Patent ID: 7628870
Filing Date: 2009-12-08
Classification: C21D,C22C,F01L

Abstract:
1. A method of making a valve guide having enhanced wear resistance when used in an internal combustion engine comprising: (a) Providing an elongated blank of gray cast iron comprising from about 3 to about 3.5 wt. % carbon, about 0.2 wt. % phosphorous maximum, from about 0.35 to about 0.75 wt. % molybdenum, from about 1.8 to about 3 wt. % silicon, from about 0.6 to about 1 wt. % manganese, from about 0.8 to about 1.5 wt. % chromium, balance essentially iron; (b) Machining said blank to form a generally round shape; (c) Forming a center hole along a longitudinal axis of said rounded blank; (d) Heat treating said rounded blank containing said center hole by heating the blank to an austenitizing temperature sufficient to promote formation of austenite and for a time sufficient to dissolve carbon in said austenite, quenching said blank in a quenching medium to form martensite, and the heating said quenched blank to a temperature from about 1000° F. to about 1200° F. to temper said martensite and obtain a microstructure comprising 3% or more molybdenum and chromium intercellular carbides in a matrix of tempered martensite and to obtain a Rockwell C hardness of about 35 to about 45; (e) Machining said heat-treated blank to form a valve guide; and (f) contacting an interior surface of said valve guide against a valve stem having a hardness greater than that of said valve guide so that when said valve stem is contacted and passed against said valve guide interior surface, wear on said valve stem during said contact is minimized.