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 properti...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 M_(23)C_6 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.展开更多
Alloy 690 is a typical Ni-Cr-Fe alloy, which is widely used in nuclear power application. However, filler metal 52M （FM-52M） used in alloy 690 weldment is fimnd to be susceptible to ductility-dip cracking （DDC） , ...Alloy 690 is a typical Ni-Cr-Fe alloy, which is widely used in nuclear power application. However, filler metal 52M （FM-52M） used in alloy 690 weldment is fimnd to be susceptible to ductility-dip cracking （DDC） , which seriously affects safety and life extension in nuclear application. In this paper, the DDC susceptibility of FM-52M in welding process was investigated using finite element method. At first, Gleeble-based testing technique, strain to fracture （ STF ） test, was used to evaluate the DDC susceptibility and the formation mechanism of DDC was explained. The result shows that FM-52M is most susceptible at 1 050 ℃ and grain boundary weakness at high temperature induces crack initiation. Afterwards, in order to evaluate the DDC susceptibility under complex stress state, tube-plate welding model was built by means of ABAQUS software. Susceptible regions could be confirmed associated with STF results. The simulation result shows that HAZ is the most susceptible region in FM-52M joint.展开更多
基金financially supported by the National Key Research and Development Program of China (2016YFE0105200)Key Research Program of Frontier Sciences,Chinese Academy of Sciences (QYZDY-SSW-JSC012)
文摘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 M_(23)C_6 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.
文摘Alloy 690 is a typical Ni-Cr-Fe alloy, which is widely used in nuclear power application. However, filler metal 52M （FM-52M） used in alloy 690 weldment is fimnd to be susceptible to ductility-dip cracking （DDC） , which seriously affects safety and life extension in nuclear application. In this paper, the DDC susceptibility of FM-52M in welding process was investigated using finite element method. At first, Gleeble-based testing technique, strain to fracture （ STF ） test, was used to evaluate the DDC susceptibility and the formation mechanism of DDC was explained. The result shows that FM-52M is most susceptible at 1 050 ℃ and grain boundary weakness at high temperature induces crack initiation. Afterwards, in order to evaluate the DDC susceptibility under complex stress state, tube-plate welding model was built by means of ABAQUS software. Susceptible regions could be confirmed associated with STF results. The simulation result shows that HAZ is the most susceptible region in FM-52M joint.
