Improvement of Sintered Steels Properties by Microalloying and Grain Size Decrease

摘要

Microalloyed steels have proved to achieve extraordinary strength values as well as good ductility and toughness, and they are widely used as conventional bulk steels. However, in powder metallurgy these steels have not been developed due to some technological difficulties, like ensuring a uniform distribution of the alloying elements in such a small proportion, ensuring a small austenite grain size prior the austenite/ferrite transformation, and the impossibility of carrying out hot work in the conventional sintering process. The objective of this work consists in transferring the benefits of microalloying to sintered steels. For this purpose, Fe-Nb-C and Fe-Mo-Nb-C sintered steels were produced by adding the alloying elements in two different ways (mix of elemental powders and mechanical alloying) and by two different sintering methods (conventional sintering and modified hot pressing). Porosity, grain size, microstructure and mechanical properties were characterized by means of LOM, SEM and hardness.