• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1982-1989
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• 1991

The effect of heat treatments were considered on the residual stress fields of AISI 4130 weldments. In experiments, various heat treatments such as preheating, postheating, stress relieve annealing and hardening treatment were carried out for the GTA weldments and the residual stress was measured by using the hole drilling method. The post weld heat treatment at 230.deg.C, which aimed mainly to prevent the possible weld cracking, was found to have only a negligible effect on the welding residual stress distribution, while the annealing treatment at 600.deg.C almost completely removes the residual stress. It was also revealed that the hardening treatment causes no further residual stresses in weldments.

• Journal of Korean Society of Steel Construction
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• v.29 no.1
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• pp.37-48
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• 2017

In this research, 9 SAW welding specimens with 1 hour post-heat treatment (PH1) and 2 hours (PH2) were experimented to confirm the weldability and the joint performance of 60mm thickness HSA800 steel. SAW tests with PH1 & PH2, including weld impact test, bend test, hardness test, macroscopic test, and microscopic test, had a good test results. However, from the chemical composition test results, P composition was not satisfied with Korean Industrial Standards(KS). According to the weld-zone tensile tests, 2 hours post-heat SAW is recommended because the mechanical characteristics of SAW PH2 were better than those of SAW PH1.

• Journal of Welding and Joining
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• v.1 no.2
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• pp.45-52
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• 1983

Many pressure vessels for the hot H$\sub$2//H$\sub$2/S service are made of 2+1/4Cr-1Mo steel with austenitic stainless steel overlay to combat agressive corrosion due to hydrogen sulfide. Hydrogen dissolves in to materials during operation, and sometimes gives rise to unfore-seeable damages. Appropriate precautions must, therefore, be taken to avoid the hydrogen induced damages in the design, fabrication and operation stage of such reactor vessels. Recently, hydrogeninduced cracking (or Disbonding) was found at the interface between base metal and stainless weld overlay of a desulfurizing reactor. Since the stainless steel overlay weld metal is subjected to thermal and internal-pressure loads in reactor operation, it is desirable for the overlay weld metal to have high strength and ductility from the stand point of structural safety. In section III of ASME Boiler and Pressure Vessel Code, Post-Weld Heat Treatment(PWHT) of more than one hour per inch at over 1100.deg. F(593.deg. C) is required for the weld joints of low alloy pressure vessel steels. This heat treatment to relieve stresses in the welded joint during construction of the pressure vessel is considered to cause sensitization of the overlay weld metal. The present study was carried out to make clear the diffusion of carbon migration by PWHT in dissimilar metal welded joint. The main conclusion reached from this study are as follows: 1) The theoretical analysis for diffusion of carbon in stainless steel overlay weld metal does not agree with Fick's 2nd law but the general law of molecular diffusion phenomenon by thermodynamic chemical potential. 2) In the stainless steel overlay welded joint, the PWHT at 720.deg. C for 10 hours causes a diffusion of carbon atoms from ferritic steel into austenitic steel according to the theoretical analysis for carbon migration and its experiment. 3) In case of PWHT at 720.deg. C for 10 hours, the micro-hardness of stainless steel weld metal in bonded zone increase very highly in the carburized layer with remarkable hardening than that of weld metal.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.314-321
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• 1987

Post weld heat treatment (PWHT) of weldment of the low alloy Cr-Mo steel, in general, is carried out not only to remove residual stress and hydrogen existing in weldment but to improve fracture toughness of weld heat affected zone (HAZ). There occur some problems such as toughness decrement and stress relief cracking (SRC) in the coarse grained region of weld HAZ when PWHT is practiced. Especially, embrittlement of structure directly relates to the mode of fracture and is appeared as the difference of fracture surface such as grain boundary failure. Therefore, in this paper, the effect of heating rate on PWHT embrittlement under the various kinds of stresses simulated residual stress in weld HAZ was evaluated by COD fracture toughness test and observation of fracture surface. Fracture toughness of weld HAZ decreased with increment of heating rate under no stress, but it was improved to increment of heating rate under the stress. Grain boundary failure didn't almost appear at the heating rate of 600.deg.C/hr but it appeared from being the applied stress of 294 MPa at 220.deg.C/hr and 196 MPa at 60.deg.C/hr.

• Plant Journal
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• v.10 no.2
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• pp.48-59
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• 2014

Coupons which have same figure as weld joint of the forged steel valves and 1 inch nominal weld thickness were manufactured using ASTM A182 F92 material. After welding with GTAW method, the welded specimens have been post-weld heat treated at $705^{\circ}C$, $735^{\circ}C$, $750^{\circ}C$, $765^{\circ}C$, $795^{\circ}C$ and $825^{\circ}C$ for 1 hour per 1 inch nominal weld thickness each (Group 1) to evaluate characteristics of welds based on various holding temperature. Indeed, 3 welded specimens were post-weld heat treated for 30 minutes, 1 hour and 2 hour (Group 2) at $735^{\circ}C$ to evaluate characteristics of welds based on various holding time. Hardness values were measured at the weld metal, heat affected zone and base metal to observe hardness change depending on the condition. As a result of the evaluation, appropriate holding temperature for PWHT is proved as $750^{\circ}C$ and $765^{\circ}C$ for 1hour per 1 inch nominal weld thickness. Indeed, holding for 1 hour per 1 inch nominal weld thickness was insufficient for PWHT effect when the holding temperature was at $735^{\circ}C$. The microstructure of post-weld heat treated weld metal was determined as tempered-martensite structure.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.359-364
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• 2004

We investigated the effect of weld details on fatigue behavior of a material, JIS SM 490 A, with yielding strength of about 350 MPa and tensile strength of about 520 MPa. Tensile tests, instrumented indentation tests and fatigue tests were carried out on double V-grooved butt weld plates such as reinforcement removed, as-welded and weld toe ground. In addition plates with transverse fillet welded web, load carrying cruciform fillet welded plates, non-load-carrying cruciform fillet welded plates and longitudinal butt welded plates were tested. S-N curves for the above specimens were obtained and analyzed

• Plant Journal
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• v.6 no.3
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• pp.53-61
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• 2010

This paper presents failure analysis on weld-joint of the waterwall tubes in USC boilers. Visual inspections were performed to find out the characteristics of the fracture. Additionally both microscopic characteristics and hardness test were carried out on failed tube samples. Failures seem to happen mainly because the welding process such as preheating and PWHT(post-weld heat treatment) was not conducted strictly. Thus, this paper has the purpose to describe the main cause of the poor welding process and to explain how to prevent similar failures in those weld-joints.

• Nuclear Engineering and Technology
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• v.46 no.3
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• pp.413-422
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• 2014

Presented in this study are the variations of microstructures and mechanical properties with tempering and Post-Weld Heat Treatment (PWHT) conditions for SA508 Gr.4N steel used as Reactor Pressure Vessel (RPV) material. The blocks of model alloy were austenitized at the conventional temperature of $880^{\circ}C$ then tempered and post-weld heat treated at four different conditions. The hardness and yield strength decrease with increased tempering and PWHT temperatures, but impact toughness is significantly improved, especially in the specimens tempered at $630^{\circ}C$. The sample tempered at $630^{\circ}C$ with PWHT at $610^{\circ}C$ shows optimum mechanical properties in hardness, strength, and toughness, excluding only the transition property in the low temperature region. The microstructural observation and quantitative analysis of carbide size distribution show that the variations of mechanical properties are caused by the under-tempering and carbide coarsening which occurred during the heat treatment process. The introduction of PWHT results in the deterioration of the ductile-brittle transition property by an increase of coarse carbides controlling cleavage initiation, especially in the tempered state at $630^{\circ}C$.

• Journal of Welding and Joining
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• v.34 no.6
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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.

• Corrosion Science and Technology
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• v.2 no.5
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• pp.219-224
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• 2003

Crevice corrosion of stainless steels in natural seawater was investigated for several post weld treatments; as-annealed, as-welded, pickled, and ground. The results confirmed the effect of the biofilm on the cathodic reaction leading to an ennoblement of the rest potential. The degree of ennoblement of corrosion potential depends on the surface finish. As-annealed and pickled samples show stable corrosion potential approaching to 200 ~ 300 mV (SCE) while as-welded and ground samples show the fluctuating corrosion potential. This points to a situation where there are conflicting effects determining the trend in free corrosion potential. Crevice corrosion initiation will tend to pull the free corrosion potential in the active direction, whereas the presence of biofilm will tend to ennoble corrosion potential. There was no visible attack on UNS S31803, S32550, and 2205W. Therefore, those stainless steel grades appeared to be resistant to crevice corrosion in natural seawater on condition of weld metal.