• Title/Summary/Keyword: high Heat Input Welding

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Fatigue properties of welded joints for TMCP steels (TMCP 고장력강 용접부의 피로 특성에 관한 연구)

  • 임채범;권영각;엄기원
    • Journal of Welding and Joining
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    • v.8 no.2
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    • pp.40-52
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    • 1990
  • Fatigue behavior of the AH, DH and EH grade TMCP(Thermo-Mechanical Control Process) steels was studied. High cycle and low cycle fatigue tests were carried out for the weldment and base metal of each steel. The results showed that the fatigue limit at 2 * $10^6$ cycles was 33 to 37 kg/$mm^2$ for the base metal and 30 to 34 kg/$mm^2$ for the weldment. The ratio of fatigue limit to tensile strength for TMCP steels was 0.65 to 0.71, which was a value close to the upper limit for the ordinary steels. It was also found that the high cycle fatigue behavior of TMCP steels could be affected by the microstructures of base metal. It will be necessary to have fine structure for TMCP steels to increase the fatigue resistance. In low cycle fatigue test, the fatigue lifetime of AH and DH steels accorded well with the ASME best fit curve, while that of EH steel was considerably lower than the fatigue lifetime of the other steels. Fatigue resistance of the weldment made by high heat input(180kJ/cm) welding was not lower than that made by low heat input(80kJ/cm) welding in case of high cycle fatigue, but the high heat input welding decreased the fatigue resistance in case of low cycle fatigue.

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The Effects of δ-ferrite on Weldment of 9-12% Cr Steels (9-12% Cr강의 용접부에 미치는 δ-ferrite의 영향)

  • Ahn, Sung-Yong;Kang, Namhyun
    • Journal of Welding and Joining
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    • v.31 no.6
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    • pp.8-16
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    • 2013
  • As the energy consumption increases rapidly, power generation needs the high energy efficiency continuously. To achieve the high efficiency of power generation, the materials used have to endure the higher temperature and pressure. The 9-12%Cr steels possess good mechanical properties, corrosion resistance, and creep strength in high temperature due to high Cr contents. Therefore, the 9-12%Cr steels are widely used for the high-temperature components in power plants. Even though the steels usually have a fully martensitic microstructure, they are susceptible to the formation of ${\delta}$-ferrite specifically during the welding process. The formation of ${\delta}$-ferrite has several detrimental effects on creep, ductility and toughness. Therefore, it is necessary to avoid its formation. As the volume fraction of ${\delta}$-ferrite is less than 2% in microstructure, it has the isolated island morphology and causes no significant degradation on mechanical properties. For ${\delta}$-ferrite above 2%, it has a polygonal shape affecting the detrimental influence on the mechanical properties. The formation of ${\delta}$-ferrite is affected by two factors: a chemical composition and a welding heat input. The most effective ways to get a fully martensite microstructure are to reduce the chromium equivalent less than 13.5, to keep the difference between the chromium and nickel equivalent less than 8, and to reduce the welding heat input.

A Study on the Process of Hybrid Welding Using Pulsed Nd:YAG Laser and Dip-transfer DC GMA Heat Sources (펄스형 Nd:YAG 레이저와 단락이행모드의 직류 GMA 열원을 이용한 하이브리드 용접 공정에 대한 연구)

  • Cho, Won-Ik;Na, Suck-Joo
    • Journal of Welding and Joining
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    • v.25 no.6
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    • pp.71-77
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    • 2007
  • Until now, many researches on laser-arc hybrid welding processes have been conducted mainly for high power CW laser and high direct current arc to weld the thick steel plates for shipbuilding. Recently, however the usage of thin steel plates, which tend to be deformed easily by thermal energy, is been increasing because of demand of light structure such as car body in the automobile industry. Accordingly, heat sources having relatively low heat input such as pulsed laser, dip-transfer DC GMA and pulsed GMA seem to be applied more increasingly and the study about those heat sources is needed more intensively. Any heat source mentioned above can not stand alone without weld defects at a relatively high welding speed for increasing the welding productivity. This is main reason to apply the hybrid welding process which uses pulsed laser and low-heat-input GMA heat sources simultaneously to weld the thin steel plate. In this study, parameters of pulsed laser and dip-transfer DC GMA welding are studied firstly through preliminary experiments, and then analyzed in the viewpoint of their physical phenomena. Before conducting the hybrid welding, a pulse control technique is developed based on the parallel port communication and Visual C++ 6.0. Owing to development of this technique, interactions of laser and arc pulses can be controlled consistently. Using the pulse control technique, the hybrid welding is conducted and then its interactive welding phenomenon is analyzed.

Characteristic and Measurement Technology of Inner Welding Residual Stresses in Thick Steel Structures (극후물재 용접부 내부잔류응력 측정기술 및 특성)

  • Park, Jeong-ung;An, Gyu-baek;Woo, Wanchuck
    • Journal of Welding and Joining
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    • v.34 no.2
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    • pp.16-21
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    • 2016
  • Recent keywords of the heavy industries are large-scale structure and productivity. Especially, the sizes of the commercial vessels and the offshore structures have been gradually increased to deliver goods and explore or produce oil and natural gas in the Arctic. High heat input welding processes such as electro gas welding (EGW) have been widely used for welding thick steel plates with flux-cored arc welding (FCAW), especially in the shipbuilding industries. Because high heat input welding may cause the detrimental effects on the fracture toughness of the welded joint and the heat affected zone, it is essential to obtain the sufficient toughness of welded joint. There are well known that the fracture toughness like CTOD, CVN, and KIC were very important factors in order to secure the safety of the structures. Furthermore, the welding residual stress should be considered to estimate the unstable fracture in both EGW and FCAW. However, there are no references on the welding residual stress distribution of EGW and FCAW with thick steel plates. Therefore the welding residual stresses were very important elements to evaluate the safety of the welded structure. Based on the measurement results, the characteristics of residual stress distribution through thickness were compared between one-pass electron gas welding and multi-pass flux-cored arc welding. The longitudinal residual stress in the multi-pass flux-cored arc welding is tensile through all thicknesses in the welding fusion zone. Meanwhile, longitudinal residual stress of EGW is tensile on both surfaces and compressive at the inside of the plate. The magnitude of residual stresses by electron gas welding is lower than that by flux-cored arc welding.

High Productive Welding Technologies for Large Container Ship (대형 컨테이너선 건조를 위한 고능률 용접기술)

  • Goo, Yeon-Baeg;Sung, Hee-Joon;Choi, Kee-Young;Kim, Kyeong-Ju
    • Special Issue of the Society of Naval Architects of Korea
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    • 2009.09a
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    • pp.80-86
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    • 2009
  • In order to improve productivity of large container ship construction, large heat input and/or high productive welding technologies are necessary. This can be achieved by the joint research and cooperation among steel maker, welding consumable company, welding equipment company and ship yards. Two electrodes SAW process is effective the plate butt welding and partial joint welding, while FGB welding process is for the connection of block to block joint. The higher strength and thicker steel is developed, the more reliable welding procedure such as two electrodes EGW including light weight welding equipment should be developed.

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Verification of Quantitative Evaluation Method for Ferritic Weld Metal Microstructure (철강 용착금속 미세조직의 정량화 기법 검증)

  • Kim Ka-Hee;Kim Hee-Jin;Ryoo Hoi-Soo
    • Journal of Welding and Joining
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    • v.23 no.4
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    • pp.27-33
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    • 2005
  • Quantitative evaluation was performed on the microstructure of flux-cored arc(FCA) weld metal using a method blown as IIW scheme. It was mainly intended to figure out any practical difficulties in applying this method and also to provide the consumable makers with basic guide line in developing FCA welding consumables far better properties. Assessment of the experimental results showed IIW scheme was quite reliable in the low heat input range where the acicular ferrite was a major constituent. However, in the high heat input range, some scatter was noticed as the other phases like grain boundary ferrite and Widmansttaten ferrite become dominant. It implies that the accuracy of IIW scheme depends on the faction of microstructural constituents and it become worse as the fraction of latter two phases increases. This tendency was discussed in terms of the characteristics of those two phases. In addition, base line microstructure of rutile type FCA weld metal was addressed for developing new FCA welding consumables intended for higher heat input welding.

Laser weldability and mechanical behavior of hot rolled steels for hydroforming applications (하이드로포밍용 열연강재의 레이저 용접성 및 기계적 특성)

  • 이원범;이종봉
    • Proceedings of the KWS Conference
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    • 2003.05a
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    • pp.84-86
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    • 2003
  • The laser welding and its analysis of thin-sheet carbon steels were carried out with high power CO$_2$1aser. Bead on plate welding of thin sheet was examined to investigate the effect of weld variables of laser welding, and to obtain optimum welding condition. Butt-welding was also carried out to show the effect of gap on the laser weldability of thin sheet. At high welding speed, the partial penetration was obtained by low heat input. Otherwise, porosity was formed in the bead at low weld speed because of too many heat input. The maximum gap tolerance on laser welding was observed to be about 0.2mm. This gap size has good relationship with beam size of laser spot(about 0.3mm). The formability of welded sheet was about 80% value of base metal and the gap size has not affected on the formability, although weld quality is dependent on the gap size.

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A Study on Corrosion Fatigue Properties of Welded Joints for TMCP High Strength Steels (TMCP 고장력강 용접부의 부식도영 특성에 관한 연구)

  • 이택순;이휘원;김영철
    • Journal of Ocean Engineering and Technology
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    • v.10 no.3
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    • pp.14-23
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    • 1996
  • The corrosion fatigue test were carried out to evaluate the fatigue characteristics of accelerated cooled (ACC) TMCP high tensile strength steels and weld joint with high heat input by one side one run submerged are welding. In this paper, the fatigue crack growth behaviors were investigated with the center crack tension specimen of base metal and heat affected zone in substitute sea water and air, respectively Main results obtained are sunnarized as follows: 1. The fatigue crack growth rates in sea water faster than those in air environment for the different heat input values, crack growth rate of base metal is very fast and effect of heat input is not remarkable. 2. In HAZ (82kJ/cm, 116kJ/cm), the crack branching phenomena were observed in both air and sea water environment, 3. In SEM observation, the corrosion effect on base metal was larger than that on HAZ in corrosion environment.

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Lab Weldability of Pure Titanium by Nd:YAG Laser (Nd:YAG 레이저를 이용한 순티타늄판의 겹치기 용접성)

  • Kim, Jong-Do;Kwak, Myung-Sub
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.2
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    • pp.315-322
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    • 2008
  • Titanium and its alloys have excellent corrosion resistance, high strength to weight ratios and creep properties in high temperature, which make them using many various fields of application. Especially, pure titanium, which has outstanding resistance for the stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion, brings out to the best material for the heat exchanger, ballast tank, desalination facilities, and so on. Responding to these needs, welding processes for titanium are also being used GTAW, GMAW, PAW, EBW, LBW, resistance welding and diffusion bonding, etc. However, titanium is very active and highly susceptible to embrittlement by oxygen, nitrogen, hydrogen and carbon at high temperature, so it needs to shield the weld metal from the air and these gases during welding by non-active gas. In this study, it was possible to get sound beads without humping and spatter with a decrease of peak power according to increase of pulse width, change of welding speed and overlap rate for heat input control, and shield conditions at pulsed laser welding of titanium plates for Lap welding.

Development of laser tailored blank weld quality monitoring system (레이저 테일러드 블랭크 용접 품질 모니터링 시스템 개발)

  • 박현성;이세헌
    • Laser Solutions
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    • v.3 no.2
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    • pp.53-61
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    • 2000
  • On the laser weld production line, a slight alteration of the welding condition produces many defects. The defects are monitored in real time, in order to prevent continuous occurrence of defects, reduce the loss of material, and guarantee good quality. The measurement system is produced by using three photo-diodes for detection of the plasma and spatter signal in CO$_2$ laser welding. For high speed CO$_2$ laser welding, laser tailored welded blanks for example, on-line weld quality monitoring system was developed by using fuzzy multi-feature pattern recognition. Weld qualities were classified optimal heat input, a little low heat input, low heat input, and focus misalignment, and final weld quality were classified good and bad.

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