• Title, Summary, Keyword: Heat Input

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A STUDY ON THE FORMATION OF IMPERFECTIONS IN CW $CO_2$ LASER WELD OF DIAMOND SAW BLADE

  • Minhyo Shin;Lee, Changhee;Kim, Taiwoung;Park, Heedong
    • Proceedings of the KWS Conference
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    • pp.639-643
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    • 2002
  • The main purpose of this study was to investigate the formation mechanisms of imperfections such as irregular humps, outer cavity and inner cavity in the laser fusion zone of diamond saw blade. Laser beam welding was conducted to join two parts of blade; mild steel shank and Fe-Co-Ni sintered tip. The variables were beam power and travel speed. The microstructure and elements distributions of specimens were analyzed with SEM, AES, EPMA and so on. It was found that these imperfections were responded to heat input. Irregular humps were reduced in 10.4∼17.6kJ/m heat input range. However there were no clear evidences, which could explain the relations between humps formation and heat input. The number of outer cavity and inner cavity decreased as heat input was increased. Considering both possible defects formations mechanisms, it could be thought that outer cavity was caused by insufficient refill of keyhole, which was from rapid solidification of molten metal and fast molten metal flow to the rear keyhole wall at low heat input. More inner cavities were found near the interface of the fusion zone and sintered segment and in the bottom of the fusion zone. Inner cavity was mainly formed in the upper fusion zone at high heat input whereas was in the bottom at low heat input. Inner cavity was from trapping of coarsened preexist pores in the sintered tip and metal vapor due to rapid solidification of molten metal before the bubbles escaped.

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A Study on Tensile Properties and HAZ Softening Depending on the Amount of Heat Input in MIG Welding of Al6082-T6 (Al6082-T6의 MIG용접부에서 입열량에 따른 열영향부의 연화와 인장특성에 관한 연구)

  • Baek, Sang-Yeob;Park, Kyung-Do;Kim, Won-Il;Cho, Sang-Myung
    • Journal of Welding and Joining
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    • v.29 no.1
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    • pp.59-64
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    • 2011
  • Al6082-T6 is widely used because of its corrosion resistance and excellent strength. HAZ softening occurs in MIG welding process for this aluminium alloys because this aluminium alloy is heated to higher temperature than its aging temperature during welding. Therefore, low heat input and minimum standard deviation of heat input are required for narrow HAZ width and, for higher strength of welds. In this study, Al6082-T6 was used to examine for HAZ softening with various heat input in aluminium MIG welding. For weldments, micro hardness was measured and tensile test was carried out. Minimum hardness was increased at high speed welding such as 80cm/min and 120cm/min in welding speed comparing with 40cm/min. Also, in case of high speed welding such as 80cm/min and 120cm/min, tensile strength of weldments was increased about 10% comparing with low speed welding(40cm/min).

Performance Analysis of Thermosphon Using Phase Change Material (상변화 물질을 이용한 열사이폰의 성능 분석)

  • Paek, Yee;Cho, Ki-Hyon;Lee, Joo-Seong
    • Journal of the Korean Society of Industry Convergence
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    • v.3 no.3
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    • pp.219-228
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    • 2000
  • In order to evaluate the applicability of thermosyphon as an equipment of heat transfer to the case where natural of low temperature and low density is necessary and to propose the possibility of using natural energy being clean and inexhaustible, a thermosypon using methanol as working fluid was constructed and its transfer characteristics were analysed. The wall temperature of the thermosyphon was maintained relatively uniform after rapid increase until after being heated about ten minutes regardless of the level of input powers to the evaporating section. Inner pressure of the thermosyphon increased rapidly until after ten minutes, and then increased slowly depending on the level of input power. But heat transfer coefficient of the condensible section decreased in inverse proportion to input powers of 250~300W, showing $1008.3{\sim}829.8W/m^2{\cdot}^{\circ}C$. For the input powers of the thermosyphon within the range of 100~250W, heat transferred and heat flux increased relatively linearly showing, in the case of input powers of 250~300W, heat transfer efficiency considerable increased, showing 63.8%.

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IMPROVEMENT OF GAS TUNGSTEN ARC WELDABILITY FOR FERRlTIC STAINLESS STEELS

  • Cui Li;Jeong, Ho-shin;Park, Byung-Il;Kim, Sung-Kab
    • Proceedings of the KWS Conference
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    • pp.107-112
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    • 2002
  • Ferritic stainless steels would be the most important alloys under the chloride environment. They are a cheaper alternative to austenitic stainless steels [1]. The present study is related to gas tungsten arc welding (GTAW) characteristics of Type 444 stainless steels. The heat of welding leads to grain coarsening in the HAZ and in the weld metal of ferritic stainless steels because they solidify directly from the liquid to the ferritc phase without any intermediate phase transformation. It is therefore recommended that these alloys be welded with a low heat input and at high welding speeds. Attempts to improve weldability were made by using of direct current straight polarity (DCSP) and pulsed current GTAW processes in this study. Measuring weld bead, grain size and Erichsen test were performed and the effects of heat input, pulse frequency on the weld metal and HAZ were studied. The main results were obtained as followings: decreasing heat input was effective to control the width of weld both in DCSP welding and in pulsed current welding; pulsed current welding was found to refine the grain size effectively and the finest grain size was found at the frequency of 150Hz in pulsed current welding; it was found that decreasing heat input also refine the HAZs effectively and the frequency had no different effect on HAZ at the same heat input; the ductility could be improved effectively in pulsed current welding.

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Microstructure Evolution and Its Effect on Strength during Thermo-mechanical Cycling in the Weld Coarse-grained Heat-affected Zone of Ti-Nb Added HSLA Steel (Ti-Nb첨가 저합금강 용접열영향부에서의 열-응력 이력이 미세조직 및 기계적 성질에 미치는 영향에 관한 연구)

  • Moon, Joonoh;Lee, Changhee
    • Journal of Welding and Joining
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    • v.31 no.6
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    • pp.44-49
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    • 2013
  • The influence of thermo-mechanical cycling on the microstructure and strength in the weld coarse-grained heat affected zone (CGHAZ) of Ti-Nb added low carbon HSLA steel was explored through Vickers hardness tests, nanoindentation experiments, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Undeformed and deformed CGHAZs were simulated using Gleeble simulator with different heat inputs of 30kJ/cm and 300kJ/cm. At high heat input of 300kJ/cm, the CGHAZ consisted of ferrite and pearlite and then their grain sizes were not affected by deformation. At low heat input of 30kJ/cm, the CGHAZ consisted of lath martensite and then the sizes of prior austenite grain, packet and lath width decreased with deformation. In addition, the fraction of particle increased with deformation and this is because the precipitation kinetics was accelerated by deformation. Meanwhile, the Vickers and nanoindentation hardness of deformed CGHAZ with 30kJ/cm heat input were higher than those of undeformed CGHAZ, which are due to the effect of grain refinement and precipitation strengthening.

A Study on Welding Distortion of Channel I Butt SA Weld using FE Analysis (유한요소해석을 이용한 Channel I butt SA 용접부 변형 해석에 관한 연구)

  • Shin, Dae-Hee;Shin, Sang-Beam;Lee, Joo-Sung
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • pp.189-192
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    • 2006
  • The purpose of this study is to evaluate the welding distortion at the channel I butt SA weldment. In order to do it, the heat input model for the weldment was defined as combined heat source with the surface heat flux of gaussian mode and volume heat source uniformly distributed within weld groove on the basis of comparing the shapes of molten pool and temperature distribution obtained by FEA and experiment. The arc efficiency of SA welding for 2 dimensional FE analysis was determined as 0.85. The results of welding distortions at the weldment obtained by FEA and heat input conditions proposed have a good agreement with those obtained by experiment. Based on the results, it was suggested that the proper heat input model should be required to evaluate the welding distortion for weldment.

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A Study on the Prediction of Welding Distortion and Residual Stress for Channel I Butt SA Weldment Using FE Analysis (유한요소해석을 이용한 채널 I 형 잠호 맞대기 용접부의 변형 및 잔류 응력 예측에 관한 연구)

  • Shin, Dae-Hee;Shin, Sang-Beom;Lee, Joo-Sung
    • Journal of the Society of Naval Architects of Korea
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    • v.44 no.6
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    • pp.598-604
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    • 2007
  • The purpose of this study is to establish the predictive method of welding distortion and residual stress for the channel I butt SA (submerged arc) weldment using FEA. In order to do it, the heat input model for the weldment was defined as the combined heat source with the surface heat flux of gaussian distribution and volumetric heat source uniformly distributed within weld groove by comparing the shapes of molten pool and temperature distribution obtained by FEA with those of experiments. The arc efficiency of SA welding for two-dimensional FE analysis was evaluated as 0.85. The welding distortion and residual stress of the weldment obtained by FEA and heat input model proposed have a good agreement with those obtained by experiment. Based on the results, it was suggested that the proper heat input model should be required to evaluate the welding distortion for weldment.

Analytical Study of heat Transfer in Evaporative Cooling of a Porous Layer (다공층의 증발냉각 열전달에 관한 해석적 연구)

  • 김홍제;이진호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.1
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    • pp.104-111
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    • 1992
  • In this study, the heat transfer characteristics of the evaporative transpiration cooled system is analytically investigated considering the occurrence of the two-phase evaporation zone. Under the condition of the external heat input, analytical solutions of the three regions (i.e., vapor, liquid and two-phase evaporation zone) are respectively obtained using the matching conditions for the steady-state problem where properties are constant. As results, the length of the evaporation zone increases with increasing heat input and with decreasing mass flow rate. It also increases with increasing particle size, system porosity, thermal conductivity of material, inlet temperature and latent heat of coolant. The position of the lower interface of the evaporation zone have a lot of efforts on the evaporation zone length, the position of the upper interface penetrates deeper into the porous layer with lower thermal conductivity of porous material, higher system porosity and larger particle size.

Effects of TiN and B on Grain Refinement of HAZ Microstructure and Improvement of Mechanical Properties of High-strength Structural Steel Under High Heat Input Welding (고강도 구조용 철강소재의 대입열 용접 시 열영향부의 조직 미세화 및 기계적 특성 향상에 미치는 TiN 및 B의 효과)

  • Park, Jin-seong;Hwang, Joong-Ki;Cho, Jae Young;Han, Il Wook;Lee, Man Jae;Kim, Sung Jin
    • Korean Journal of Materials Research
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    • v.29 no.2
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    • pp.97-105
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    • 2019
  • In the current steel structures of high-rise buildings, high heat input welding techniques are used to improve productivity in the construction industry. Under the high heat input welding, however, the microstructures of the weld metal (WM) and heat-affected zone (HAZ) coarsen, resulting in the deterioration of impact toughness. This study focuses mainly on the effects of fine TiN precipitates dispersed in steel plates and B addition in welding materials on grain refinement of the HAZ microstructure under submerged arc welding (SAW) with a high heat input of 200 kJ/cm. The study reveals that, different from that in conventional steel, the ${\gamma}$ grain coarsening is notably retarded in the coarse grain HAZ (CGHAZ) of a newly developed steel with TiN precipitates below 70 nm in size even under the high heat input welding, and the refinement of HAZ microstructure is confirmed to have improved impact toughness. Furthermore, energy dispersive spectroscopy (EDS) and secondary-ion mass spectrometry (SIMS) analyses demonstrate that B is was identified at the interface of TiN in CGHAZ. It is likely that B atoms in the WM are diffused to CGHAZ and are segregated at the outer part of undissolved TiN, which contributes partly to a further grain refinement, and consequently, improved mechanical properties are achieved.

Effects of Heat Input and Interpass Temperature on the Strength and Toughness of Multipass Weld Metal (철골 다층 용접금속 강도 및 인성에 미치는 입열 및 패스간 온도의 영향)

  • Byeon, Ji-Cheol;Bang, Guk-Su;Jang, Ung-Seong;Park, Cheol-Gyu;Jeong, U-Hyeon
    • Proceedings of the KWS Conference
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    • pp.162-164
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    • 2005
  • 570MPa grade weldable steels were $CO_{2}$ welded with various heat input and interpass temperature using flux cored wires. Effects of heat input and interpass temperature on the strength and toughness of weld metal were investigated and interpreted in terms of microstructural change, recovery of alloying elements, and the amount of reheated weld metal.

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