| 摘要 |
PROBLEM TO BE SOLVED: To improve corrosion resistance and heat resistance while reducing the content of hexavalent chrome of a film by coating a surface of a main metal fitting outside of an insulator provided outside of a center electrode with a chromate film having a film thickness in a specific range and including a specified weight % of trivalent chrome in the chrome component. SOLUTION: A main metal fitting 1 is made of metal such as carbon steel and formed into a cylindrical shape, and forms a housing for spark plug 100, and has a screw part 7 for fitting an engine block at the peripheral surface thereof. A zinc plating layer 41 for preventing corrosion is formed over the whole of the outer surface of a bedding layer 40 of the main metal fitting 1, and outside thereof is coated with a chromate film 42. The chromate film 42 includes 95 wt.% or more of trivalent chrome in the chrome component thereof, and film thickness is formed at 0.2-0.5μm. This chromate film 42 has remarkably high corrosion resistance and heat resistance, and gives sufficient durability against the corrosion to the zinc plating layer 41, and since content of the hexavalent chrome is restricted small, effect for coping with environment is improved.
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