Effect of Heat Input on Microstructure and Impact Toughness of Thick-walled Component by Submerged Arc Additive Manufacturing
WANG Hu1, WU Shaojie1,2, DONG Yilun1, CHENG Fangjie1,2,*
1 School of Materials Science and Engineering, Tianjin University, Tianjin 300350, China 2 Tianjin Key Laboratory of Advanced Joining Technology, Tianjin 300350, China
Abstract: In this study, the submerged arc additive manufacturing was used to fabricate large thick-walled test parts under different heat inputs, and the influence of heat input on the microstructure and impact toughness was analysed, which provided a theoretical basis for the fabrication of large components in nuclear power, offshore platforms and other fields using the additive manufacturing technology. The results showed that all the deposited metals undergo completely intrinsic heat treatment under low heat input, and the microstructure presented a uniform fine equiaxed crystal morphology. The mean value of Charpy impact energy at -60 ℃ was about 280 J, and the lowest value was more than 200 J. The low temperature impact toughness was excellent. Under high heat inputs, the metals of thas-deposited component failed to undergo completely intrinsic heat treatment, incomplete recrystallization zone appeared in the structure, and a small amount of coarse columnar structures of the original sedimentary state was remained. At -60 ℃, the mean value of Charpy impact energy was below to 100 J, and the lowest value was only 9 J. The dispersion of the value of Charpy impact energy under high heat inputs was large and the impact toughness was unstable. The value of impact energy was related to the microstructure near the notch of the sample. When the notch was just opened in the complete recrystallization zone, the value of the impact energy was very high, forming a typical ductile fracture. When the notch was opened in the incomplete recrystallization zone, the impact energy is very low, as a brittle fracture. In order to ensure excellent low temperature impact toughness, submerged arc additive manufacturing needed appropriate heat input, and too high heat input leaded to incomplete recrystallization between layers, which was the root cause of deterioration of its low temperature toughness.
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