Sinter-Alloying and Properties of Manganese Steels – State of the Art pp. 171-233
Authors: Andrej Šalak, Marcela Selecká, Institute for Materials Research of Slovak Academy of Sciences, Watsonova, Košice, Slovak Republic
Abstract: Manganese is the cheapest alloying element with high hardening effect commonly used in wrought steels. Nevertheless, manganese was as an alloying element studied in powder metallurgy since ~1948 mainly under laboratory conditions. The hard reducibility of Mn oxides due to high affinity of manganese for oxygen, especially of MnO, requiring the purity of the sintering atmospheres not attainable in practice, is regarded for a technical problem. In this chapter are given the data (oxygen partial pressure, dew points of the atmosphere) required for the thermodynamic equilibrium conditions for Mn – O system. Presented mechanical and other properties of manganese steels attained prove successful sintering. The used sintering atmospheres for these steels did not fulfill the thermodynamic requirements for the purity. Material and processing factors applied are summarized. Some representative maximal tensile strength values attained are presented. High vapor pressure characterizes manganese, and its values in dependence on temperature are presented demonstrating in a spontaneous sublimation. Effect of manganese vapor on sintering process and alloying of iron powder matrix in the compacts is explained. The reaction of gaseous manganese with the oxygen in the atmosphere is characterized. The result of this is the reduction, (“selfcleaning/ protection”) effect of manganese for H2O in sintering atmosphere to equilibrium conditions for Mn – O system. This process, given by physical property of manganese, is only possible to ensure the effective sintering of manganese containing steels without other special measures.