• Title/Summary/Keyword: FCA 용접

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An Analytical Solution for Transient Temperature Distribution in Fillet Arc Welding Including the Effect of Molten Metal (용착 금속을 고려한 필릿 용접에서 온도 분포 예측을 위한 해석적 모델)

  • 정선국;조형석
    • Journal of Welding and Joining
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    • v.13 no.3
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    • pp.116-124
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    • 1995
  • This paper presents an analytical solution to predict the transient temperature distribution in fillet arc welding including the effect of molten metal. The solution is obtained by solving a transient three-dimensional heat conduction equation with convection boundary conditions on the surfaces of a plate, and mapping the infinite plate onto the fillet weld geometry with energy equation. The electric heat input on the fillet weld and on the infinite plate is assumed to have a combination of two bivariate Gaussian distribution. To check the validity of the solution. FCA welding experiments were performed under various welding conditions. The actual isotherms of the weldment cross-sections at various distances from the arc start point are compared with those of simulation result.

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Development of an Effective Arc Sensing Algorithm for Seam-Tracking in Flux-Cored Arc Welding Process for Horizontal Fillet Joints (FCAW 수평 필릿용접용 용접선추적을 위한 아크센싱 알고리즘 개발)

  • 권순창;최재성;장낙영
    • Journal of Welding and Joining
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    • v.15 no.1
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    • pp.66-80
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    • 1997
  • This paper describes a newly developed arc-sensing algorithm of seam-tracking for FCA W (flux-cored arc welding) horizontal fillet welding. In this algorithm, arc current and the Weighted-Are-Current (WAC) are used to adjust the position of a weld torch in directions of bead throat and weaving, respectively. The WAC, which is newly devised in this study, means that arc current in the vicinity of weaving end is more emphasized than that in the center of weaving. The reason of this is because there usually exists much noise in the center of weaving due to abrupt change of arc length in case some empty gaps exist in a fillet joint Variance analysis was performed in order to check the effect of weld parameters on arc current and the WAC. As a result, the relationships between tip-to-workpiece distance and arc current, and between weaving offset and the WAC were established.To check "the validity of the algorithm, seam-tracking experiments were performed ;mder various welding condition. The result of experiments showed a satisfactory tracking performance in the presence of empty gaps in a horizontal fillet joint.et joint.

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Study of the welding monitor and characteristics according to a change in Gas mixture by FCAW (FCAW의 혼합가스 변화에 따른 용접 모니터링과 특성에 관한 연구)

  • Lim, Byung-Chul;Kang, Chul-Soon;Park, Sang-Heup
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.10
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    • pp.5933-5938
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    • 2014
  • In this study, the effect of varying the mixture gas during FCA welding was studied for an Atos 60 test piece. To examine the characteristics of welding, the weldability of the material was checked before welding and online monitoring was performed to examine the mechanical properties after welding. The mixture Ar 80% + $CO_2$ 20% at low speed gave very elegant beads with very little spatter. 100% $CO_2$ gave rise to high spatter generation. For Ar 80% + $CO_2$ 20%, the low current region due to the normal short circuits created spatter, which was more than double for 100% $CO_2$. This peak distribution occurred due to the instability of the arc. The tensile test result for Ar 80% + $CO_2$ 20%, Ar 90%+ $CO_2$ 10% and $CO_2$ 100% at 511MPa, 507MPa, and 469MPa showed that the yield strength was improved by 8.1 and 8.9% for 80%+ $CO_2$ 20% and Ar 90%+ $CO_2$ 10%, respectively, compared to 100% $CO_2$. The tensile test result at 622MPa, 609MPa, and 581MPa showed that the yield strength was improved by 7.0% for both the mixture gas compared to 100% $CO_2$.

A Study on the Effect of Heat Input on the Microstructure and Toughness of Weldments Made by Domestic Flux Cored Wires. (국산 플럭스 코어드 와이어 용접에서 입열량이 용접부의 미세조직과 인성에 미치는 영향)

  • 고진현;국정한
    • Journal of Welding and Joining
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    • v.11 no.4
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    • pp.57-69
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    • 1993
  • In the present study, the microstructure and Charpy V notch toughness of multipass $CO_2$ FCA weldment in three different heat inputs(1-3KJ/mm)were investigated. The weldments using two different domestic FCAW wires(AWS E71T-1 and E71T-5 equivalent) in C-Mn steel were chemically analysed. The following conclusions can be inferred. 1. T-1 wire Showed a stable arc transfer, less spatter and harsh, a better bead spreading and easy slag removal, whereas T-5 wire suffered from the arc stability, which tended to increase spatter and produce a more convex bead. 2.The microsturctures of the top beads of the weldments in three different heat inputs consisted of coarse-grained boundary ferrite and Widmanstatten ferrite side plate with increasing heat inputs. The modest fraction of acicular ferrite in the two wire weldments was observed in the 2KJ/mm heat input. 3.The fine-grained reheated zones of both welds consisted of a duplex microstructure of polygonal ferrite and second phases. 4. The basic flux weldment of T-5wires showed a higher Charpy impact property than that of T-1 wires because of a higher fraction of acicular ferrite in the weld microstructure.

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Numerical Analysis of Welding Residual Stresses for Ultra-thick Plate of EH40 TM and API 2W Gr.50 Steel Joined by Flux Core Arc Welding (EH40과 API2W강재의 극 후판재 다층 FCAW 버트 접합부 잔류응력해석)

  • Hwang, Se-Yun;Lee, Jang-Hyun;Yang, Young-Sik;Lee, Sung-Je;Kim, Byung-Jong
    • Journal of Welding and Joining
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    • v.28 no.3
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    • pp.65-72
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    • 2010
  • Some structural members of large-scale marine vessels such as large-scale offshore structures and very large container ships are assembled by very thick plates of which thickness exceeds 60mm. Also, high-tensile steels have been selected to meet the required structural strength and fatigue strength. Generally, multi-pass welding method such as FCA(Flux-Core Arc) welding has been used to join the thick plates. Considering the welding residual stresses, fatigue strength of the welded joints of thick plates should be assured since the residual stress influences the fatigue strength. This paper presents a numerical procedure to investigate the residual stress of structure joined by multi-pass FCA welding so that it can be incorporated into the fatigue strength assessment considering the effect of welding residual stress. The residual stress distribution is also measured by X-Ray diffraction method. The residual stress obtained by the computational model also has been compared with that of experiment. The results of FEA are in very good agreement with the experimental measurements.

Hydrogen Embrittlement Resistance and Diffusible Hydrogen Desorption Behavior of Multipass FCA Weld Metals (다층 FCA 용착금속의 수소취성 저항성 및 확산성 수소 방출 거동)

  • Yoo, Jaeseok;Xian, Guo;Lee, Myungjin;Kim, Yongdeok;Kang, Namhyun
    • Journal of Welding and Joining
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    • v.31 no.6
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    • pp.112-118
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    • 2013
  • In this study, constant loading test (CLT) was performed to evaluate the hydrogen embrittlement resistance for multipass FCA weld metals of 600MPa tensile strength grade. The microstructures of weld metal-2 having the smallest carbon equivalent (Ceq=0.37) consisted of grain boundary ferrite and widmanstatten ferrite in the acicular ferrite matrix. The weld metal-1 having the largest Ceq=0.47, showed the microstructures of grain boundary ferrite, widmanstatten ferrite and the large amount of bainite (vol.%=19%) in the acicular ferrite matrix. The weld metal-3 having the Ceq=0.41, which was composed of grain boundary ferrite, widmanstatten ferrite, and the small amount of bainite (vol.%=9%) in the acicular ferrite matrix. Hydrogen desorption spectrometry (TDS) used to analyze the amount of diffusible hydrogen and trapping site for the hydrogen pre-charged specimens electrochemically for 24 hours. With increasing the current density of hydrogen pre-charging, the released amount of diffusible hydrogen was increased. Furthermore, as increasing carbon equivalent of weld metals, the released diffusible hydrogen was increased. The main trapping sites of diffusible hydrogen for the weld metal having a low carbon equivalent (Ceq=0.37) were grain boundaries and those of weld metals having a relatively high carbon equivalent (Ceq: 0.41~0.47) were grain boundaries and dislocation. The fracture time for the hydrogen pre-charged specimens in the constant loading test was decreased as the carbon equivalent increased from 0.37 to 0.47. This result is mainly due to the increment of bainite that is vulnerable to hydrogen embrittlement.

Evaluation of Fracture Toughness and Microstructure on FCA Weldment According to Heat Input (입열량에 따른 FCAW용접부 파괴인성에 미치는 미세조직의 영향)

  • Shin, Yong-Taek;Kang, Sung-Won;Kim, Myung-Hyun
    • Journal of Welding and Joining
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    • v.26 no.3
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    • pp.51-60
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    • 2008
  • This paper is to evaluate fracture characteristics of API 2W Gr.50 TMCP steel weldment typically applied for offshore structures, with the focus on the influence of heat input arising from flux cored arc welding. Based on the results and insights developed from this study, it is found that the toughness for both CTOD and impact exhibits a tendency to decrease as the weld heat input increases. The reheated zone of weldmetal exhibit lower hardness than solidified zone and microstructure that are liable to affect the toughness are acicular ferrite and martensite-austenite constituents (M-A). In particular, M-A is a more effective micro-phase for CTOD toughness than impact toughness.

A Study on Characteristics of Dissimilar Welds between Super Duplex Stainless Steel UNS S32750 and Carbon Steel A516-70 with FCAW (슈퍼듀플렉스 스테인리스강 UNS S32750과 탄소강 A516-70의 이종금속 FCA 용접 특성에 대한 연구)

  • Moon, In-June;Jang, Bok-Su;Kim, Se-Cheol;Koh, Jin-Hyun
    • Journal of Welding and Joining
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    • v.32 no.4
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    • pp.26-33
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    • 2014
  • The metallurgical and mechanical characteristics, toughness and corrosion resistance of dissimilar welds between super duplex stainless steel UNS S32750 and carbon steel ASTM A516Gr.70 have been evaluated. Three heat inputs of 21.12, 24.00, 26.88kJ/cm were employed to make joints of dissimilar metals with flux cored arc welding(FCAW). Based on microstructural examination, vermicular ferrite was formed in the first layer of weld at low heat input(21.12kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.61 while acicular ferrite was formed in last layer of weld at high heat input(26.88kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.72. Ferrite percentage in dissimilar welds was lowest in the first layer of weld regardless of heat inputs and it gradually increased in the second and third layers of weld. Heat affected zone showed higher hardness than the weld metal although reheated zone showed lower hardness than weld metal due to the formation of secondary austenite. Tensile strengths of dissimilar welds increased with heat input and there was 100MPa difference. The corrosion test by ferric chloride solution showed that carbon steel had poor corrosion resistance and pitting corrosion occurred in the first layer(root pass) of weld due to the presence of reheated zone where secondary austenite was formed. The salt spray test of carbon steel showed that the surface only corroded but the amount of weight loss was extremely low.

A Study of Characteristics on the Dissimilar Metals (ASTM Type 316L - Carbon Steel : ASTM A516-70) Welds Made with FCA Multiple Layer Welding (스테인리스강(ASTM Type 316L)과 탄소강(ASTM A516 Gr.70) 이종금속의 FCA 다층 용접부 특성에 대한 연구)

  • Kim, Se Cheol;Hyun, Jun Hyeok;Shin, Tae Woo;Koh, Jin Hyun
    • Journal of Welding and Joining
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    • v.34 no.3
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    • pp.69-76
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    • 2016
  • Characteristics of dissimilar metal welds between ASTM Type 316L and carbon steel ASTM A516 Gr.70 made with FCAW were evaluated in terms of microstructure, ferrite content, EDS analysis, hardness, tensile strength, impact toughness and corrosion resistance. Three heat inputs of 10.4, 16.9, 23.4kJ/cm were employed to make joints of dissimilar metals with E309LMoT1-1 wire. Microstructure of dissimilar weld metals consisted of mostly vermicular type of ${\delta}$-ferrite and some lathy type of ${\delta}$-ferrite, and ${\delta}$-ferrite was transformed into globular type in reheated zone. In all conditions, weld metals were solidified on FA solidification mode. Based on the EDS analysis of weld metals, All Creq/Nieq values were in the range of FA solidification mode, and it was decreased with increasing heat inputs whereas it was increased with increasing layers. The amount of ${\delta}$-ferrite was decreased with increasing heat input due to the difference of cooling rate, and it was increased with increasing layers. Accordingly, hardness and tensile strength of dissimilar metals weld joints was decreased with increasing heat input while impact energy was increased with increasing heat input. Corrosion test of dissimilar metals weld joints showed that weight gain rate of heat input 10.4kJ/cm was the greatest, and that of three heat inputs became constant after certain time.

Heat Treatment Effect on Pitting Corrosion of Super Duplex Stainless Steel UNS S32750 FCA Welds (슈퍼 듀플렉스 스테인리스강 UNS S32750의 FCA 용접 후 열처리가 공식에 미치는 영향)

  • Jang, Bok-Su;Moon, In-June;Kim, Se-Cheol;Koh, Jin-Hyun
    • Journal of Welding and Joining
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    • v.31 no.5
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    • pp.20-25
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    • 2013
  • This study was carried out to investigate the influence of a sigma phase precipitation on the pitting corrosion resistance and microstructural change of super duplex stainless steels(UNS S32750). The welds made by FCAW (Flux Cored Arc Welding) were heat treated ($930^{\circ}C$, $1080^{\circ}C$, $1230^{\circ}C$) and quenched. Based on the microstructural examination, it was found that the ${\sigma}$ phase was formed in base metals and welds heat treated at $930^{\circ}C$ while there were little ${\sigma}$phases formed in base metals and weld metal experienced the relatively fast cooling from $1080^{\circ}C$ and $1230^{\circ}C$. On the other hand, the most weight loss due to pitting corrosion occurred in base and weld metals heat treated at $930^{\circ}C$. It was confirmed that the pitting corrosion occurred in the phase boundaries of ferrite/sigma and austenite/sigma. The pitting corrosion resistance decreased owing to an increase in Cr, Mo depleted areas adjacent to the intermetallic phases such as ${\sigma}$phases. The hardness was greatly increased due to the precipitation ${\sigma}$phases.