Influence of alloying elements on Ni distribution in PM steels

Abstract

Powder metallurgical (PM) steels with elemental Ni additions exhibit non-homogenous microstructures with soft Ni rich areas, lean in C, after conventional sintering. Though, the exact correlation between the distribution of Ni and mechanical properties is not well known and depends on the conditions, e.g. the load state, it is desirable to be able to control the distribution of Ni since it plays a major role in the properties of Ni PM components. By introducing other alloying elements, the microstructure homogeneity of Ni containing PM steels, can be influenced. Thus, the effect of common alloying elements on the homogeneity of sintered microstructures has been investigated in the present work. It is found that additions of either C or Mo have minor effect on Ni distribution in the Fe–Ni system. However, addition of both C and Mo to Fe–Ni improves the Ni distribution. In addition, a strong interaction between Ni and Cu is observed and it enhances the Ni homogeneity. Furthermore, the influence of Cu is more pronounced in presence of C.

Keywords:

• Sintering
• Powder metallurgy
• Steels
• Alloying
• Homogeneity

Acknowledgements

The authors would like to thank Höganäs AB for financial support and opportunity to use the research facilities. The authors are grateful to Ola Litström for useful discussion and Marja Haglund for assistance with SEM–EDX analysis.