Cementation process for low alloy steels - with a pre-cementation step in an atmos. for forming a hypereutectoid hardening, then cementation of nuclei formed

摘要

Method for the cementation of low alloy steels having a carbon content =0.5% consists of (a) pre-cementation of the steel in a cementation atmosphere having a carbon potential Acm for producing a cemented envelope having a hypereutectoid compan, (b) cooling the steel to transform the envelope into a bainitic pearlitic or martensitic structure, and (c) cementation of the steel by heat treating it for long enough to produce carbides in a spheroidal form using the carbides of the bainite or the pearlite as nuclei or dissolving the martensite by heating to produce a carbide particles and using these as nuclei. The cementation is effected in such a manner that the rate of heating of the steel is controlled at 20 degrees C/min. from the Ac. temp. to 750-950 degrees C, the carbon potential in the atmosphere being maintained at above Acm when the temp. is AC1. Steels contg. 2.4% Cr having spheroidal carbides can be obtd. occupying 30% of the volume in the region between the surface of the envelope and 0.4 mm deep into the envelope.