Patent ID: 9617632
Date: 2017-04-11
CPC Classifications: C21D,C23C

Claim:
1. A process for surface hardening a workpiece made from an iron, nickel and/or chromium based alloy by gas carburization in which an unsaturated hydrocarbon is contacted with the workpiece inside a carburization reactor under a pressure of about 3.5 to 100 torr and at an elevated carburization temperature to cause carbon to diffuse into the workplace surfaces thereby forming a hardened primary surface layer which is essentially free of carbide precipitates as well as a thermal oxide film, the process further comprising increasing the rate at which carburization occurs by feeding a carbon-free, halogen-containing activating compound to the carburization reactor simultaneously with feeding the unsaturated hydrocarbon to the carburization reactor, wherein the hydrocarbon inside the carburization reactor is about 8 to 35 vol. %, the concentration of the carbon-free, halogen-containing activating compound inside the carburization reactor is about 0.5 vol. % to 3 vol. % and the flow of carbon-free, halogen-containing activating compound being fed to the carburization reactor during carburization is pulsed.