CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119(b) to Japanese Application No. 2019-085480 filed Apr. 26, 2019, and Japanese Application No. 2019-175020 filed Sep. 26, 2019, the disclosures of which are incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an exhaust system for an engine.

(2) Description of Related Art

In a conventional exhaust system for an engine, the generation of red rust due to exhaust heat in the exhaust passage component can be prevented by a rustproof resin film. However, in a case where the exhaust passage component is fastened to other parts, when the pressure receiving surface that receives the fastening force of the fastener is covered with the rustproof resin film, the plastic deformation of the rustproof resin film may greatly reduce the fastening force of the fastener.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an exhaust system for an engine in which a fastening force of a fastener hardly decreases.

In the present invention, an oxide film of triiron tetraoxide is formed on a pressure receiving surface of an exhaust passage component.

According to the present invention, a fastening force of a fastener (2) is less likely to decrease. Further, the generation of red rust due to exhaust heat on a pressure receiving surface (1a) of an exhaust passage component (1) is prevented.

