Hot compression tests of low carbon steel were carried out on Gleeble-3500 system in the temperature range from 750 to 900 ℃ and in the strain rate range from 0.001 to 1.0 s^-1, and the associated microstructural evo...Hot compression tests of low carbon steel were carried out on Gleeble-3500 system in the temperature range from 750 to 900 ℃ and in the strain rate range from 0.001 to 1.0 s^-1, and the associated microstructural evolution was studied by observations with a metallographic microscope. The results show that the stress-strain curves exhibit a peak stress at critical strain, after which the flow stresses decre.ase monotonically until reaching high strains, showing a dynamic flow softening. The peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation. The flow stress increases with increasing strain rate and decreasing deforming temperature. The flow stress can be described by constitutive equation in hyperbolic sine function and can also be described by a Zener-Hollomon parameter Z. With increasing deformation temperature and deereasing strain rate, the grain size as well as the volume fraction of the reerystaUized grains increase. The safe region for hot working of the alloy has been determined according to the processing map and microstructure at the true strain of 0.5, which is the deformation temperature of 840-940 ℃ and the strain rate of 0.001-1.0 s^-1.展开更多
The mechanical properties of calcium(Ca) microalloyed 24 carat gold(Au 99.9 Ca 0.1) were measured and the corresponding microstructure was observed by TEM in order to investigate the strengthening mechanism.It was obs...The mechanical properties of calcium(Ca) microalloyed 24 carat gold(Au 99.9 Ca 0.1) were measured and the corresponding microstructure was observed by TEM in order to investigate the strengthening mechanism.It was observed that the microalloying of 0.1wt% Ca improved the tensile strength(by 79% and 57% for the rolling and annealing states,respectively),hardness and E-Modulus as well as reduced the ductility of the 24 carat Au.Dispersed nano-sized precipitates and high density deformation twins were found in the rolled Au 99.9 Ca 0.1,which are attributed to be the major strengthening factors.The twins subsided after annealing and the strengthening of the annealed Au 99.9 Ca 0.1 is mainly contributed by the coarsened semi-coherent precipitates.展开更多
A novel design scheme of hot stamping, quenching and partitioning process was conducted in a quenchable boron steel to obtain the nanometric duplex microstructure comprising ultrafine retained austenite and martensite...A novel design scheme of hot stamping, quenching and partitioning process was conducted in a quenchable boron steel to obtain the nanometric duplex microstructure comprising ultrafine retained austenite and martensite. It is shown that the materials possess excellent mechanical properties and the ductility can be further improved without compromising the strength. The newly treated steel shows excellent mechanical properties and the total elongation of the steel increases from 6.6% to 14.8% compared with that of hot stamped and quenched steel. Therefore, this kind of steel has become another group of advanced high-strength steels. The microstructure which is mainly responsible for such excellent mechanical properties was investigated.展开更多
基金Funded by North University of Chinathe National Natural Science Foundation of China(Nos.51174251,51201154)the Natural Science Foundation of Shanxi Province,China(No.2013011014-1)
文摘Hot compression tests of low carbon steel were carried out on Gleeble-3500 system in the temperature range from 750 to 900 ℃ and in the strain rate range from 0.001 to 1.0 s^-1, and the associated microstructural evolution was studied by observations with a metallographic microscope. The results show that the stress-strain curves exhibit a peak stress at critical strain, after which the flow stresses decre.ase monotonically until reaching high strains, showing a dynamic flow softening. The peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation. The flow stress increases with increasing strain rate and decreasing deforming temperature. The flow stress can be described by constitutive equation in hyperbolic sine function and can also be described by a Zener-Hollomon parameter Z. With increasing deformation temperature and deereasing strain rate, the grain size as well as the volume fraction of the reerystaUized grains increase. The safe region for hot working of the alloy has been determined according to the processing map and microstructure at the true strain of 0.5, which is the deformation temperature of 840-940 ℃ and the strain rate of 0.001-1.0 s^-1.
基金carried out with the partial financial support of Lao Feng xiang Co.Ltd.
文摘The mechanical properties of calcium(Ca) microalloyed 24 carat gold(Au 99.9 Ca 0.1) were measured and the corresponding microstructure was observed by TEM in order to investigate the strengthening mechanism.It was observed that the microalloying of 0.1wt% Ca improved the tensile strength(by 79% and 57% for the rolling and annealing states,respectively),hardness and E-Modulus as well as reduced the ductility of the 24 carat Au.Dispersed nano-sized precipitates and high density deformation twins were found in the rolled Au 99.9 Ca 0.1,which are attributed to be the major strengthening factors.The twins subsided after annealing and the strengthening of the annealed Au 99.9 Ca 0.1 is mainly contributed by the coarsened semi-coherent precipitates.
基金Funded by the School Foundation of North University of Chinathe National Natural Science Foundation of China(Nos.51206081,51571141)+3 种基金Science and Technology Innovation Project of Shanxi Province(No.2016156)China Postdoctoral Science Foundation(No.2016M590214)Key Research and Development Program of Shanxi Province(No.201603D121002-3)the Natural Science Foundation of Shanxi Province,China(Nos.2015011036,2014011024-6)
文摘A novel design scheme of hot stamping, quenching and partitioning process was conducted in a quenchable boron steel to obtain the nanometric duplex microstructure comprising ultrafine retained austenite and martensite. It is shown that the materials possess excellent mechanical properties and the ductility can be further improved without compromising the strength. The newly treated steel shows excellent mechanical properties and the total elongation of the steel increases from 6.6% to 14.8% compared with that of hot stamped and quenched steel. Therefore, this kind of steel has become another group of advanced high-strength steels. The microstructure which is mainly responsible for such excellent mechanical properties was investigated.
