| 摘要 |
A method for producing a selectively surface hardened cast iron part includes the steps of (a) heating the part to a desired austempering temperature of between about 450 DEG F. and about 800 DEG F. until the entire cast iron part possesses the desired austempering temperature substantially uniformly throughout it; (b) heating only the surface of the cast iron part to an austenitizing temperature of between about 1500 DEG F. and about 1800 DEG F. by immersing the cast iron part in a molten lead or tin bath until a desired thickness of an austenite layer is formed on the surface of the cast iron part, without substantial heating of the interior of the cast iron part; (c) quenching the surface-heated cast iron part in a non-liquid quenching bath atmosphere, i.e. a gaseous atmosphere maintained at the desired austempering temperature, for a time adequate to transform the surface austenite layer to an ausferritic structure; and (d) cooling the cast iron part before bainite is formed in the heat-treated surface layer. In this manner, only the heat-treated surface layer of the cast iron part is hardened, because it is quenched from both sides simultaneously from two sources: self-quenching by the interior of the part, and external quenching by the austempering atmosphere. Typical heating times in step (a) are between about 10 minutes and about 10 hours, and in step (b) are between about 3 seconds and about 10 minutes. The quenching time in step (c) is typically between about 15 minutes and about 8 hours.
|
