Plasma or ion carburizing of several steels

Abstract

Several carburizing steels, AISI 1020, 4620 and 8620, were plasma carburized in a 5vol.%CH 4-95vol.%H 2 gas mixture at a total pressure of 10 Torr in the temperature range 850 – 1025 °C for various times. In order to reduce the carbon concentration at the surface to an acceptable level, the plasma carburizing stage was followed by a diffusion anneal step. The effects of process variables, time and temperature were examined by using microhardness depth correlations, optical metallography and transmission electron microscopy. The carburized depths were found to be linearly dependent on the square root of the carburizing time for all three steels investigated. The activation energies for plasma carburizing were calculated for AISI 1020, 4620 and 8620 steels as 15 700 cal mol -1, 12 800 cal mol -1 and 11 500 cal mol -1 respectively.