On microstructures and properties of laser modified roller materials

Laser treatment, using a continuous wave CO₂ crosscurrent laser with generated beam power of 1 kW, was performed on the roller samples of the adamite steel and the indefinite chilled cast iron, two of which are in commercial use. Optical microscopy, scanning electron microscopy (SEM) and micro-Vickers hardness tester were used to reveal the microstructural details and mechanical properties of the laser treated zones. The results indicate that, laser treated zones of the two roll samples consist of melted zone, phase transformation zone, heat affected zone and original microstructural zone. After laser treatment, the melting zone appears to have lower hardness compared to the phase transformation zone, but after tempering of the two samples at 540°C for 1 h, the hardness of the melting zones increases differently due to the formation of the fresh martensite from the retained austenite. In contrast, the hardness of the phase transformation zone decreases sharply as fresh martensite has changed to tempered martensite with lower carbon super-saturation. Several hot tears formed in the melting zone of the indefinite chilled cast iron sample, but no in the adamite steel.