| 摘要 |
PROBLEM TO BE SOLVED: To provide a glow plug having a chromate coating covering the surface of a main metal containing small quantity of hexavalent chromium and excellent in corrosion resistance and heat resistance as compared with a conventional one, and a manufacturing method thereof. SOLUTION: Surface of a main metal is covered with a chromate coating of 0.2-0.5μm thick where trivalent chromium occupies 95 wt.% or more of chromium component. Since the chromate coating is made thick as compared with conventional trivalent chromium based chromate coating of about 0.1μm thick, corrosion resistance is enhanced significantly and a sufficient durability against corrosion can be imparted to the main metal. Furthermore, corrosion resistance of the main metal can be sustained sufficiently even in the inherent environment of glow plug susceptible to easy temperature rise and acid attack. Chromate treating bath where a trivalent chromium salt is mixed with a complexing agent for trivalent chromium is preferably employed.
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