By Chaman Lall, Ph.D., China Metal Powder Vice President – Technology & Applications Development
The soft magnetic properties of Powder Metal (P/M) components are essentially dictated by the level of impurities, the resultant density and the sintering practice. The focus here is on the latter, where the metallurgical structure of the product is developed. High temperature sintering was performed in a walking beam furnace and a vacuum furnace, both capable of operating to a temperature of 1315°C. Test samples were processed in vacuum, dissociated ammonia and pure hydrogen at temperatures ranging from about 1120°C to 1288°C. The effect of these sintering variables on the soft magnetic and mechanical properties of Fe, Fe-0.45%P, Fe-3%Si, Fe-50%Ni, 410L and 434L stainless steels are reported and discussed. These properties are correlated with the nitrogen, oxygen, and dew point levels in the sintering furnace. Additional analysis for carbon, oxygen, and nitrogen was also performed on the sintered product. Furthermore, examples of the resultant microstructures for each of these materials are shown. The optimum properties for soft magnetic performance are obtained by maximizing density and sintering temperatures, and minimizing the contamination levels of carbon, nitrogen and oxygen.
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