Precipitation Behavior on Carbon Steel Modified by Double Glow Plasma Surface Alloying with W and Mo

Abstract

Many brittle precipitates appeared in the alloyed layers which were formed in surface modified carbon steel by DGPSA (Double Glow Plasma Surface Alloying) with W and Mo because of the slow cooling rate in the alloying furnace. As a result, the mechanical properties of these alloys were significantly degraded by precipitation of the brittle phase. Phase analysis of the electro-extracted precipitates by X-ray diffraction (XRD) revealed that they were mainly composed of the μ-phase and a small amount of carbide, M₆C . In the present study, their microstructures were characterized by optical microscopy (OM) and scanning electron microscopy (SEM). It was concluded that the chemical components, temperature and time were the main thermodynamic factors influencing their deposition. The isothermal transformation (IT) diagram of the precipitates showed that there were two transforming climaxes. Based on the IT diagram, a technique was developed to depress the precipitate deposition.