• Title/Summary/Keyword: PWHT

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Statistical Properties of Vickers Hardness of Post Weld Heat Treated Friction Welded Parts in Alloy718 (Alloy718 마찰용접 후열처리재의 비커스 경도의 통계적 성질)

  • Kong, Yu-Sik;Kwon, Hyeok-Yong;Kim, Seon-Jin
    • Journal of Ocean Engineering and Technology
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    • v.23 no.6
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    • pp.105-110
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    • 2009
  • The objective of this paper is to investigate the statistical properties of Vickers hardness (HV) for friction welded parts in a Ni-based super alloy (Alloy718). In the case of post weld heat treatment (PWHT) parts, hardness tests were repeated for three different applied loads, 100, 200, and 300 g, with a duration time of 10 seconds. The arithmetic means of the Vickers hardness in heat affected zone (HAZ) materials were smaller than those of the base metal (BM) in all of the applied loads. The coefficient of variation (COV) for the BM and HAZ decreased by increasing the applied load. The probability distribution of the Vickers hardness followed the Weibull distribution well. The distribution of the Vickers hardness was not found to be symmetric. The shape parameter and scale parameter increased by increasing the applied load at both the BM and HAZ.

The effect of Heat input, Shielding Gas(Ar80% + $CO_2$20%), PWHT on the mechanical properties of HSB600 steel Weldments (HSB600강 용접에서 입열량, 보호가스, 용접후 열처리가 미세조직과 기계적 특성에 미치는 영향)

  • Ju, Dong-Hwi;Lim, Young-Min;Kim, Nam-Hoon;Koh, Jin-Hyun
    • Proceedings of the KAIS Fall Conference
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    • 2011.12b
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    • pp.394-397
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    • 2011
  • The effects of heat input(1.4~3.2kJ/mm), shielding gas(Ar80%+$CO_2$20%) and postweld heat treatment(PWHT, $600^{\circ}C$, 40hr.) on the TMCP HSB600 steel weldments made by GMAW process were investigated. The tensile strength and CVN impact energy of as-welded specimens decreased with increasing heat input. The fine-grained acicular ferrite was mainly formed in the low heat input while polygonal and side plate ferrites were dominated in the high inputs. High performance steel for bridges requires higher performance in tensile and yield strength, toughness, weldability, etc. Thus, the purpose of the experiment is to study HSB 600 in GMAW.

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Effect of welding residual stress on operating stress of nuclear turbine low pressure rotor

  • Tan, Long;Zhao, Liangyin;Zhao, Pengcheng;Wang, Lulu;Pan, Jiajing;Zhao, Xiuxiu
    • Nuclear Engineering and Technology
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    • v.52 no.8
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    • pp.1862-1870
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    • 2020
  • The purpose of this study is to investigate the effect of welding residual stress on operating stress in designing a nuclear turbine welded rotor. A two-dimensional axisymmetric finite element model is employed to calculate the residual stress before and after post weld heat treatment (PWHT), and then the superposition of residual stress after PWHT and operating stress at normal speed and overspeed were discussed. The investigated results show that operating stress can be affected significantly by welding residual stress, and the distribution trend of superposition stress at the weld area is mainly determined by welding residual stress. The superposition of residual stress and operating stress is linear superposition, and the hoop stress distribution of superposition stress is similar with the distribution of residual stress. With the increasing overspeed, the distribution pattern of the hoop superimposed stress remains almost unchanged, while the stress level increases.

Evaluation of Influence on the Fatigue Strength of Residual Stresses at the Welded Toe of Welded Structure. (용접구조물 요접토우부의 잔류응력이 피로강도에 미치는 영향 평가)

  • 차용훈;김하식;김일수;성백섭
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.10 no.4
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    • pp.7-13
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    • 2001
  • This Study is to investigate the influence of weld residual stresses on the fatigue crack growth behaviors in pressure ves-sel reinforcement. In order to perform this study, the automatically welded specimens are prepared. The material is ASTM A516 grade 60 steel used in pressure vessel mainly. For pad-on-plate of skip welding continuous welding and PWHT specimen, fatigue crack initiation is generally initiat-ed at weld starting and end toe zone, and ruptured at weld starting toe zone, Fatigue life if pad-on-plate continuous speci-men is increased more than that of pad-on-plate skip fillet welding specimene about 85% under low load, about 20% under high load, and decreased than that of two-pad continuous welding specimen about 85%. In da/dN-$\Delta$ Κ curve under low load, pad-on-plate skip fillet welding specimen showed retardation on the initial crack, and the fatigue crack growth rate at the low region of $\Delta$Κ greater specimene E(3.8{\times}10^{-6}$mm/cycle). And the fatigue life of welding specimen was smaller than that of PWHT specimen.

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Effect of PWHT on Variability of fatigue Crack Propagation Resitance in TIG Welded Al 6013-T4 Aluminum Alloy (TIG 용접된 Al6013-T4 알루미늄 합금에서 피로균열전파저항의 변동성에서의 PWHT의 영향)

  • Haryadi, Gunawan Dwi;Lee, Sang-Yeul;Kim, Seon-Jin
    • Journal of Power System Engineering
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    • v.15 no.6
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    • pp.73-80
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    • 2011
  • The experimental investigation focuses on an influence of artificial aging time in longitudinal butt welded Al 6013-T4 aluminum alloy on the fatigue crack growth resistance. The preferred welding processes for this alloy are frequently tungsten inert gas welding (TIG) process due to its comparatively easier applicability and better weldability than other gas metal arc welding. Fatigue crack growth tests were carried out on compact tension specimens (CT) in longitudinal butt TIG welded after T82 heat treatment was varied in three artificial aging times of 6 hours, 18 hours and 24 hours. Of the three artificial aging times, 24 hours of artificial aging time are offering better resistance against the growing fatigue cracks. The superior fatigue crack growth resistance preferred spatial variation of materials within each specimen in the Paris equation based on reliability theory and fatigue crack growth rate by crack length are found to be the reasons for superior fatigue resistance of 24 hours of artificial aging time was compared to other joints. The highest of crack propagation resistance occurs in artificial aging times of 24 hours due to the increase in grain size (fine grained microstructures).

Fatigue Life Analysis of Butt-welded Joint with and without Postweld Heat Treatment by Local Strain Approach (국부변형률 방법을 이용한 용접후열처리 전후 시편의 피로수명 해석)

  • Lee, Dong-Hyoung;Seo, Jeong-Won;Goo, Byeong-Choon;Seok, Chang-Sung
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.1086-1091
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    • 2003
  • The problem of residual stresses and fatigue behavior in welded structures is the main concern of welding research fields. The residual stresses and distortions of structures by welding exert negative effect on the safety of mechanical structures. Postweld heat treatment is usually carried out to relieve this residual stresses of welded joints. In this paper the influence of postweld heat treatment on fatigue life of butt-welded joint was investigated. To predict the effect of PWHT, an analytical model is developed by finite element and local strain approach and the result of fatigue life analysis is compared to experimental results. It is demonstrated that fatigue life estimates closely approximate the experimental results and PWHT provides some increase of fatigue lives in long-life fatigue region and no increase in short-life fatigue region because of the residual stress relaxation under tensile loads.

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Diagnosis of cracking in T23 welds for power plant application (보일러용 고강도 T23강의 용접부 손상 원인 분석)

  • Park, Ki-Duck;Ahn, Jong-Suk;Shin, Dong-Hyeok;Lee, Chang-Hee
    • Proceedings of the KWS Conference
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    • 2009.11a
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    • pp.61-61
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    • 2009
  • This paper has been performed in order to figure out the reason of failure in T23 weldments used for boiler tube at 550 $^{\circ}C$. Defects such as cracks and cavities occurred in CGHAZ (coarse grain heat-affected-zone) and multi pass of weld metal, and these crack propagated along grain boundary. Microstructure evolution such as grain growth and carbide precipitation was investigated by optical microscope (OM), transmission electron microscope(TEM). Moreover, Auger electron spectroscope (AES) was employed in order to examine segregation along the grain boundaries. There is significant difference in grain size and precipitation distribution in the region where cracking took place. In addition, sulfur segregation was observed. Based on the results of this investigation, it has been possible to establish that this type of cracks were consistent with reheat cracking and creep damage. Selection of optimal filler metal, heat input, and PWHT temperature is required for prevention in order to avoid this type of cracking.

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A Study on the Post-Weld Heat Treatment Effect Affecting Corrosion Behavior and Mechanical Property of Welding Part of RE36 Steel for Marine Structure (해양구조물용 RE36강 용접부의 부식거동 및 기계적 특성에 미치는 용접후 열처리 효과에 관한 연구)

  • 김성종;문경만
    • Journal of Welding and Joining
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    • v.19 no.1
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    • pp.65-74
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    • 2001
  • A study on the corrosion behavior in case of As-welded and PWHT temperature 55$0^{\circ}C$ of welding part of RE36 steel for marine structure was investigated with parameters such as micro-Vickers hardness, corrosion potential measurement of weld metal(WM), base metal(BM) and heat affected zone(HAZ), both Al anode generating current and Al anode weight loss quantity under sacrificial anode cathodic protection conditions. And also we carried out slow strain rate test(SSRT) in order to research both limiting cathodic polarization potential for hydrogen embrittlement and optimum cathodic protection potential as well as mechanical properties by post-weld heat treatment(PWHT) effect. Hardness of HAZ was the highest among three parts(WM, BM and HAZ) and the highest galvanic corrosion susceptibility was HAZ. And the optimum cathodic polarization potential showing the best mechanical properties by SSRT method was from -770mV to -875mV(SCE). In analysis of SEM fractography, applied cathodic potential from -770mV to -875mV(SCE) it appeared dimple pattern with ductile fracture while it showed transgranular pattern (Q. C : quasicleavage) under -900mV(SCE). However it is suggested that limiting cathodic polarization potential indicating hydrogen embrittlement was under -900mV(SCE).

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A Study on the Fatigue Crack Growth Behaviour for the Welded Configuration in Pressure Vessel Stiffener (압력용기 보강재의 용접 형태에 따른 피로균열성장 거동에 관한 연구)

  • 차용훈;김하식;성백섭
    • Journal of the Korean Society of Safety
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    • v.16 no.3
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    • pp.1-6
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    • 2001
  • The study is to investigate the influence on the fatigue crack growth behaviors for the welded configuration in pressure vessel stiffener. In order to perform this goal, the automatic welded specimens were prepared. The material is ASTM A516 grade 60 steel used in pressure vessel mainly. In skip welding of pad-on-plate, continuous fillet welding and PWHT specimen, fatigue crack is generally initiated at the starting and end old toe zone, and ruptured at the starting old toe zone. The fatigue life of pad-on-plate of the continuous fillet welding specimen is larger than that of pad-on-plate skip fillet welding specimen about 85% under low load, about 20% under high load and less than that of two-pad continuous fillet welding specimen about 85%. In da/dN-$\Delta$K curve under low load, skip fillet welding specimen of pad-on-plate showed retardation on the initial crack, and the fatigue crack growth rate at the low region of $\Delta$K greater specimen E($3.8 {\times} 10^{-6}mm/cycle$). And the fatigue life of welding specimen was smaller than that of PWHT specimen.

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Effect of Post Weld Heat Treatment for Crystal Orientation Distribution on Friction Stir Welds of Al-Mg-Si Series Aluminum Alloy Sheets (Al-Mg-Si계 알루미늄 합금 판재 마찰교반접합부의 결정 방위 분포에 대한 용접후열처리의 영향)

  • Lee, Kwang-Jin
    • Journal of Welding and Joining
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    • v.27 no.6
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    • pp.62-67
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    • 2009
  • Friction stir welding (FSW) was carried out for Al-Mg-Si series aluminum alloys which are being used for automotive body structure. Consequently, Post weld heat treatment (PWHT) was applied to the friction stir welds to evaluate the effect of the paint baking process which is one of the automotive fabrication process on friction stir welded zone (FSWZ) in 443K for 1.2Ks. Grain structure and its crystal orientation distribution was measured about both the as welded specimens and the post weld heat treated specimens. An optical microscope (OM) and an field emission scanning electron microscope (FE-SEM) was used for observing the grain structure and measuring its crystal orientation distribution, respectively. Changes on the grain structure and its crystal orientation distribution were not detected. From the present results, it was confirmed that the paint baking process after FSW do not affect on the grain structure and its crystal orientation distribution of FSWZ. The comprehensive investigations will be performed for various automotive aluminum alloys manufactured by different processes, in the future.