• Journal of Welding and Joining
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• 제34권6호
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• pp.47-54
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• 2016

Post-Weld Heat Treatment (PWHT) cracking susceptibility in the weld heat-affected zone (HAZ) of reduced activation ferritic-martensitic (RAFM) steels was evaluated through stress-rupture tests. 9Cr-1W based alloys including different C, Ta and Ti content were prepared. The coarse grained heat-affected zone (CGHAZ) samples were simulated with welding condition of 30 kJ/cm heat input. CGHAZ samples consisted of martensite matrix. Stress rupture experiments were carried out using a Gleeble simulator at temperatures of $650-750^{\circ}C$ and at stress levels of 125-550 MPa, corresponding to PWHT condition. The results revealed that PWHT cracking resistance was improved by Ti addition, i.e., Ti contributed to the formation of fine and stable MX precipitates and suppression of coarse M23C6 carbides, resulting in improvement of stress rupture ductility. Meanwhile, rupture strength increased with increasing solute C content.

• Journal of Welding and Joining
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• 제14권1호
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• pp.75-81
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• 1996

The heat transfer and thermal stress-distribution were numerically determined by using the finite element method for a butt-welded pipe. A mechanical stress relieving(MSR) treatment which has been frequently used in the fabrication of pressure vessels instead of the post weld heat treatment (PWHT) was also simulated to investigate its effect of reducing the residual stress in the welded zone by a mechanical loading.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.273-275
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• 2002

The effect of post-weld heat treatment (PWHT) of marine structures steel was investigated at electrochemical viewpoint. In addition, slow strain rate test (SSRT) was carried out to investigate both electrochemical and mechanical properties by PWHT effect during impressed current cathodic protection. The optimum cathodic protection potential by SSRT was -770 mV(SCE). At the applied cathodic protection potential of -770 mV -850 mV(SCE), the fracture morphology was dimple pattern with ductile fracture, while it was transgranular pattern (Q.C: quasi cleavage) under -875 mV(SCE).

• Journal of Welding and Joining
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• 제27권6호
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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.

• Journal of Welding and Joining
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• 제32권2호
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• pp.29-36
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• 2014

Recently, in order to enhance the function and usefulness of products, cladding of dissimilar materials that maximizes the performance of the material is being widely used in all areas of industry as an important process. Clad steel plate, produced by cladding stainless steel plate, an anticorrosive material, on carbon steel plate, is being used to produce pressure vessels. Stainless steel plate has good corrosion resistance, and carbon steel plate has good rigidity and strength; clad steel can satisfy all of these qualities at once. This study aims to find the ${\delta}$-ferrite behavior, mechanical properties, structure change, integrity and reliability of clad steel weld on hot rolled steel plates. For this purpose, multi-layer welding, repair welding and post weld heat treatment were implemented according to welding procedure specifications (WPS). In order to observe the mechanical properties and toughness of clad steel weld zone, post weld heat treatment was carried out according to ASME Sec. VIII Div.1 UW-40 procedure for post weld heat treatment. With heat treatment at $625^{\circ}C$, the hold time was used as the process variable, increased by intervals that were doubled each time, from 80 to 1,280 min. The structure of weld part was typical cast structure; localized primary austenite areas appeared near central vermicular ferrite and fusion line. The heat affected zone showed rough austenite structure created by the weld heat input. Due to annealing effects of heat treatment, the mechanical properties (tensile strength, hardness, impact value) of the heat affected area tended to decrease. From the results of this study, it is possible to conclude the integrity of clad steel welds is not affected much in field welding, repair welding, multi-layer welding, post weld heat treatment, etc.

• 대한금속재료학회지
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• 제47권3호
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• pp.139-146
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• 2009

The heat-affected zone (HAZ) of SA508 Gr.4N Ni-Mo-Cr low alloy steel, which has higher Ni and Cr contents than SA508 Gr.3 Mn-Mo-Ni low alloy steel, was investigated on the microstructure and mechanical properties. The HAZ was categorized into seven characteristic zones (CGCG, FGCG, ICCG, SCCG, FGFG, ICIC and SCSC-HAZ) according to the peak temperature from the thermal cycle experienced during multi-pass welding. Post Weld Heat Treatment (PWHT) was conducted in the temperature range of $550{\sim}610^{\circ}C$ for 30 hours to evaluate the effect of PWHT conditions on the microstructure and mechanical properties. Before PWHT, CGHAZ and FGFGHAZ showed high yield strength (YS) ranging from 1000 to 1250 MPa, while YS of SCSCHAZ decreased from 607 MPa (observed for base metal) to 501 MPa. The Charpy impact energies of sub-HAZs fell below 100J at $-29^{\circ}C$, except in the SCSCHAZ. By applying PWHT to sub-HAZ specimens, YS decreased as the PWHT temperature increased. In the case of CGHAZs and FGFGHAZ heat-treated at $610^{\circ}C$, YS dropped drastically to the range of 654~686 MPa. From the Charpy impact test, the upper-shelf energy (USE) increased to approximately 250J and Index temperature ($T_{68J}$) decreased below $-50^{\circ}C$. Specifically, in FGFG, ICIC and SCSC-HAZ, $T_{68J}$ was below -110, which was lower than the case of base metal.

• Journal of Welding and Joining
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• 제5권3호
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• pp.53-61
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• 1987

Post weld heat treatment(PWHT) is usually carried out to remove the residual stress and to improve the microstructure and mechanical properties of welded joints. By the way, welding structure transformed owing to PWHT and reheating for repair loads the random cycles fatigue as offshore welding structure of constant low cycle fatigue as pressure vessel, and then, pre-existing flaws or cracks exist in a structural component and those cracks grow under cyclic loading. Therefore, the effects of PWHT and stress ratio on fatigue crack growth behaviors were studied on the three regions such as HAZ, sub-critical HAZ and deposit metal of welded joints in SM53 steel. Fatigue crack growth behavior of as-weld depended on microstructure and fatigue crack growth rate of HAZ was the lowest at eac region, but after PWHT it was somewhat higher than that of as-wel. In case of applying the stress($10kg/mm^2$) during PWHT, fatigue crack growth resistance tended to increase in the overall range of .DELTA.K.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.96-101
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• 2004

Conventionally, SMAW process was applied to join pipes of RCL, which caused lot of loss in time and cost due to excessive heat input and defects in joining section. Recently, narrow-gap welding(NGW) process was introduced to overcome the disadvantages of SMAW. However, the application of NGW to nuclear power plant is not yet common because safety of NGW process is not proven. In present paper, the welded coupons are made of carbon steel. They are manufactured under different processes; general welding(GW), post-weld heat treatment(PWHT) after GW, repair welding after GW and PWHT with repair welding after GW in carbon steel. Performed are various mechanical tests investigation of microstructure, hardness test, tensile test at room and high temperature, bending test, impact test and J-R test. It is verified that the mechanical properties of carbon steel are greatly changed after repair welding process due to applied heat flux, and that the effect of PWHT is beneficial.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2006년 추계학술발표대회 개요집
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• pp.18-19
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• 2006

The purpose of this study is to evaluate the behavior of residual stress at the weldment of pressure vessel by local Post Weld Heat Treatment(PWHT). In order to do it, residual stress were measured before and after local PWHT by XRD on the test piece first. And then, the results of finite element(FE) analysis based on thermal-elasto-plastic-creep theories were verified by comparing with the measured results.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1995년도 특별강연 및 춘계학술발표 개요집
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• pp.91-93
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• 1995

A study was made to examine the effects of post-weld heat treatment (PWHT) on the toughness and microstructures in the weld heat-affacted zone(HAZ) of Cu-bearing HSLA-100 steel. The Gleeble thermal/mechanical simulator was used to simulate the weld HAZ. The behavior of Cu-precipitates in HAZ is similar to that in base plate. PWHT at 55$0^{\circ}C$ shows highest hardness and lowest toughness, whereas PWHT at $650^{\circ}C$ shows reasonable toughness. Cu precipitated during agcing for increasing the strength of base metal is dissolved during single thermal cycle to 135$0^{\circ}C$ and is precipitated little on cooling and heating during subsequent weld thermal cycle. It precipitates by introducing PWHT.