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Vol.63, No.6, 399 ~ 410, 2025
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| Title |
| Effect of Post-Weld Heat Treatment on the Microstructure and Mechanical Properties of Electron Beam Welded Mn-Mo-Ni Low Alloy Steel for Reactor Pressure Vessels |
| 이승욱 Seung Uk Lee , 현세미 Se-mi Hyun , 김민철 Min-chul Kim , 홍석민 Seokmin Hong , 김종민 Jong Min Kim , 이수열 Soo Yeol Lee |
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| Abstract |
| This study investigates the effect of electron beam welding (EBW) on SA508 Gr.3 Cl.1 Mn-Mo-Ni low alloy steel, focusing on changes in the microstructural and mechanical properties of the weld and heat-affected zone (HAZ) under various post-weld heat treatment (PWHT) conditions. The rapid cooling inherent in the EBW process led to the formation of coarse columnar structures consisting of Widmanstätten ferrite and bainite in the weld. In the HAZ, finer low-temperature transformation microstructures, such as martensite and lower bainite, were observed, compared to the weld metal. The formation of these microstructures resulted in increased hardness and residual stresses. To address these effects, PWHT was conducted at 610℃ and 630℃. After PWHT, precipitates formed along the laths within the grains, and the softening of the matrix combined with the relaxation of residual stresses led to decreased hardness and strength, accompanied by improved impact toughness. However, as the PWHT temperature increased, the coarsening of precipitates contributed to an increase in the impact transition temperature. Moreover, despite the application of post-weld quality heat treatment, the segregation of solute atoms at the columnar grain boundaries in the weld metal was not completely eliminated. Consequently, the impact transition properties of the weld metal did not fully recover to the level of the base metal.
(Received 21 March, 2025; Accepted 13 May, 2025) |
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| Key Words |
| SA508 Gr.3, Electron Beam Welding, Post-Weld Heat Treatment, Post-Weld Quality Heat Treatment, Microstructure, Mechanical Properties |
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