Surface Characterization in a 300 M Bainitic Steel Laser Carburizing

Abstract

300 M steel was developed from high-strength steel SAE 4340, the goal of this improvement was get better toughness and weldability in applications requiring improved mechanical properties; with small changes in alloy elements, addition of vanadium and especially the silicon content. This work uses low-power laser CO2 (125 W) for introducing carbon into the surface of 300 M steel with bainitic structure. The bainitic microstructure was obtained by isothermal cooling at 300°C for 60 minutes after austenitizing at 850°C for 30 minutes; this heat treatment increased the hardness of 360 HV for 474 HV. The CO2 laser parameters as resolution and power were kept constant and the speed is varied. It was used as carbon black coating to better the absorption of light laser. After surface treatment, the metallographic preparation was carried out and made the observation with optical microscopy. The analysis of the coating showed a speed range in which the levels of hardness layer increased to around 550 HV. In the heat affected zone (HAZ) the hardness introduced himself like bainitic structure of the base material, about 470 HV. The thickness of the compound layer formed on the surface was around 20 μm and the heat affected zone was around 45 μm. It is hoped that this surface treatment could improve the tribological and corrosion resistance properties.