Microstructure and impact toughness of 16MND5 reactor pressure vessel steel manufactured by electrical additive manufact
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ORIGINAL PAPER
Microstructure and impact toughness of 16MND5 reactor pressure vessel steel manufactured by electrical additive manufacturing Xi‑kou He1 · Chang‑sheng Xie1,2 · Li‑jun Xiao1 · Ying Luo3 · Di Lu4 · Zheng‑dong Liu1 · Xi‑tao Wang2 Received: 26 March 2020 / Revised: 12 May 2020 / Accepted: 14 May 2020 © China Iron and Steel Research Institute Group 2020
Abstract Electrical additive manufacturing can improve manufacturing efficiency and reduce the cost of 16MND5 reactor pressure vessel steel. Impact tests were conducted to compare the impact toughness of 16MND5 steels manufactured by the electrical additive manufacturing and conventional forging, respectively. It is found that the impact toughness of electrical additive manufacturing specimen was slightly higher than that of conventional forging specimen. The characterizations of microstructure show that there were large ferrites and carbides in electrical additive manufacturing specimen. The fracture mechanisms of electrical additive manufacturing specimen were that microvoids or microcracks were prone to nucleate at the large ferrite/bainite interface and large carbide/bainitic ferrite interface, where the stress concentration was high. In addition, the block size and high-angle grain boundaries played a vital role in hindering crack propagation of electrical additive manufacturing specimen, helping to improve the impact energy and leading to a low ductile–brittle transition temperature. The results suggest that the electrical additive manufacturing technology was an effective method to enhance the impact toughness of 16MND5 steel. Keywords Electrical additive manufacturing · 16MND5 steel · Impact toughness · Fracture · High-angle grain boundary
1 Introduction The reactor pressure vessels (RPVs) are one of the core components of the nuclear island, which operates for long time under the harsh environment of high temperature, high pressure and strong neutron irradiation [1–3]. 16MND5 steel is French vessel steel, which is similar to American SA508 Gr.3 steel. It is commonly used in RPVs due to its high strength, high resistance to irradiation embrittlement and excellent toughness [4–6]. However, the fabrication of * Xi‑kou He [email protected] 1
Institute for Special Steels, China Iron and Steel Research Institute, Beijing 100081, China
2
Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing 100083, China
3
Science and Technology on Reactor System Design Technology Laboratory, Nuclear Power Institute of China, Chengdu 610041, Sichuan, China
4
Southern Additive Science and Technology Co., Ltd., Foshan 528225, Guangdong, China
RPVs by traditional forging processes usually results in the long cycle and low ratio of material utilization. In addition, the traditional forging processes are affected by the cooling rate during the quenching process. With the increase in wall thickness, the cooling rate at 1/2 wall thickness decreases gradually, resulting in uneven microstructures and mech
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