Process for strengthening nodular cast iron and finished product thereof

Abstract

The invention discloses a process for strengthening nodular cast ion and a finished product thereof. The process comprises the following steps of: putting cleaned nodular cast iron parts into a carburizing furnace; performing carbonitriding, namely adding methanol and ammonia at the temperature of between 800 and 840 DEG C, wherein the addition of the methanol is 80-120 drops / minute, the adding volume of the ammonia is 1 to 5 percent of the volume of the methanol cracked gas, the carbon potential is maintained to between 0.8 and 1.2 percent, and the processing time is 2 to 4 hours; and performing quenching to obtain a part finished product. In the carbonitriding process, the decarbonization preventing technological measure is adopted, the metallographic structure of the finished product comprises a surface layer, a sublayer and a substrate in turn, the surface layer is a granular or continuously distributed compound layer, the sublayer is hidden needle-like nitrogenous martensite, retained austenite and graphite, and the substrate is thin needle-like martensite, retained austenite and graphite. The process can improve the scratch resistance, wear resistance and contact fatigue strength, can effectively prevent full decarbonization during carbonitriding of the nodular cast ion, and has the advantages of low process difficulty and low production cost.

Description

technical field

[0001] The invention relates to a heat treatment process of nodular cast iron, in particular to a nodular cast iron strengthening process and its finished product, which is specifically applied to making parts such as a nodular cast iron rocker arm and a tappet of an engine. Background technique

[0002] The surface strengthening process of ductile iron parts generally only includes the formation of local chill layer, surface quenching, nitriding, nitrocarburizing, surface rolling strengthening and the combination of these processes, such as chill layer quenching, ductile iron crankshaft nitrocarburizing Back fillet rolling strengthening, etc., does not include the carbonitriding process, because the application of the carbonitriding process to ductile iron parts is often considered to be superfluous - the traditional understanding is that nodular cast iron parts are not carburized or carbonitrided Co-infiltration also has sufficient hardenability, and simple...

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