• Title/Summary/Keyword: Heat Input

Search Result 1,095, Processing Time 0.023 seconds

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
    • /
    • v.29 no.2
    • /
    • pp.97-105
    • /
    • 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.

Evaluation of Underclad Crack Susceptibility of the SA508 Class 3 Steel for Pressure Vessels -Optimization of Heat Input- (압력용기용 SA508 class3강에 대한 underclad 균열의 감수성 평가 - 입열량의 최적화)

  • 김석원;양성호;김준구;이영호
    • Journal of Welding and Joining
    • /
    • v.13 no.2
    • /
    • pp.139-149
    • /
    • 1995
  • Many pressure vessels for the power plants are fabricated from low alloy ferritic steels. The inner sides of the pressure vessels are commonly weld_cladded with austenitic stainless steels to minimize problems of corrosive attack. The submerged-arc welding(SAW) process is now used in preference to other processes because of the possibilities open to automation to reduce the overaII welding times. The most reliable way to avoid underclad cracks(UCC) which are often detected at the overlap of the clad beads is to use nonsusceptible steels such as SA508 class 3. At present domestically developed forging steel of SA508 cl.S is now being cladded with single layer by using 90mm wide strip, which transfers higher heat input into the base metal compared to the conventional two layers strip cladding which has been in wide use with 30-60 mm wide strip. But the current indices for the influence of heat input on crack susceptibility are not accurate enough to express the subtle difference in crack susceptibility of the steel. Therefore, the purpose of this present study is: l) To determine UCC susceptibility on domestic forging steel, SA508 cl.S cladded with single layer by using submerged arc 90mm strip and, 2) To optimize heat input range by which the crack susceptibility could be eliminated.

  • PDF

A Study on Microstructure and Thoughness of Electrogas Weldments (일렉트로가스 용접부의 조직 및 인성에 관한 연구)

  • 이해우;장태원;이윤수;석한길;강성원
    • Journal of Welding and Joining
    • /
    • v.14 no.1
    • /
    • pp.68-74
    • /
    • 1996
  • The microstructure of HAZ and the mechanical properties in weldments such as hardness and toughness were studied for mild steel and AH36 grade TMCP steel, as increasing heat input with electrogas welding process. The results of this study can be summarized as follow: 1) In the HAZ of mild steel, the width of coarse grained zone was larger than that of the nomalized zone, however in the case of TMCP steel, the nomalized zone was wider than the coarse grained zone. 2) The grain size of HAZ become coarse with increasing heat input. And at the same heat input, the grain size of TMCP steel was more coarser than that of mild steel. 3) According to the change of heat input, the deviation of hardness values was not significant, and the maximum values of hardness was not in HAZ but in the weld metal. And the hardness values in root part was higher than in face part. 4) Even though the HAZ grain size of mild steel was larger than that of TMCP steel, the impact values for mild steel was higher than those for TMCP steel, and the impact values in face part was higher than those in root part.

  • PDF

Effect of Heat Input on the Mechanical Properties of SA508 class 3 Steel Weldments with Submerged Arc Welding (SA508 class 3 서브머지드 아크용접부의 기계적 성질에 미치는 입열량의 영향)

  • Seo Yun-seok;Koh Jin-Hyun;Kim Nam-Hoon;Oh Se-Yong;Choo Kee-Nam
    • Journal of Welding and Joining
    • /
    • v.22 no.5
    • /
    • pp.38-45
    • /
    • 2004
  • The present study is to investigate the effect of heat input on the microstructure, tensile properties and toughness of single-pass submerged arc bead-in-groove welds produced on SA508 class 3 steels. The heat input was varied in the range of 1.6, 3.2 and 5.0 kJ/mm. The toughness of weld metals was evaluated by using subsize Charpy V-notch specimens in the temperature range of -19$0^{\circ}C$ to 2$0^{\circ}C$. The weld microstructure and fractography were observed by optical and scanning electron microscopies, respectively. With increasing heat inputs, tensile strength and hardness of weld metals were decreased while elongation was increased. The poor notch toughness at 1.6 kJ/mm was attributed to the formation of ferrite with aligned second phase and banitic microstructure with high yield strength while that at 5.0 kJ/mm was due to the presence of grain boundary and polygonal ferrites. The microstructure of the intermediate energy input welds consisted of a high proportion of acicular ferrite with limited polygonal ferrites, which provide improved notch toughness.

The characteristics of bead welding on steel with process parameter during the laser-arc hybrid welding(II) - Effect of heat input parameters - (강의 레이저-아크 하이브리드 용접시 공정변수에 따른 비드용접특성 (II) - 용접 입열 변수의 영향 -)

  • Kim, Jond-Do;Myung, Gi-Hoon;Park, In-Duck
    • Journal of Welding and Joining
    • /
    • v.33 no.2
    • /
    • pp.91-96
    • /
    • 2015
  • The laser-arc hybrid welding of SS400 steel was carried out with the use of disk laser equipment of 6.6kW maximum power and MAG equipment of pulse mode. Parameter regarding heat input is one of the most important factors that directly affect penetration characteristics and welding defect. Therefore in this study, the effects of laser power, welding speed and current, voltage and pulse correction were investigated. As experiment result, it was found that the lower heat input, the more likely humping bead is formed at the back, and such humping bead could be suppressed by increasing laser power and arc current or decreasing welding speed, thus increasing heat input. Also deep penetration could be achieved by reducing arc voltage or pulse correction parameter in the same welding condition.

Influence of Heat Input and Weld Bead Composition on Welding Property in the Laser Welding between Sintered Segment and Mild Steel Shank (소결체와 저탄소강의 레이저용접 특성에 미치는 입열량 및 용접부 성분변화의 영향)

  • Jung Woo-Gwang;Cho Nam-Joon;Kim Sung-Wook;Lee Chang-Hee;Kim Sung-Dea;Lee Joo-Hyung;Park Hwa-Soo
    • Korean Journal of Materials Research
    • /
    • v.14 no.6
    • /
    • pp.425-431
    • /
    • 2004
  • A laser welding was applied between sintered tip of Fe-Co-W and low carbon steel shank for the diamond saw blade. The welding characteristics and formation of defects were investigated carefully for the weld fusion zone in different welding condition. Dendrite arm spacing in weld bead decreased with decrease of heat input. Co and W increased and Fe decreased in the weld fusion zone with increase of the heat input. The corresponding change of composition was observed with the change of beam position. The maximum and total length of crack decreased with increase of the heat input. The crack in weld bead was propagated along the dendrite boundary and was caused mainly by the segregation of constituent during the solidification.

Mechanical properties of fine grained steel weldments formed with low heat input (세립강 저입열 용접부의 기계적 성질)

  • 윤중근;박태동;김광수;박영수
    • Proceedings of the KWS Conference
    • /
    • 2003.11a
    • /
    • pp.227-229
    • /
    • 2003
  • Low heat input welding methods have been investigated in order to minimize the HAZ softening of the 600MPa grade fine grained steel weldment. The welding processes of interest were a high speed FCA welding with a multi-torch welding system, laser welding with filler feeding and hybrid laser welding. No HAZ softening was found for all the weldments formed with low heat input less than 10kJ/cm. Tensile strength of the weldments was high enough to satisfy the required value. Impact toughness of the weldments was also good even at -20$^{\circ}C$.

  • PDF

An observer design for the superheater temperature estimation (과열기의 온도추정을 위한 관측기의 구성)

  • 서진헌;황재호;이상혁
    • 제어로봇시스템학회:학술대회논문집
    • /
    • 1990.10a
    • /
    • pp.101-106
    • /
    • 1990
  • The problem of constructing an observer for use in the control of superheater temperature with desuperheater is considered. The distributed heat input into the superheater is usually not available for use in the observer, and hence is treated as a disturbance. The observer theory for systems with unknown inputs is exploited and applied to the problem. Approximation of the heat input utilizing the specific heat input distribution pattern is also considered.

  • PDF

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
    • /
    • 2005.11a
    • /
    • pp.162-164
    • /
    • 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.

  • PDF

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
    • /
    • v.26 no.3
    • /
    • pp.51-60
    • /
    • 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.