Papers by Author: Xiao Ling Yang

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Authors: Xin Zhao, Xiao Ling Yang
Abstract: A new kind of die steel, WD1 used for warm work dies, was developed. The behavior of carbide dissolution and precipitation in WD1 steel during heat treatment was investigated by using optical microscopy, X-ray diffractometer and transmission electron microscopy. The results show that there are three types of carbide, namely MC, M6C and M7C3 carbide, in the annealed WD1 steel; and M6C and M7C3 carbides are dissolved totally during heating for quenching; then MC, M2C, M6C and M7C3 carbides are precipitated during tempering. The secondary hardening peak is reached after tempering at 520°Cfor two hours. This hardening is mainly caused by the precipitation of Mo2C carbide.
1009
Authors: Xin Zhao, Xiao Ling Yang, Tian Fu Jing
Abstract: The warm deformation behavior of as-quenched and as-annealed ASTM 1045 steel was studied by isothermal compression testing on a Gleeble3500 machine. The temperature range was 550-700°C and the strain rate range 0.001-0.1s-1. Transmission electron microscopy (TEM) was used to study the microstructures associated with the observed deformation phenomenons. The results show that the flow stress of quenched specimens is higher than that of annealed ones at 550°C when strain rates are greater than 0.001s-1. However, at 600-700°C and strain rate of 0.001s-1, the whole flow curves of quenched specimens are below that of annealed ones. Under the rest conditions, the flow stress of quenched specimens is higher at the beginning of compression and then the opposite is true after the strain is greater than a critical value. The microstructure examination proves that the dynamic recrystallization easily occurs in quenched specimens during warm compression, which results in the above phenomenons. Keywords: warm deformation, flow stress, steel, quenching, annealing
147
Authors: Xin Zhao, Xiao Ling Yang
Abstract: A new kind of die steel, WD1 used for warm work dies, was developed. The secondary hardening behavior and its affecting factors were studied. The results show that the secondary hardness increases with the content of C, Mo and V elements and Si element can significantly improve the secondary hardening effect though it’s not one of secondary hardening elements. The hardness of WD1 steel tempered at 520°C is more than HRC60, which can meet the requirements of warm work dies.
369
Authors: Xin Zhao, Xiao Ling Yang
Abstract: Gray iron was hot-compressed on a Gleeble 3500 machine. The effect of hot compression on mechanical properties of gray iron was studied. The result shows that gray iron with the sandwich structure of graphite and ferrite matrix is prepared after more than 45% reduction of hot compression. The mechanical properties of 80% hot-compressed gray iron are significantly enhanced: tensile strength from 117MPa to 249MPa, and total elongation from 0 to 5.2%. The tensile fracture surface presents ductility characters after more than 45% reduction of hot deformation. The increase of the strength and ductility of the hot-compressed gray iron is caused by delamination toughening.
1080
Authors: Xin Zhao, Xiao Ling Yang
Abstract: This paper analyzed the microstructure evolution and grain-refining mechanism in producing ultra-fine grained steel sheet by heavy rolling of lath martensite. The results show that this technique is composed of three processes with different grain-refining mechanism respectively: i) austenite grains subdivide into homogeneous and tiny martensite laths during quenching; ii) martensite laths are thinned and damaged during heavy rolling; iii) equiaxed ultra-fine ferrite forms during low temperature recrystallization annealing.
1701
Authors: Xin Zhao, Xiao Ling Yang, Tian Fu Jing
Abstract: Specimens of medium carbon steel were quenched and warm-compressed on a Gleeble 3500 Machine. The microstructure of the specimens was studied by using an optical microscope and a transmission electron microscopy. And the properties were investigated by using tensile tests and hardness tests. Results show that the starting microstructure is lath martensite with a small amount of flake martensite. After 50% compression at 550-650°C, ultrafine grains can be observed in the specimens. The microstructure of the specimens compressed at 600°C is equiaxed ultrafine ferrite grains + nano-carbides and a good combination of strength and ductility is obtained. The tensile strength and total elongation are 861MPa and 19.1%, respectively. The hardness is 233.81Hv.
205
Authors: Xin Zhao, Xiao Ling Yang
Abstract: Steel plates with lath martensite microstructure were rolled up to 68% reduction at 673 K and then annealed at 473-973 K. The microstructure evolution was studied by using an optical microscope and a transmission electron microscopy. And the properties were investigated by using tensile tests and hardness tests. Results show that ultrafine grains + nano-carbides are obtained in the steel plates. The specimen annealed at 823 K has a good combination of strength and ductility. The tensile strength and total elongation are 1028 MPa and 7.2%, respectively. And the hardness is 338 Hv.
863
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