Papers by Keyword: Dissimilar Weld Joint

Abstract: By the non-destructive testing of a dissimilar weld joint (DWJ) of cold collector DN 1100 (CC) on a steam generator, indications were found on inner-side cold collector’s surface at the root position of the examined weld. All the identified indications were very similar in shape and form, therefore, it was decided to cut out a part of the damaged site from this type of DWJ DN 1100 and get the obtained ring (real piece of material) for complex metallographic analysis. This paper briefly describes the results and recommendations found for the future reference during the next long‑term operation induced ageing and degradation of critical steam generator parts in NPP Bohunice Unit 4. There are summarized the results obtained from evaluation of original DWJ material.

Abstract: The research shows the possibility of increasing the structural strength of the weld joints of EP517 steel and 36NKhTYu iron-nickel alloy as applied to the combined bandage of the high-speed rotor of an electric machine, due to the effect of local strengthening of the soft interlayer. The technology of electron-beam welding of 36NKhTYu alloy to EP517 steel with free root formation, which allows to obtain narrow welds, is described. The results of metallographic researches and mechanical tests of weld joints with different weld widths are presented, which showed that the structure and properties of the weld metal on samples with different weld widths are almost identical. The tension test results of weld joints demonstrate a significantly greater ultimate tensile stress, compared to the ultimate tensile stress of the weld metal. Also, it was established that, due to the local strengthening phenomena the smaller the weld width, the stronger the welded joint is. In addition, the use of heat treatment after welding allows us to increase the strength properties of the weld metal and the heat-affected zone of the 36NKhTYu alloy, due to the formation of the hardening γ’-phase. The possibility of increasing the ultimate tensile strength of the weld up to 98% of the ultimate tensile stress value of EP517 steel (as the less durable of both welded materials), due to heat treatment and reducing the weld width, is demonstrated.

Abstract: The crack growth behavior in dissimilar weld joints is affected by the mechanical heterogeneity of materials. The subcritical crack growth in dissimilar weld joints was simulated by adopting extended finite element method. The results indicated that the strength mismatch will affected the subcritical crack growth behavior. The growth direction of subcritical crack in material with higher strength will deviate to the interface, and the crack may advance through the interface to material with lower strength if the strength mismatch is critical. The cracks will advance away from the interface if the subcritical crack in soft material.

Abstract: Microstructure and material mechanical property in the fusion boundary (FB) region of dissimilar weld joints in light water reactors are quite complicated and different from the bulk material, which make it more susceptible to stress corrosion cracking (SCC) and produce high weld residual stress. To investigate SCC behavior in the FB region of an Alloy 182-A533B dissimilar weld joint, considering the mechanical heterogeneity, mechanical parameters ahead of crack tip with different sampling location are analyzed. It suggests that the stress near crack tip would be significantly higher in a high yield stress material while the strain would be much smaller, and the effect of the material properties around FB region on strain is smaller than that on stress. The result of J-integral indicates FB region would be a barrier when crack in Alloy 182 weld propagates towards LAS.

Abstract: In this study, microstructure and mechanical properties of dissimilar weld joints between 2.25Cr-1Mo ferritic steel and 316L austenitic stainless steel, with and without an Inconel-182 buttering layer, have been investigated. The buttering layer widths produced on the machined edges of the ferritic steel plate were 3 and 5 mm. The dissimilar weld joints were butt-welded using a SMAW process with Inconel-182 electrodes. The results indicate that the ferritic base metal dilution effects are minimized due to buttering and a more uniform distribution of Fe, Ni, Cr and Nb contents is established over a broad region within the fusion zone. Moreover, a microstructure consisting of combined columnar and equiaxed dendrite with interdendritic Nb-rich particles is developed within the fusion zone as a result of buttering. Mechanical tests show that the average hardness, tensile ductility and impact energy of the weld metal were enhanced with increasing width of the buttering, while tensile strength properties were unaffected. It is observed that fracture surfaces of tensile specimens exhibit ductile features composed of ductile tear ridges with numerous interspersed dimples. However, the dominant fracture mode is noted to change from interdendritic to transdendritic with the use of a buttering layer.

Abstract: In this paper is revealed the structural transformations and diffusion processes that take place as a result of the local thermo-mechanical treatment regimes specific to friction welding of nitrided and not nitrided quenched and tempered steels. To obtain welded joints with good mechanical properties it is necessary to remove the nitrided layer from the contact surfaces.

Abstract: This paper describes the evaluation of the creep behavior with two types of matching filler metals for 2.25Cr-1.6W(T23)/Mod. 9Cr-1Mo(T91) dissimilar weld joint. Through the welding procedure qualification tests prior to the creep tests, optimum PWHT holding times at 745±5oC were determined as 30minutes for T23 matching filler metal and 60minutes for T91 matching filler metal. It was also confirmed that carbon migration across the weld interfaces and the softened area at HAZ occurred during PWHT. Creep rupture tests were carried out at 575-650oC and 70-220MPa for two dissimilar metal welds manufactured by an optimum PWHT condition. From the comparison of creep rupture strength, it was shown that the creep strength of the welded joint including T23 matching filler metal was similar to that of T23 base material and somewhat higher than that of the welded joint including T91 matching filler metal. From metallurgical study on the crept specimen, the creep damage of T23/T91 dissimilar weld joints could occur at T23 side IC HAZ and near the T23/T91 weld interface simultaneously. However, the final failure locations seemed to depend on the filler metal and the cause of this phenomenon might be regarded as the additional effect of carbon migration across the weld interfaces. It is thought that the dissimilar weld including T91 filler metal which failures at T23 side CG HAZ subject to both metallurgical notch and carbon migration become more susceptible to creep damage than that including T23 filler metal in which the carbon depletion occurs at the T23 filler metal with higher creep strength than T23 HAZ. T23 filler metal can therefore be proposed for matching filler metal of T23/T91 dissimilar weld joints