Microstructural characterization and wide temperature range mechanical properties of NiCrMoV steel welded joint with hea
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a Liu Shanghai Turbine Plant of Shanghai Electric Power Generation Equipment Co. Ltd., Shanghai 200240, People’s Republic of China; and Department of Mechanical Engineering, Tsinghua University, Beijing 100084, People’s Republic of China
Peng Wang Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China; and Shanghai Turbine Plant of Shanghai Electric Power Generation Equipment Co. Ltd., Shanghai 200240, People’s Republic of China
Qingjun Wu and Haichao Cui Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China
Xin Huo Shanghai Turbine Plant of Shanghai Electric Power Generation Equipment Co. Ltd., Shanghai 200240, People’s Republic of China (Received 29 March 2015; accepted 18 May 2015)
NiCrMoV steels used in nuclear rotor with heavy section were successfully fabricated by ultra-narrow gap submerged arc welding method. In this study, the mechanical properties including the tensile and impact toughness of the welded joints (WJs) with a wide temperature range were systematically investigated. Microstructural characterization indicated that the high-temperature tempered martensite and tempered bainite, as the main microstructure in WJ, were responsible for the improved comprehensive mechanical properties of the WJ. Microhardness across the WJ was measured as well, showing that the highest value of hardness occurred at the heat-affected zone which represents the appropriate lowest impact toughness of WJ. However, compared with the base metal, the ultimate tensile strength of the WJ displayed approximately equivalent values, while the yield strength was increased with increasing temperature. All the fracture of the WJ specimens occurred on the weld metal. In addition, the Charpy impact energy of weld metal was obtained at various temperatures, and the transition temperature (Tt) of welded metal was determined as 5 °C, which helps for the application design. The fractography indicated that the ductile fracture modes changed to quasi-cleavage ones gradually with decreasing temperature, and also the dimples became smaller and shallower.
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.162
requirements of the nuclear rotor materials.4,5 However, being limited by the large size and heavy section of nuclear rotor, it is difficult to manufacture high quality and uniform rotor by forging directly. On the contrary, the practical production to manufacture the combined rotor via appropriate joining method is considered to be an effective approach to meet the necessity. Generally, some common fusion welding methods,6–10 advanced friction stir welding techniques,11–14 and other particular welding methods15 can be used to join steels with large thickness at appropriate filler metals (FM
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