| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 86 === There are two subjects in this study: One is Laser hardfacing cladding, and the other is high frequency induction surface hardening. In the experiments of Laser hardfacing cladding, AISI 4330H were selected as base metal. then cladded with Cobalt-based stellite 6 alloy powder using different process variables to analyze the effects of Laser power, scanning speed, offset and powder deposition on micro region compositions and microstructure. In the experiments of high frequency induction surface hardfacing, AISI 4140 and AISI 4340 were selected as base metal. Then surface hardened with 400KHz frequency to analyze the effects of materials, gap distance, transverse velocity on h ardness, temperature, tensile strength and microstructure.
The results show that: There are three different microstructures int he solidification structure of Laser hardfacing cladding layer. They are equiaxial dendrite, columnar dendrite, and cellular dendrite from surface to the base metal. Their structures are slightly different because of different dilution. The Co, Ni, Si content in dendrite arm is higher than the interdendritic area. The Co content in dendrite arm is about 60%, which is much higher than the interdendritic area, about 45%. The Cr content in the interdendritic area is about 38%, which is higher than in the dendrite arm, about 25%. The Ni content in the dendrite arm is about 2.5%, which is higher than in the interdendritic area, about 1.5%. The W content in the interdendritic area is about 8%, which is higher than in the dendrite arm, about 4.2%. While the Si content is almost zero in the interdendritic area under all the process variables. The Fe content in the interface between cladding and base metal is higher than other area becau-se of dilution.
The keypoint of success of the high frequency induction surface hardening relies on the Austinization and quenching suddenly. The highest hardeness of the surface hardened by high frequency induction can reach Hv 700∼800. The area which possesses the highest hardness is about 0.1∼0.2 mm from surface. And the hardness is higher than the same material hardened by quenching. This phenomenon is related to the fine martensite structure and residual stress in the surface. The higher the surface induction temperature, the harded surface of the metal will be. There are three areas in the fractured surfaces of tensile test specimens. They are surface hardening area, transition area, and base metal from surface to the core of the specimen. The thicker the surface hardening layer, the more obvious these three areas will be. The characteristics of the surface hardening area is fine, shallow dimples. In the transition area, it is a combination of dimples and cleavage structure near the surface hardening area. And obvious cleavage structure near the base metal area. While in the base metal area, there are deepdimples.
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