Investigação do processo de endurecimento de materiais via laser

Abstract

In this work, the laser hardening process has been investigated using the AISI 1045 steel. The effects of the variables diameter (^f), energy density (Wg) and power density (Wp) of the laser beam, as well as, the environmental atmosphere (room and argon) during irradiation, on the surface hardening, was analyzed for single point and multiple point (trail of points) irradiations. Vickers indentation micro hardness, optical metallography, scanning electron microscopy and X-ray diffraction were utilized for the characterization of the laser beam affected zone. For the single point irradiation it was verified that: the laser affected zone has a spherical cap (shell) shape with dimensions strongly sensitive to laser beam parameters and enviroiunental atmosphere; the hardness measured on surface, as well as along the depth (transversal section of the affected zone), is maximum near the surface and decreases rapidly in the interface between the affected zone and the base metal; the action of laser beam induces a strong increase in the AISI 1045 hardness; from an initial value of 250 HV to maximum values in the range 800-1000 HV; the microestructure of the affected zone is composed of two regions, one, near the surface of irradiated material, characterized by the presence of highly refined martensite, and, another, a transition region, where martensite coexists with proeutectoide ferrite. The investigation performed on multiple point irradiation (trail of points) has given initial information for a better definition of the surface hardening of parts; concerning the laser parameters and the geometry of the pulse distribution on the part surface. Also, a phenomenological equation relating the maximum depth of the laser affected zone, z, with beam parameters was obtained, given by: ^""^ ^~^/A/^V^) where the parameter A depends on the environment atmosphere, and B is only slightly dependent on Wp. With the use of this equation a monogram was constructed, which can be usea for routine surface hardening operations with AISI 1045 carbon steel. This monogram, if enriched with data from others materials, may be eventually used by the laser designer to choose the better range for the laser beam parameters adequate to surface hardening, owing to dedicated, more economical laser equipments.