Effect of Laser Surface Modification and Tempering Process on Microstructure and Hardness Profiles of Roll Materials

Abstract

Laser surface modification, using a continuous wave CO2 crosscurrent laser with generated beam power of 1 kW, was performed on the adamite steel, indefinite chilled cast iron and high speed steel rolls which were applied to the industries. Optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and micro Vickers hardness test were applied to reveal the microstructural details and hardness profiles of the laser treated zone. The results indicate that, laser treated zones of three roll samples consist of melting zone, phase transformation zone and heat affected zone. After laser treatment, the melting zone have low hardness compared to the phase transformation zone, but after tempering at 540°C for 1 hr, the hardness at the melting zone dramatically increases, because of the formation of the fresh martensite from retained austenite. In contrast, the hardness at the phase transformation zone sharply decreases as fresh martensite changed to tempered martensite. There are many small and well distributed FeS and MnS inclusions in the melting zone at the three roll samples.