Laser & Optoelectronics Progress, Volume. 56, Issue 21, 211402(2019)

Microscopic Characteristic Analysis and Crack Suppression of Laser-Surface Remelting of Vermicular-Graphite Cast-Iron Valve Seats

Ming Pang* and Wendan Tan
Author Affiliations
  • Airport College, Civil Aviation University of China, Tianjin 300300, China
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    Experiments on the laser-surface remelting of vermicular-graphite cast-iron valve seats are performed in this study using a Nd∶YAG solid-state laser with a rated power of 3 kW. The macroscopic morphology, microstructure, hardness distribution, and cracks of the remelting layer of the laser-surface remelting of the vermicular-graphite cast-iron valve seats are analyzed using a scanning electron microscope, microhardness tester, and phosphor flaw detection method. The results show that after the surface of the vermicular-graphite cast-iron valve seats is remelted using a laser, the dendritic structures appear in the central region of the remelting layer and the needles and granules are dispersed among the dendritic structures. The morphology of the interface between the remelting layer and substrate is serrated, and the bivalve structure of the martensite and ledeburite shells is observed in the heat-affected zone because of factors such as the diffusion of graphite reducing the melting point of the material in the vicinity of the graphite and rapid heating and cooling of the laser. The hardness from the remelting-zone surface to the substrate gradually decreases because of the differences in the heating and cooling rates in the different regions of laser remelting of the valve seats. The cracks in the laser remelting layer of the valve seats can be restrained by adjusting the laser parameters. A remelting layer without cracks on the surface of the vermicular-graphite cast-iron valve seats of laser remelting can be obtained under the laser remelting process with parameters of laser power P=500 W, defocusing amount Δf=-1 mm, and laser scanning velocity V≤5 mm/s.

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    Ming Pang, Wendan Tan. Microscopic Characteristic Analysis and Crack Suppression of Laser-Surface Remelting of Vermicular-Graphite Cast-Iron Valve Seats[J]. Laser & Optoelectronics Progress, 2019, 56(21): 211402

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    Paper Information

    Category: Lasers and Laser Optics

    Received: Feb. 20, 2019

    Accepted: May. 5, 2019

    Published Online: Nov. 2, 2019

    The Author Email: Pang Ming (pangming1980@126.com)

    DOI:10.3788/LOP56.211402

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