Laser hardening of low-alloyed PM steels

Abstract

The good results obtained by laser-hardening of high-strength P/M steels drove to extend the research to low-alloy material (Fe-Cu-C; 6,6 g/cm3 density). Process conditions have been selected on the basis of previous results. To avoid carbon loss, observed on previous tests, the samples have been also protect-ed, by neutral atmosphere, during any critical step. The microstructural features of the laser hardened Cu-C P/M steels have been analyzed by LOM, whereas the surface micro-geometry has been characterized by SEM. Hardened depth (HD), hardened width (HW) and hardened area (HA) have been measured. 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 hard-ened fully dense steels, has been observed also on low-alloy sintered steels. The addition of a protective atmosphere has been helpful to control decarburization of thin surface layers or surface oxidation. The re-search confirm that Laser transformation Hardening (LTH) is a suitable process to get hard, wear resistant surface, or defined spots on P/M components. The short heating time and the modest volume fraction structurally modified can contribute to avoid part distortion, in comparison with induction hardening. The possibility of very selective and precise hardening treatment has been confirmed. The results of the re-search open new possibilities to widen the use of high-property P/M parts, based on low-alloy materials, for wear-resistant and high precision applications

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