Thermal Treatment of the AISI M2 High Speed Steel Promoted by a CO₂ Laser Beam

The purpose of this paper is the evaluation of the use of a low power CO2 laser beam (50W) to promote the thermal treatment of AISI M2 high-speed steels and evaluate the tribological properties of the graphite coating that takes place on the steel surface after laser irradiation. In order to minimize the steel surface reflection at approximately 90% of the incident radiation wavelength (10.5 μm), an incident radiation absorber layer was applied to the steel surface sample. This coating aims to absorber the incident heat and transfer part of heat to the steel surface. As results the surface presented high hardness and a thin coating of graphite on the surface. The micro-structural changes, occurred on the steels surface, resulting from heat transfer from the absorbing layer, were evaluated through optical microscopy (MO), scanning electron microscopy (MEV), micro-hardness essays (MH), X-ray analysis (XRD), Raman spectroscopy and tribological testers on the graphite coating. MO analysis showed on the transversal section of the heated affected zone a brighter layer than the sample’s core, 30 micrometers thickness, in the surface sample a black coat 10 micrometers thickness. By MH analysis this brighter layer presented hardness approximately 30% superior than the regions without treatment, and by Raman spectroscopy it was evaluated the graphite coating. The XRD analysis on the surface sample reveals an increasing of the martensite and iron-carbide phase. The experimental results of pin-on-disk tests on the graphite coatings reveal a reduced coefficient friction as compared to the original surface.