Multi-scale study of ductility-dip cracking in nickel-based alloy dissimilar metal weld
来源期刊：JOURNAL OF MATERIALS SCIENCE TECHNOLOG2019年第4期
论文作者：Yifeng Li Jianqiu Wang En-Hou Han Wenbo Wu Hannu H?nninen
文章页码：545 - 559
摘 要：A ductility-dip-cracking（DDC）-concentrated zone（DCZ） in a width of about 3 mm was observed adjacent to the AISI 316 L/52 Mw fusion boundary（FB） in 52 Mw. The morphology, microstructure, mechanical and thermal properties and corrosion behavior in simulated primary water of DDC/DCZ were investigated by scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, 3 D X-ray tomography（XRT）, 3 D atom probe（3 DAP）, slow strain rate tensile（SSRT） testing and thermal dilatometry. The results indicate that DDCs are random-shaped and disc-like cavities with corrugated structure of inner surface and are parallel in groups along straight high-angle boundaries of columnar grains, ranging from micrometers to millimeters in size. Large-size M23C6 carbides dominate on the grain boundaries rather than MC（M=Nb, Ti）, and thus the bonding effect of carbides is absent for the straight grain boundaries.The impurity segregation of O is confirmed for the inner surfaces of DDC. The oxide film formed on the inner surface of DDC（about 50 nm） is approximately twice as thick as that on the matrix（about 25 nm）in simulated primary water. The yield strength, tensile strength and elongation to fracture of 52 MwDCZ（400 MPa, 450 MPa and 20 %, respectively） are lower than those of 52 Mw-MZ（460 MPa, 550 MPa and 28 %, respectively）. The intrinsic high-restraint weld structure, the additional stress/strain caused by the thermal expansion difference between AISI 316 L and 52 Mw as well as the detrimental carbide precipitation and the resulting grain boundary structure all add up to cause the occurrence of DCZ in the dissimilar metal weld.
Yifeng Li1,2，Jianqiu Wang1，En-Hou Han1，Wenbo Wu1,2，Hannu H?nninen3
1. Key Laboratory of Nuclear Materials and Safety Assessment,Institute of Metal Research,Chinese Academy of Sciences2. School of Materials Science and Engineering,University of Science and Technology of China3. Department of Mechanical Engineering,Aalto University
摘 要：A ductility-dip-cracking（DDC）-concentrated zone（DCZ） in a width of about 3 mm was observed adjacent to the AISI 316 L/52 Mw fusion boundary（FB） in 52 Mw. The morphology, microstructure, mechanical and thermal properties and corrosion behavior in simulated primary water of DDC/DCZ were investigated by scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, 3 D X-ray tomography（XRT）, 3 D atom probe（3 DAP）, slow strain rate tensile（SSRT） testing and thermal dilatometry. The results indicate that DDCs are random-shaped and disc-like cavities with corrugated structure of inner surface and are parallel in groups along straight high-angle boundaries of columnar grains, ranging from micrometers to millimeters in size. Large-size M23C6 carbides dominate on the grain boundaries rather than MC（M=Nb, Ti）, and thus the bonding effect of carbides is absent for the straight grain boundaries.The impurity segregation of O is confirmed for the inner surfaces of DDC. The oxide film formed on the inner surface of DDC（about 50 nm） is approximately twice as thick as that on the matrix（about 25 nm）in simulated primary water. The yield strength, tensile strength and elongation to fracture of 52 MwDCZ（400 MPa, 450 MPa and 20 %, respectively） are lower than those of 52 Mw-MZ（460 MPa, 550 MPa and 28 %, respectively）. The intrinsic high-restraint weld structure, the additional stress/strain caused by the thermal expansion difference between AISI 316 L and 52 Mw as well as the detrimental carbide precipitation and the resulting grain boundary structure all add up to cause the occurrence of DCZ in the dissimilar metal weld.
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