Spark plug, the metal shell of the spark plug, and a method of manufacturing a spark plug

An object of the present invention is to provide a spark plug which has excellent resistance to stress corrosion cracking resistance, not salt corrosion resistance only. A spark plug is provided with a nickel plating layer, a metal shell coated with a composite layer containing a chromate layer formed on the nickel plating layer. Chromate layer had a thickness of 2～45Nm, the concentration of Cr element is not more than 60at%, containing Ni in addition to Cr. .FIELD 4