• Title/Summary/Keyword: Weld Strength

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A Study on the Fatigue Strength Improvement using Weld Toe Burr Grinding (용접토우부의 그라인딩에 의한 피로강도 증대효과에 대한 연구)

  • Kang, Sung-Won;Kim, Myung-Hyun;Choi, Jae-Young;Kim, Wha-Soo;Paik, Young-Min
    • Journal of Welding and Joining
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    • v.24 no.2
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    • pp.42-47
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    • 2006
  • While it is known that the weld toe grinding method may give 3.4 times of fatigue strength improvement, this improvement may significantly vary according to weld bead shapes and loading modes. Although tremendous interest have been given in improving fatigue strength improvement for ship structures, quantitative results are yet in need. In this context, a series of fatigue tests is carried out for a type of test specimen that are typically found in ship structures. Weld burr grinding is carried out using a electric grinder in order to remove surface defects and improve the weld bead profile. The test results are compared with the same type of test specimen without applying the fatigue improvement technique in order to obtain a quantitative measure of the fatigue strength improvement. On the other hand, both hot spot stress and structural stress methods are employed to compare the effectiveness of the two methods in evaluating the fatigue strength improvement of welded structures.

Influence of Welding Shapes and Welding Procedures on Fatigue Strength of Small Diameter Branch Welded Pipe Joint (소구경 분기배관 용접부의 피로강도에 미치는 용접부 형상 및 용접공정의 영향)

  • Baek, Jong-Hyun;Kim, Cheol-Man;Kim, Woo-Sik
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.1092-1097
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    • 2003
  • S-N fatigue tests were conducted to investigate the fatigue strength of small diameter socket and butt welded joints made of carbon steels. Experimental parameters were pipe diameter, throat depth, shape of socket welds and welding procedure. Filler metals used in SMAW and GTAW procedure were E9016-G with diameter of 4.0 mm and ER70S-G with diameter of 2.4 mm. API 5L Gr.B pipes were adopted as a small diameter branch pipes. All socket fittings were machined from ASTM A105 carbon steel. Tensile strength was not affected by the welding procedure. Fatigue strength in socket weld joints increased with increasing pipe diameter, area of weld metal and weld leg length of pipe side.

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Effects of Welding Parameters on Weld Metal Strength and Recovery of Alloying Elements in FCAW (FCAW에서 용접변수에 따른 용접금속 강도 및 와이어 합금원소의 회수율 변화)

  • Jung, Dong-Hee;Bang, Kook-Soo;Park, Chan;Chang, Woong-Sung;Park, Chul-Gyu
    • Journal of Welding and Joining
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    • v.26 no.2
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    • pp.69-74
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    • 2008
  • 590MPa grade weldable steels were gas metal arc welded with flux cored wires. Welding parameters such as current, voltage, and speed were varied independently. Effects of each parameter on the strength and chemical composition of weld metal were investigated. Increase of voltage caused decrease of weld metal tensile strength due to the low recovery of alloying elements such as carbon and manganese. On the contrary, increase of current and speed resulted in increase of weld metal strength because of higher recovery of the alloying elements.

S-N Fatigue Strength of Small Diameter Branch Welded Pipe with Variation of Welding Shapes and Welding Procedures (용접부의 형상과 공정변화에 따른 소구경 분기배관의 피로강도 특성평가)

  • 백종현;김우식
    • Journal of Welding and Joining
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    • v.22 no.3
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    • pp.50-55
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    • 2004
  • S-N fatigue tests were conducted to investigate the fatigue strength of small diameter socket and butt welded joints made of carbon steels. Experimental parameters were pipe diameter, throat depth, shape of socket welds and welding procedure. Filler metals used in SMAW and GTAW procedure were E9016-G with diameter of 4.0 m and ER70S-G with diameter of 2.4 m. API 5L Gr.B pipes were adopted as a small diameter branch pipes. All socket fittings were machined from ASTM A105 carbon steel. Tensile strength was not affected by the welding procedure. Fatigue strength in socket weld joints increased with increasing pipe diameter, area of weld metal and weld leg length of pipe side.

Microstructural Characteristics of 800 MPa Grade High Strength Steel Weld Metals (800 MPa급 고강도강 용접금속의 미세조직 특성 비교 연구)

  • Lee, Jae-Hee;Kim, Sang-Hoon;Yoon, Byung-Hyun;Kim, Hwan-Tae;Kil, Sang-Cheol;Lee, Chang-Hee
    • Journal of Welding and Joining
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    • v.29 no.1
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    • pp.65-73
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    • 2011
  • Microstructural characteristics of two high strength (600 MPa & 800 MPa) weld metals produced by flux-cored arc welding process (FCAW) were evaluated. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at relatively high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 MPa grade weld metal was composed of about 85% acicular ferrite and 15% low temperature forming phases (bainite, martensite). The prior austenite grain size of 800 MPa grade weld metal was decreased by solute drag force. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by a transmission electron microscopy (TEM). In both 600 MPa and 800MPa grade weld metals, the inclusions were mainly consisted of Ti-oxide and Mn-oxide, and the average size of inclusions was $0.7{\mu}m$. The 800 MPa grade weld metal exhibited higher tensile strength and similar toughness compared with the 600 MPa grade weld metal. This result is mainly due to a higher fraction of low temperature products and a lower fraction of grain boundary ferrite in the 800 MPa grade weld metal.

Variation of Mechanical Properties according to Microstructure of High Strength Steel Weld Metal (고강도강 용접금속의 미세조직에 따른 기계적 특성 변화 연구)

  • Lee, Jae-Hee;Kim, Sang-Hoon;Yoon, Byung-Hyun;Jung, Hong-Chul;Lee, Chang-Hee
    • Proceedings of the KWS Conference
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    • 2010.05a
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    • pp.70-70
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    • 2010
  • In the present study, to estimate the mechanical properties of 800 MPa grade weld metal, welding was carried out using 800 and 600 MPa grade flux cored arc welding (FCAW) consumable and characteristics of the weld metals were investigated. The chemical composition of weld metals was investigated by an optical emission spectroscopy (OES) method. The microstructure of weld metals was analyzed by optical microscopy (OM) and secondary electron microscopy (SEM). The compositions and sizes of inclusions which are the dominant factors for the nuclei of acicular ferrite were analyzed by an transmission electron microscopy (TEM). In addition, mechanical properties of the weld metals were evaluated through tensile tests and charpy impact tests. Mostly the acicular ferrite phase which has high strength and toughness was observed. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 MPa grade weld metal was composed of about 73% acicular ferrite and 27% low temperature phase (bainite, martensite). Toughness was considerably decreased due to the increase of tensile strength (from 600 MPa to 800 MPa). The sizes of inclusions which were observed in both weld metal were $0.4{\sim}0.8\;{\mu}m$, it is effective size to form acicular ferrite.

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The Fatigue Behavior of Tailored Welded Blank Sheet Metal by Laser Beam (레이저를 이용한 Tailored Blank 용접 판재의 피로거동)

  • 오택열
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.9 no.4
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    • pp.48-55
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    • 2000
  • For the Tailor Welded Blank sheet used for automobile body panel, the characteristics of fatigue strength and crack propagation behavior were studied. The thickness of specimens was joined to be same (0.9mm+0.9mm) and different (0.9mm+2.0mm) .As a base test, mechanical properties around weld zone were examined . The results indicated that there were no significant decreases in mechanical properties , but hardness around weld bead was 2.3 times greater than base material . The fatigue strength was the highest when the loading direction was parallel to the welding direction, which was about 85% of tensile strength of base material. It was decreased by 8.5% when the thickness of specimens and base metal was different, and it was increased by 25% when pres-strain was applied. The crack propagation rate was noticeably decreased around weld line and rapidly increased as it passed through weld line. Reviewing the shape of the crack propagation , crack width around weld line was around the weld zone due to retardation of crack growth , but is became narrow passing weld line due to decreased toughness.

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The Effects of Microstructure on Cold Crack in High-Strength Weld Metals (고강도 용착금속의 미세조직이 저온균열에 미치는 영향)

  • Lee, Myung-Jin;Kang, Nam-Hyun
    • Journal of Welding and Joining
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    • v.32 no.1
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    • pp.22-27
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    • 2014
  • In the past, cold crack was commonly observed in the HAZ(heat affected zone) of high-strength steels. Applying to TMCP(thermo-mechanical controlled process) and HSLA(high strength low alloy) steels, cold crack tends to increase the occurrence in the weld metal. It is generally understood that cold crack occurs when the following factors are present simultaneously : diffusible hydrogen in the weld metal, a susceptible microstructure and residual stress. In particular, many studies investigated the microstructural effect on the cold crack in HAZ and the cold crack in weld metals starts to receive the special attendance in modern times. The purpose of the study is to review the effect of weld microstructures (grain boundary ferrite, Widm$\ddot{a}$nstatten ferrite, acicular ferrite, bainite and martensite) on cold crack in the weld metals. Among various microstructures of weld metals, acicular ferrite produced the greatest resistance to the cold crack due to the fine interlocking nature and high-angle grain boundary of the microstructure.

A Study on the Adaptive Resistance Spot Welding for High Strength Steel of 600Mpa and 1200Mpa Grade (600MPa급과 1200MPa급 고장력강의 적응 제어형 저항 점 용접에 관한 연구)

  • Lee, Yeong-Ju;Song, Yeong-Chae;Jeong, Byeong-Hun;Lee, Mun-Yong
    • Proceedings of the KWS Conference
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    • 2007.11a
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    • pp.73-75
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    • 2007
  • The resistance spot weld is among the most common automotive weld method, now a constant current type is the most common used types. A constant current type have a weak point which can not deal with a defect occurrence by external factors, and recently the adaptive resistance spot weld have been applied around the advanced automotive company. This technology can maintain a stable weld quality through a suitable control the current and weld time with weld environment. In this research, the adaptive resistance spot weld is applied to high strength steels, and its application possibility and weld characteristics are presented.

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High Fatigue Life and Tensile Strength Characteristics of Low Activation Ferritic Steel(JLE-1) by TIG Welding (TIG용접한 저방사화 페라이트강(JLF-1)의 고온강도 및 피로수명특성)

  • Yoon, H.K.;Lee, S.P.;Kim, S.W.;Park, W.J.;Kohyama, A.
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.181-186
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    • 2001
  • JLF-1 steel (Fe-9Cr-2W-V-Ta), low activation ferritic steel, is one of the promising candidate materials fer fusion reactor applications. High temperature fatigue life and tensile strength of JLF-1 steel and its TIG welded joints were investigated at the room temperature and $400^{\circ}C$. The strength of base metal (JLF-1) is in between those of weld metal and the HAZ. When the test temperature was increased from room temperature to $400^{\circ}C$, both strength and ductility decreased for base metal, weld metal and the HAZ. The longitudinal specimens of base metal showed similar strength and ductility compared with those of the transverse specimens at room temperature and $400^{\circ}C$. Little anisotropy was observed in the JLF-1 steel base metal in terms of rolling direction. Fatigue limit of weld metal which was obtained from cross-weld specimen is 495MPa. Thus, the weld metal showed the higher fatigue limit than those of base metal at both room temperature and $400^{\circ}C$. Little anisotropy of fatigue properties was observed for JLF-1 base metal in terms of rolling direction. When the test temperature was increased from room temperature to $400^{\circ}C$, the fatigue limit of both base metal and weld metal decreased substantially.

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