• Title/Summary/Keyword: Weld Metal HAZ

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A Study on Effect of PWHT in AH36-TMCP Steel (AH36-TMCP강의 용접후열처리 효과에 관한 연구)

  • 유효선;장원상;안병국;정세희
    • Journal of Welding and Joining
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    • v.16 no.6
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    • pp.44-51
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    • 1998
  • It is well known that the fine bainitic microstructure obtained by TMCP(thermo-mechanical control process) secures the high toughness of base metal. Besides, TMCP steel is very suitable for high heat input in welding as it has low carbon equivalent. In HAZ, however, the accelerated cooling effect imparted on the matrix by the weld thermal cycles is relieved and thus the weldment of TMCP steel has softening zone which shows low fracture toughness compared with base metal. Therefore, PHWT of weldment is carried out to improve the fracture toughness in weldment of TMCP steel which has softening zone. In this study, the effects of PWHT on the weldment of AH36-TMCP steel are investigated by the small punch (SP) test. From the several results such as SP energy and displacement at room temperature, the behavior of transition curves, the fracture strength at -196$^{\circ}C$, distribution of (DBTT)sp and (DBTT)sp, the PWHT condition of A.C. after 85$0^{\circ}C$-1 sec W.C. was suitable condition for recovering a softening zone of HAZ as welded.

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A Study on the Corrosion Rehavior and Mechanical Property by SSRTTest of Welding Part of RE36 Steel for Marine Structure (해양구조물 RE36강의 용접부 부식거동 및 SSRT법에 의한 기계적 특성에 관한 연구)

  • 김종성;김진경;김종호;이명훈;김영식;문경만
    • Journal of Advanced Marine Engineering and Technology
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    • v.24 no.4
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    • pp.460-469
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    • 2000
  • A study on the corrosion behavior of RE36 steel for marine structure was investigated with parameters such as micro-Vickers hardness, corrosion potential and corrosion current density measurement of weld metal(WM), base metal (BM) and heat affected zone(HAZ), Al anode generating current and Al anode weight loss quantity in case of cathodic protection. And we carried out slow strain rate test(SSRT) in order to research mechanical properties such as stress at maximum load, percent strain, time to fracture and strain to failure ratio etc and to find out limiting cathodic polarization potential for hydrogen embrittlement with applied cathodic polarization potential. Hardness of HAZ part was the highest among those three parts and also galvanic corrosion susceptibility was the highest in HAZ part among those three parts due to the lowest corrosion potential than other parts. However corrosion current density was the highest in WM part among those three parts. And the optimum cathodic polarization potential showing the best mechanical properties obtained by SSRT method with applied constant cathodic potential was from - 770mV to - 875mV(SCE). However it is suggested that limiting cathodic polarization potential indicating hydrogen embrittlement on the mechanical properties was under - 900mV(SCE).

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Statistical Distribution of Fatigue Crack Growth Rate for Friction Stir Welded Joints of Al7075-T651 (Al7075-T651의 마찰교반용접된 접합부의 피로균열전파율의 통계적 분포)

  • Ahn, Seok-Hwan;Kim, Seon-Jin
    • Journal of Power System Engineering
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    • v.17 no.4
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    • pp.86-93
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    • 2013
  • This paper deals with the effects of driving force and material properties on statistical distribution of fatigue crack growth rate (FCGR) for the friction stir welded joints of Al 7075-T651 aluminum plate. In this work, the statistical probability distribution of fatigue crack growth rate was analyzed by using our previous constant stress intensity factor range controlled fatigue crack growth test data. As far as this study are concerned, the statistical probability distribution of fatigue crack growth rate for the friction stir welded (FSWed) joints was found to evaluate the variability of fatigue crack growth rate for base metal (BM), heat affected zone (HAZ) and weld metal (WM) specimens. The probability distribution of fatigue crack growth rate for FSWed joints was found to follow well log-normal distribution. The shape parameter of BM and HAZ was decreased with increasing the driving force, however, the shape parameter of WM was decreased and increased with increasing the driving force. The scale parameter of BM, HAZ and WM was increased with the driving force.

Comparative Study on the Weldability of Different Shipbuilding Steels

  • Laitinen, R.;Porter, D.;Dahmen, M.;Kaierle, S.;Poprawe, R.
    • International Journal of Korean Welding Society
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    • v.2 no.2
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    • pp.7-13
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    • 2002
  • A comparison of the welding performance of ship hull structural steels has been made. The weldability of steels especially designed for laser processing was compared to that of conventional hull and structural steels with plate thicknesses up to 12 mm. Autogenous laser beam welding was used to weld butt joints as well as skid and stake welded T-joints. The welds were assessed in accordance with the document "The Classification Societies" Requirements for Approval of $CO_2$ Laser Welding Procedures" Small imperfections in the weld only grew slightly in root bend tests and they only had a minor influence on the fatigue properties of laser fillet welded joints. In Charpy impact tests, the 27 J transition temperature of the weld metal and HAZ ranged from below -60 to $-50^{\circ}C$. The amount of martensite in the weld metal depended on the carbon equivalent of the steel with the highest amounts and highest hardness levels in conventional EH 36 (389 HV 5). Thermomechanically rolled steels contained less martensite and showed a correspondingly lower maximum hardness.ximum hardness.

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COMPARATIVE STUDY ON THE WELDABILITY OF DIFFERENT SHIPBUILDING STEELS

  • Laitinen, R.;Porter, D.;Dahmen, M.;Kaierle, S.;Poprawe, R.
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.222-228
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    • 2002
  • A comparison of the welding performance of ship hull structural steels has been made. The weldability of steels especially designed for laser processing was compared to that of conventional hull and structural steels with plate thicknesses up to 12 mm. Autogenous laser beam welding was used to weld butt joints as well as skid and stake welded T-joints. The welds were assessed in accordance with the document "The Classification Societies′ Requirements for Approval of $CO_2$ Laser Welding Procedures". Small imperfections in the weld only grew slightly in root bend tests and they only had a minor influence on the fatigue properties of laser fillet welded joints. In Charpy impact tests, the 27 J transition temperature of the weld metal and HAZ ranged from below -60 to -5$0^{\circ}C$. The amount of martensite in the weld metal depended on the carbon equivalent of the steel with the highest amounts and highest hardness levels in conventional EH 36 (389 HV 5). Thermomechanically rolled steels contained less martensite and showed a correspondingly lower maximum hardness.

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Effect of notch location on the toughness of narrow gap weldment (노치위치에 따른 Narrow Gap 용접부의 인성변화)

  • 김희진;신민태;원정규
    • Journal of Welding and Joining
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    • v.4 no.1
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    • pp.40-46
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    • 1986
  • This investigation studied the toughness variations in the narrow gap weldment with the notch location. Specimens with the notch at the center of the weld metal showed the lowest toughness. As the location of notchmoves to fusion line, the impact properties improve reaching a maximum at the fusion boundaries. This improvement in toughness can be explained by the microstructural feature showing in the narrow gap weldment. "one pass/layer" technique performed in narrow gap welding results in the increased proportion of refined structure as approaching to fusion boundary from weld center and thus leave 100% refined structure along the fusion boundary. HAZ also shows 100% refined structure with respect to base metal structure accompanied with the significant suppression of ductile-brittle transition temperature.mperature.

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Control of Grain Size on Friction Stir Welded AZ31 and AZ91 (AZ31과 AZ91의 마찰교반용접부 결정립 크기 제어)

  • Gwon, Gi-Su;Lee, Chang-U;Kim, Mok-Sun;Sato, Yutaka S.;Kim, Jeong-Han
    • Proceedings of the KWS Conference
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    • 2007.11a
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    • pp.328-331
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    • 2007
  • It was carried out to evaluate microstructure and mechanical properties of friction stir welded(FSW) on magnesium alloys. Two types magnesium alloy was used in this work, AZ31 wrought and AZ91 cast magnesium alloy. Microstructure near the weld zone showed general weld structures such as stir zone(SZ), thermo-mechanically affected zone(TMAZ) and heat affected zone(HAZ). In the AZ91 alloy, the SZ had a fine grain size and $\beta$ phase particles which were well distributed in matrix. It was characterized to redistribute by partial or full re-solution of the $\beta$ phase which is coarse in base metal during FSW processing. The hardness of the SZ slightly increase than the base metal in AZ31 Mg alloy.

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Analysis of the Residual Stresses and Fatigue Strenth in Aluminum Alloy Weldments (AI 합금 용접부의 잔류응력 및 피로강도 해석)

  • 차용훈
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 1996.03a
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    • pp.177-182
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    • 1996
  • The objective of this thesis is to investigate the influence of welding residual stresses on the fatigue growth behavior of welding residual stresses on the fatigue growth behavior of cracks located transverse to the weld bead. For this purpose, G.T.A. (Gas Tungsten Arc) welding was performed on the Al. Alloy 1100-0 plate and the same initial crack is made on HAZ(Heat Affected Zone), weld metal and base metal respectively. C.T.(Compact Tension) specimens were used as experimental material. Initial welding residual stresses were measured by using strain gage sectioning method. All specimens were tested under constant amplitude load with stress ratio R=0.1

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Mechanism of Crack Formation in Pulse Nd:YAG Laser Spot Welding of Al Alloys (Al합금 펄스 Nd:YAG 레이저 점 용접부의 균열 발생기구)

  • 하용수;조창현;강정윤;김종도;박화순
    • Journal of Welding and Joining
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    • v.18 no.2
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    • pp.86-94
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    • 2000
  • This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7N01 spot-welded by pulse Nd : YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed : center line crack({TEX}$C_{C}${/TEX}), diagonal crack({TEX}$C_{D}${/TEX}), and U shape crack({TEX}$C_{U}${/TEX}). Also, HAZ crack({TEX}$C_{H}${/TEX}) was observed in the HAZ region, furthermore, mixing crack({TEX}$C_{M}${/TEX}) consisting of diagonal crack and HAZ crack was observed. White film was formed at th hot crack region in the fractured surface after it was immersed to 10% NaOH water. In the case of A5083 alloy, white films in {TEX}$C_{C}${/TEX} crack and {TEX}$C_{D}${/TEX} crack region were composed of low melting phases, {TEX}$Fe_{2}SiAl_{8}${/TEX} and eutectic phases, $Mg_2$Al$_3$ and $Mg_2$Si. Such films observed $CuAl_2$, {TEX}$Mg_{32}(Al,Zn)_{3}${/TEX}, MgZn$_2$, $Al_2$CuMg and $Mg_2$Si were observed in the whitely etched films near {TEX}$C_{C}${/TEX} crack and {TEX}$C_{D}${/TEX} crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Sim in the case of A7N01 alloy, respectively. The {TEX}$C_{C}${/TEX} and {TEX}$C_{D}${/TEX} cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of {TEX}$C_{M}${/TEX} crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The {TEX}$C_{U}${/TEX} crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification.

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THE EVALUATION OF MICROSTRUCTURE AND MECHANICAL PROPERTIES OF FRICTION STIR WELDEDAL-MG-SI ALLOY

  • Lee, Won-Bae;Yeon, Yun-Mo;Jung, Seung-Boo
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.499-504
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    • 2002
  • The microstructural change associated with the hardness profile in friction stir welded, age-hardenable 6005 Al alloy had been evaluated. Frictional heat and plastic flow during friction stir welding created the fine recrystallized grain (Stir Zone, SZ), the elongated and recovered grain (Thermo-Mechanical Affected Zone, TMAZ) in the weld zone. Heat affected zone (HAZ), which could be only identified by hardness test because there is no difference in the grain structure compared with that of the base metal, was formed beside the weld zone. A softened region had been formed near the weld zone during friction stir welding process. The softened region was characterized by the dissolution and coarsening of the strengthening precipitate during the friction stir welding. The sound joints of 6005 Al alloys were successfully formed under a wide range of the friction stir welding conditions.

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