Browsing by Author "Kuo, IC"

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Effect of aging treatment on the mechanical properties of C-250 maraging steel by flow forming
(2003-02-01)
Lee, IK
;
Chou, CP
;
Cheng, CM
;
Kuo, IC
;
機械工程學系
The technique of forward flow forming has been used to produce a long, thin walled tube made of C-250 maraging steel. The forward flow forming can save raw material, increase strength, and reduce the production process time. Because the work hardening effect on solution-treated C-250 using flow forming is minimal, the flow-formed tube requires an additional heat treatment to obtain higher hardness and strength. With the direct aging treatment, low elongation values are obtained, making this treatment unsuitable for the engineering design. It was found that the 540 degreesC/6 h/AC over-aging treatment results in better strength and elongation values. The strengthening phase of the flow-formed C-250 maraging steel was found to be the intermetallic compound of Fe3Mo.
Effect of heat treatment on microstructures of flow formed C-250 maraging steel
(2003-11-01)
Lee, IK
;
Chou, CP
;
Cheng, CM
;
Kuo, IC
;
機械工程學系
The technique of forward flow forming has been used to produce a long thin walled tube of C-250 maraging steel. Forward flow forming can conserve material, increase strength and reduce production process time. Since the hardness of solution treated C-250, using flow forming, can be increased by approximately 16.2%, flow formed tube must be given an additional aging treatment to increase hardness and strength. Direct aging treatment yields low elongation, which is not suited to design requirements. Using a homogenisation treatment, the microstructure of C-250 was of coarse grained lath type on aging and of needle type after solution treatment and aging. These treatments resulted in low tensile strength, and tensile fracture showed a tendency to brittleness. A 'solution + aging' treatment yielded greater strength and elongation.
Effect of stress relief on microstructure and mechanical properties of flow formed maraging steel weldment by electron beam welding
(2003-06-01)
Lee, IK
;
Chou, CP
;
Cheng, CM
;
Kuo, IC
;
機械工程學系
The technique of forward flow forming has been used to produce a long and thin wall tube of C-250 maraging steel. The work hardening effect of solution treated C-250 by flow forming is small. Therefore aging treatment after flow forming is required to increase hardness and strength. Final formed C-250 tubes are usually manufactured by combining aging treatment and electron beam welding (EBW). The hardness and tensile strength of aged C-250 maraging steel weldment decreased to the corresponding values obtained in the solution annealed state. Thus, the formed tube by EBW requires stress relieving treatment (and similarly for the aged condition) to increase hardness and strength and thus meet the required specification. The strength requirement was successfully achieved but the elongation of the aged, EBW, and stress relieved specimen was 88.5% lower than that of the unwelded specimen. (C) 2003 IoM Communications Ltd. Published by Maney for the Institute of Materials, Minerals and Mining.