Abstract
Powder metallurgy (PM) offers several variants to introduce alloying elements for establishing the desired final composition. One route is the master alloy (MA) approach. The composition and the elements contained in the MA can be adjusted to obtain a liquid phase that penetrates through the interconnected pore network and thus enhances the distribution of the alloying elements and the homogenization of the microstructure. Such a liquid phase is often of a transient character, and therefore the amount of liquid formed and the time the liquid is present during the sintering are highly dependent on the heating rates. The heating rate has also an impact on the reaction temperatures, and therefore, by properly adjusting the heating rate, it is possible to sinter PM-steels alloyed with Fe-Cr-Si-C-MA at temperatures below 1250 °C. The present study shows the dependence of the melting regimes on the heating rate (5, 10, 20, 120 K/min) represented by “Kissinger plots”. For this purpose, liquid phase formation and distribution were monitored in quenching dilatometer experiments with defined heating up to different temperatures (1120 °C, 1180 °C, 1250 °C, 1300 °C) and subsequent quenching. Optimum sintering conditions for the materials were identified, and the concept was corroborated by C and O analysis, CCT diagrams, metallographic sections, and hardness measurements.
Highlights
Ferrous powder metallurgy (PM) parts production will be challenged in several ways in the near future
The heating rate has an impact on the reaction temperatures, and by properly adjusting the heating rate, it is possible to sinter Powder metallurgy (PM)-steels alloyed with Fe-Cr-Si-C-master alloy (MA) at temperatures below 1250 ◦C
The present study shows the dependence of the melting regimes on the heating rate (5, 10, 20, 120 K/min) represented by “Kissinger plots”
Summary
Ferrous powder metallurgy (PM) parts production will be challenged in several ways in the near future. The raw material cost for Cu [1] and Mo constantly increase—“Molybdenum has increased 19.25 USD/kg or 81.91% since the beginning of 2021” [2]—and the use of Ni [3] is progressively restricted due to health hazards As these are the three alloying elements most commonly used in ferrous PM parts [4,5,6], it is necessary to develop new alloying concepts that can support future industrial needs. In a first step, quenching dilatometer abortion experiments were carried out up to different final temperatures with a fast heating rate (120 K/min) to study the evolution of the melting process and the liquid phase distribution in the specimen at temperature. From these specimens CTT diagrams were recorded and metallographic sections were prepared to verify the method
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