A unit cell including the matrix, precipitation free zone(PFZ) and grain boundary was prepared, and the crystal plasticity finite element method(CPFEM) and extended finite element method(XFEM) were used to simulate th...A unit cell including the matrix, precipitation free zone(PFZ) and grain boundary was prepared, and the crystal plasticity finite element method(CPFEM) and extended finite element method(XFEM) were used to simulate the propagation of cracks at grain boundary. Simulation results show that the crystallographic orientation of PFZ has significant influence on crack propagation, which includes the crack growth direction and crack growth velocity. The fracture strain of soft orientation is larger than that of hard orientation due to the role of reducing the stress intensity at grain boundary in intergranular brittle fracture. But in intergranular ductile fracture, the fracture strain of soft orientation may be smaller than that of hard orientation due to the roles of deformation localization.展开更多
Characteristic HSLA steels for automotive use are introduced in which both of precipitation and microstructure is controlled to obtain suitable mechanical properties.For outer panels such as fender,the combination of ...Characteristic HSLA steels for automotive use are introduced in which both of precipitation and microstructure is controlled to obtain suitable mechanical properties.For outer panels such as fender,the combination of low yield strength,high tensile strength and deep-drawability were realized by controlling the distribution of NbC and precipitation free zone.The other steel,developed for chassis parts such as lower arm,utilizes extremely fine interphase precipitation to obtain high yield strength and excellent hole expansionability.Both steels have contributed to the reduction of weight in car body.展开更多
In this study, the precipitation behavior of a new austenitic heat-resistant steel （Fe-20Cr-30Ni-2Nb, in at%） was investigated. The effects of alloying addition of boron （B） and lanthanum （La） on the microstruct...In this study, the precipitation behavior of a new austenitic heat-resistant steel （Fe-20Cr-30Ni-2Nb, in at%） was investigated. The effects of alloying addition of boron （B） and lanthanum （La） on the microstructure of the austenitic steel were scrutinized using SEM, EPMA, TEM, and XRD. The results showed that the addition of B enhanced the precipitation of bar-type Laves phase. A small precipitate with high La concentration was observed at the grain boundary in the alloy without aging; similar precipitates without La also presented in region adjacent to the La single phase. This result indicates that La can exist independently and does not contribute to the formation of new compounds. However, in both B- and La-modified alloy, B appeared in the precipitate free zone. In the alloy containing both B and La, only Fe2Nb Laves- phase precipitates, as indicated by the XRD result.展开更多
The formation of precipitation free zone (PFZ) and its effect in a RSP AI-Li alloy has been studied. The results show that PFZ is easy to form when aged at 190℃,but there is no equilibrium phase on grain boundaries.T...The formation of precipitation free zone (PFZ) and its effect in a RSP AI-Li alloy has been studied. The results show that PFZ is easy to form when aged at 190℃,but there is no equilibrium phase on grain boundaries.The growth of PFZ in the alloy is different from that in conventional AI-Li alloys, The effect of PFZ is of great importance because of its large volume fraction in the alloy.It offsets the beneficial effect of RSP,and is thought to be an important factor that leads to the poor toughness and low ductility of RSP AI-Li alloy sheet.展开更多
基金Projects(51475162,51405153)supported by the National Natural Science Foundation of ChinaProject(14JJ5015)supported by the Hunan Provincial Natural Science Foundation,China
文摘A unit cell including the matrix, precipitation free zone(PFZ) and grain boundary was prepared, and the crystal plasticity finite element method(CPFEM) and extended finite element method(XFEM) were used to simulate the propagation of cracks at grain boundary. Simulation results show that the crystallographic orientation of PFZ has significant influence on crack propagation, which includes the crack growth direction and crack growth velocity. The fracture strain of soft orientation is larger than that of hard orientation due to the role of reducing the stress intensity at grain boundary in intergranular brittle fracture. But in intergranular ductile fracture, the fracture strain of soft orientation may be smaller than that of hard orientation due to the roles of deformation localization.
文摘Characteristic HSLA steels for automotive use are introduced in which both of precipitation and microstructure is controlled to obtain suitable mechanical properties.For outer panels such as fender,the combination of low yield strength,high tensile strength and deep-drawability were realized by controlling the distribution of NbC and precipitation free zone.The other steel,developed for chassis parts such as lower arm,utilizes extremely fine interphase precipitation to obtain high yield strength and excellent hole expansionability.Both steels have contributed to the reduction of weight in car body.
文摘In this study, the precipitation behavior of a new austenitic heat-resistant steel （Fe-20Cr-30Ni-2Nb, in at%） was investigated. The effects of alloying addition of boron （B） and lanthanum （La） on the microstructure of the austenitic steel were scrutinized using SEM, EPMA, TEM, and XRD. The results showed that the addition of B enhanced the precipitation of bar-type Laves phase. A small precipitate with high La concentration was observed at the grain boundary in the alloy without aging; similar precipitates without La also presented in region adjacent to the La single phase. This result indicates that La can exist independently and does not contribute to the formation of new compounds. However, in both B- and La-modified alloy, B appeared in the precipitate free zone. In the alloy containing both B and La, only Fe2Nb Laves- phase precipitates, as indicated by the XRD result.
文摘The formation of precipitation free zone (PFZ) and its effect in a RSP AI-Li alloy has been studied. The results show that PFZ is easy to form when aged at 190℃,but there is no equilibrium phase on grain boundaries.The growth of PFZ in the alloy is different from that in conventional AI-Li alloys, The effect of PFZ is of great importance because of its large volume fraction in the alloy.It offsets the beneficial effect of RSP,and is thought to be an important factor that leads to the poor toughness and low ductility of RSP AI-Li alloy sheet.
