Effects of hydrogen on the fracture toughness of CrMo and CrMoV steels quenched and tempered at different temperatures |
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| Affiliation: | 1. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China;2. Institute for Special Steels, Central Iron and Steel Research Institute, Beijing 100081, China;1. State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an 710049, China;2. Department of Geosciences, Center for Materials by Design, and Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794-2100, USA;3. School of Chemical Engineering & Technology, China University of Mining and Technology, Xuzhou 221116, China;1. School of Chemical Engineering and Technology, Xi''an Jiaotong University, Xi''an 710049, China;2. State Key Laboratory of Multiphase Flow in Power Engineering, Xi''an Jiaotong University, Xi''an 710049, China;3. East China Design Institute of China Petroleum Engineering Construction Co., Ltd., Qingdao 266580, China;4. Lanzhou LS Heavy Equipment CO., LTD, Lanzhou 730300, China;1. Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai, Miyagi, 980-8577, Japan;2. Graduate School of Engineering, Tohoku University, Aramaki Aza Aoba 6-6, Aoba-ku, Sendai, Miyagi, 980-8579, Japan;3. Faculty of Science and Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate, 020-8553, Japan;4. Department of Mechanical Engineering, National Institute of Technology, Nagano College, 716 Tokuma, Nagano, 381-8550, Japan;1. Politecnico di Milano, Department of Mechanical Engineering, Via La Masa 1, 20156 Milan, Italy;2. Politecnico di Milano, Chemistry, Material and Chemical Engineering Department “Giulio Natta”, Via Mancinelli 7, 20131 Milan, Italy |
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| Abstract: | Tempering temperatures ranging between 500 and 720 °C were applied in order to analyse the relationship between steel microstructure and the deleterious effect of hydrogen on the fracture toughness of different CrMo and CrMoV steels. The influence of hydrogen on the fracture behaviour of the steel was investigated by means of fracture toughness tests using CT specimens thermally pre-charged with hydrogen gas.First, the specimens were pre-charged with gaseous hydrogen in a pressurized reactor at 19.5 MPa and 450 °C for 21h and elasto-plastic fracture toughness tests were performed under different displacement rates. The amount of hydrogen accumulated in the steel was subsequently determined in order to justify the fracture toughness results obtained with the different steel grades. Finally, scanning electron microscopy was employed to study both the resulting steel microstructures and the fracture micromechanisms that took place during the fracture tests.According to the results, hydrogen solubility was seen to decrease with increasing tempering temperature, due to the fact that hydrogen microstructural trapping is lower in relaxed martensitic microstructures, the strong effect of the presence of vanadium carbides also being noted in this same respect. Hydrogen embrittlement was also found to be much greater in the grades tempered at the lowest temperatures (with higher yield strength). Moreover, a change in the fracture micromechanism, from ductile (microvoid coalescence, MVC), in the absence of hydrogen, to intermediate (plasticity-related hydrogen induced cracking, PRHIC) and brittle (intergranular fracture, IG), was appreciated with the increase in the embrittlement indexes. |
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| Keywords: | Hydrogen embrittlement fracture toughness Quenched and tempered steels Thermally pre-charged specimens Failure micromechanisms |
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