A silent chain is provided which has reduced elongation based on wear and which is capable of maintaining a high accuracy over a long period of time in use. The inner surfaces of pin holes formed in at least joint trains of plates have been subjected to shaving, and a hard layer of at least one hard metal carbide selected from a group including CrC, TiC, VC and NbC, is formed on the surface of each pin. By shaving the inner surface of each pin hole, the surface pressure applied between the pin hole inner surface and the pin inserted therein becomes lower, whereby the wear of the pin and the pin hole is diminished. Further, since the hard layer on the pin surface is very hard and is chemically stable, the affinity of each plate for the inner surface of each pin hole formed therein is small. Thus, even under the condition of boundary lubrication, it is difficult for adhesion to occur between the pin hole inner surface and the pin inserted therein. Consequently, the amount of pin wear is lessened so that it becomes possible to minimize the elongation of the chain based on wear.

The work-performing member for a farm machine has a cutting edge made of a high-carbon steel containing graphite in structurally free state in an amount of 0.5 to 1.32 percent of the total mass of the material.

A method of case hardening ferrometallic parts that avoids the use of protective coatings or shields is provided. The process comprises the steps of a) carburizing the entire part, b) machining the carburized part to form first and second surface regions wherein the second surface region has a carbon content at least 100% greater than the carbon content of the first surface region, c) heating the machined part at a hardening temperature with the entire part in contact with a gaseous atmosphere containing a source of carbon and a carbon content of from 85% to 115% of the carbon content of said first surface region, and d) quenching the part.

A method for producing chromium carbide coatings on steel provides a steel component having a surface which is carburized to contain at least about 0.40% by weight carbon and is followed by chromizing the surface to form a chromium carbide coating on the surface.

A chain which does not generate hydrogen brittleness is formed with components having improved wear resistance. At least one part of the chain, for example a surface, is covered with a diamond-like amorphous carbon coating (DLC). Further, metallic particles are dispersed into the diamond-like amorphous carbon coating.