of base metal and burning off of zinc were reduced in galvanized sheet steel.

A Study on the Formation of Cavity and Welding Property in the Laser Welding Fusion Zone between Sintered Segment and Mild Steel Shank (소결체와 저탄소강의 레이저용접시 생성되는 캐비티의 형성과 용접 특성에 대한 연구)

  • Cho Nam-Joon;Jung Woo-Gwang;Kim Sung-Wook;Lee Chang-Hee;Kim Sung-Dea
    • Korean Journal of Materials Research
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    • v.14 no.4
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    • pp.300-306
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    • 2004
  • A laser welding has been made between sintered tip of Fe-Co-W and low carbon steel shank for the diamond saw blade. The welding characteristics and formation of defect has been investigated carefully for the weld fusion zone in different welding condition. Full penetration has been observed for the whole range of heat input investigated in the present work. Bead width and under-fill have been increased with the increase of heat input. With increasing of heat input small cavities were decreased while large cavities were increased. The ratio of total cavity area to the entire weld bead area was not changed significantly with change of heat input. Most of cavities were found near the tip, and supposed to be formed from the pore in the tip.

Cr-Mo鋼 熔接熱影響部의 破壞靭性과 熔接入熱量에 관한 硏究 II

  • 임재규;정세희
    • Journal of Welding and Joining
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    • v.5 no.2
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    • pp.9-16
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    • 1987
  • Post weld heat treatment (PWHT) is carried out to increase the fracture toughness in heat affected zone(HAZ) and remove the residual stress. There occur some problems such as toughness decreement and stress relief cracking(SRC) in the coarse grained HAZ subjected to the effect of tempering treatment. Especially, embitterment of structure directly relates to the mode of fracture and is appeared as the difference of fracture surface, that is, grain boundary failure. Therefore, in this paper, PWHT was carried out under the stress of 0, 10, 20 and $30kg/cm^2$ to simulate residual stress in HAZ welded by heat input of 10, 30 and 40KJ/cm. Applied stress in weld HAZ during PWHT assisted precipitin of over saturated alloying element in the structure, and grain boundary failure according to welding heat input didn't almost appear at the heat input of 10 KJ/cm, but it appeared from being the applied stress of $30kg/cm^2$ at $30KJ/cm and 20kg/mm^2$ at 40KJ/cm.

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