Spark plug, and main metal fitting for spark plug

Abstract

Provided is a spark plug having excellent salt corrosion resistance and stress corrosion cracking resistance. This spark plug comprises a main metal fitting coated with a composite layer which comprises a nickel plating layer and a chromate layer formed on the nickel plating layer, and is characterized in that the nickel plating layer has a thickness (A) of 3 to 15 [mu]m inclusive (3[mu]m <= A <= 15[mu]m) and the chromate layer has a thickness (B) of 2 to 45 nm inclusive (2 nm <= B <= 45 nm).

Description

technical field [0001] The invention relates to a spark plug for an internal combustion engine. Background technique [0002] The spark plug used for ignition of internal combustion engines such as gasoline engines has the following structure: an insulator is provided outside the center electrode, and a main metal case is provided outside the insulator, a ground electrode is installed on the main metal case, and the ground electrode is connected to the ground. A spark discharge gap is formed between the electrode and the center electrode. Usually, the main metal shell is made of iron materials such as carbon steel, and the surface thereof is often subjected to plating treatment for anti-corrosion. As this plating treatment technique, there is known a construction technique of forming a plating layer having a two-layer structure consisting of a Ni plating layer and a chromate layer (Patent Document 1). [0003] Patent Document 1: Japanese Patent Laid-Open No. 2002-184552 ...

AI Technical Summary

Problems solved by technology

Due to the deformation of the main metal shell accompanying this riveting process, there is a problem that cracks and peeling occur on the plating layer, resulting in deterioration of salt corrosion resistance.

In addition, due to the stress remaining in the main metal shell due to the riveting process and the increase in hardness accompanying the structural change caused by t

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