Laser hardening of steel sintered parts

The possibility of applying rapid and localized laser hardening to near-net shape parts, like the ones deriving from powder metallurgy (P/M) is investigated, demonstrating that even low alloyed steels (Fe + 2% Cu + 0,7% C) can be successfully heat treated with minimal or no dimensional variations. Laser hardening conditions have been selected on the basis of the results of the previous research, carried out by means of an Nd-YAG high power system [1]. To avoid some carbon loss, observed on previous activities, the samples have been protected by neutral atmosphere. The microstructural features of the laser hardened steels have been analyzed by optical microscopy, whereas the surface micro-geometry has been characterized by scanning electron microscope. Hardened depth (HD), hardened width (HW) and hardened area (HA) have been measured as well. As expected, the micro-hardness profiles present a sharp drop at low distance from the hardened surface. The typical splitting between hardened zone and heat-affected zone (HAZ), well known from laser hardened fully dense steels, has been observed also on low-alloy sintered steels. The use of a protective atmosphere has been helpful to control surface decarburization and to prevent oxidation. The research confirm that Laser transformation Hardening (LTH) is a suitable hardening process of P/M components, through the action of a scanning laser beam. The short heating time and the modest volume fraction structurally modified can contribute to avoid part distortion, in comparison with other hardening methods.