• Journal of Welding and Joining
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• v.8 no.3
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• pp.39-52
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• 1990

The research is to insure the soundness of the stainless steel overlaid weld metal(21/4Cr-IMo steel + SUS 309L) for a pressure vessel application. Detail studies were conducted for the PWHT influence on the micrstructure and intergranular corrosion characteristics of the overlaid weld metal as well as initiation of hydrogen embrittlement crack(or Disbonding) when welded metal are exposed to the hydrogen atmosphere. Hydrogen was experimentally charged to the overlaid weld metal in order to study PWHT effect on the susceptibility of hydrogen embrittlement crack. The results of this research are as follows: 1. At the bond region, austenite grain of the stainless steel side became coarsed and Cr23C6 type carbide was precipitated at the coarsed austenitic grain boundaries. Intergranular Corrosion width(by Straiss test) increased with increasing PWHT temperature and PWHT time.

• 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 the Korean Society of Industry Convergence
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• v.24 no.5
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• pp.517-523
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• 2021

In this study, in the selection of materials for the elements of a small plant, those with high resistance to corrosion are selected and the material properties of coatings for corrosion prevention are evaluated. In addition, corrosion characteristics and material analysis were performed on the welded part, and the hardness characteristics of the welded part, heat-affected part, and the base metal were evaluated. In the case of the post-weld-heat-treated(PWHT) specimen, the corrosion resistance of STS 316 was lower than that of the specimen without the PWHT due to the formation of intergranular carbide. As a result of evaluating the distribution of the hardness of the weld before and after the PWHT, the hardness of the specimen after the PWHT increased by about 20 Hv. As a result of the corrosion test on the welded specimen, the weight loss tended to increase as the time increased. In the case of the PWHT specimen, the corrosion resistance tended to be significantly lower than that of the specimen without PWHT due to the formation of intergranular carbide.

• Journal of Welding and Joining
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• v.6 no.2
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• pp.30-39
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• 1988

Generally, as the welded region of weld structures has the incomplete bead and welded deposit which are able to behave like the surface cracks occasinally, there is a high possibility that the fatigue fracture of the weld structures is due to the surface cracks on the wlded region. This study was done to investigate the effects of post weld heat treatment (PWHT) on the fatigue behaviors of the surface crack of the heat affected zone (HAZ) for the multi-pass welds under the repetitive pure bending moment. The obtained results are summarized as follows : 1. The crack grows to the depth direction initially as the number of cylces increase, the amount of crack length is increased for the surface dir3ction and cive versa for the depth direction. 2. The fatigue life is increased in a order of as weld, PWHT specimens and parent. 3. As the number of cycles increase, the crack length is increased to th surface direction. The increase of the depth length is blunted at the center of specimen thickness. 4. The fatigue crack growth of PWHT specimens to the surface direction is dependent upon the holding time and applied stress during PWHT. In order words, the crack growth rate decreases with the holding time and increases with the applied stress during PWHT. 5. As the crack grows, the aspect formed in the course of crack propagation approaches to semicircle for parent and ellipse with the largest semidiameter for PWHT ($1/4hr, 15kgf/mm^2$) 6. At depth direction, it is difficult to apply to the paris' equation because of the scattered data between the crack growth rate and the stress intensity factor range.

• Journal of Welding and Joining
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• v.21 no.6
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• pp.12-15
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• 2003

• Journal of Welding and Joining
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• v.22 no.5
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• pp.26-31
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• 2004

In order to propose the optimum welding condition for field application, the effects of welding heat input and cooling rate at PWHT on the mechanical properties were investigated. Submerged arc welding of 1.25Cr-0.5Mo steel for pressure vessel was conducted at welding heat inputs of 15.2kJ/cm, 30.9kJ/cm, and 44.8kJ/cm, and cooling rates of 184$^{\circ}C$/hr, 55$^{\circ}C$/hr, and 2$0^{\circ}C$/hr at PWHT. From the test results, as the welding heat input increase up to 30.9kJ/cm, the changes of microstructure and impact toughness were small. At the heat input of 44.8kJ/cm, however, toughness decreased obviously due to the coarsening of coarse-grained HAZ and formation of ferrite at bainite grainboundary of weld metal. On the other hand, cooling rates at PWHT did not effect on the changes in microstructure and mechanical properties. Even though tensile strength and impact toughness at all welding conditions of this study were above the minimum specification requirement, it was confirmed that heat input of 30.9kJ/cm was the optimum welding condition to improve welding performance by higher heat input.

• Journal of Welding and Joining
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• v.2 no.2
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• pp.54-61
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• 1984

Construction of welding structure is greatly dependent upon welding heat cycle. Fracture toughness is decreased remarkablely due to coarse grained HAZ and inequal residual stress of three dimensions to originate in welding. Post weld heat treatment(PWHT) is carried out to increase the fracture toughness of HAZ and to remove the residual stress. There occur some problem such as toughness decrement and stress relief cracking(SRC) in the coarse grained HAZ subject to the effect of tempering treatment. Therefore, in this paper, the effect of heat inputs affecting cooling rate and PWHT under the no stress on fracture toughness were evaluated by crack opening displacement (COD), SEM and micro-hardness test. Experimental results are as follows; 1. Fracture toughness of weld HAZ is dependent upon weld heat cycle and it is decreased with increment of heat input, but the degree of improvement of fracture toughness after PWHT was linearly increased with heat input. 2. Hardness of the parent metal is not changed, but the softening of coarse grained HAZ is remarkable due to PWHT. 3. Fracture surface of as-weld show the perfect brittle fracture with the cleavage fracture, but after PWHT they appear the ductile fracture surface with dimple.

• Proceedings of the KWS Conference
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• 2006.10a
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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.

• Journal of Welding and Joining
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• v.15 no.2
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• pp.64-71
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• 1997

In order to define the effects on shapes of welding joint, during Post Welding Heat Treatment (PWHT), we have carried out numerical analysis on the several test pieces by using computer program which was based on thermal-elasto-plastic-creep theories for the study. And then, welding residual stresses after PWHT were measured same test-pieces to compare with the results of numerical analysis. The main results obtained from this study is as follows: 1) The distribution modes of welding residual stresses are same on the all test pieces after and during PWHT by the both sides (measurement and numerical analysis). 2) The mechanical difference for change the thickness of plate and bevel angle are not appeared. 3) In a mechanical point of view (like material quality test, welding deformation etc.), manimum bevel angle (40$^{\circ}$.) is more suitable than maximum bevel angle (70$^{\circ}$).

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.45-47
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• 2007

주강소재 보수용접부의 품질 및 용접생산성 향상을 위해 기존 용접후열처리 조건(이하 PWHT)을 모재에 적용하는 품질열처리(이하 NTT)로의 대체 및 반자동 FCAW 용접방법의 적용 가능성을 확인하기 위해 상온 및 고온 물성평가(고온인장강도, 크리프 파단강도)를 수행한 결과, 제작 공정 측면에서 FCAW의 적용이 가능한 것으로 확인되었다. 또한 PWHT 대신 NTT를 적용함으로서 용접방법별 물성 편차가 줄어드는 NTT 열처리의 긍정적 효과가 확인되어, 궁극적으로 기존 PWHT 및 NTT 모두 적용이 가능한 것으로 확인되었다.