Abstract
Reaching high density in PM steels is important for high-performance applications. In this study, liquid phase sintering of PM steels by adding gas-atomized Ni-Mn-B master alloy was investigated for enhancing the density levels of Fe- and Mo- prealloyed steel powder compacts. The results indicated that liquid formation occurs in two stages, beginning with the master alloy melting (LP-1) below and eutectic phase formation (LP-2) above 1373 K (1100 °C). Mo and C addition revealed a significant influence on the LP-2 temperatures and hence on the final densification behavior and mechanical properties. Microstructural embrittlement occurs with the formation of continuous boride networks along the grain boundaries, and its severity increases with carbon addition, especially for 2.5 wt pct of master alloy content. Sintering behavior, along with liquid generation, microstructural characteristics, and mechanical testing revealed that the reduced master alloy content from 2.5 to 1.5 wt pct (reaching overall boron content from 0.2 to 0.12 wt pct) was necessary for obtaining good ductility with better mechanical properties. Sintering with Ni-Mn-B master alloy enables the sintering activation by liquid phase formation in two stages to attain high density in PM steels suitable for high-performance applications.
Highlights
POWDER metallurgy (PM) steels for high-performance applications are of significant interest because of their low costs, flexibility in alloy design, and high volume production
This is due to the initial rearrangement of the powder particles from the prior master alloy melting (LP-1)
The liquid phase sintering of PM compacts with master alloy containing boron (Ni-Mn-B) added to water-atomized Fe and Fe-Mo-prealloyed base powders was investigated
Summary
POWDER metallurgy (PM) steels for high-performance applications are of significant interest because of their low costs, flexibility in alloy design, and high volume production. Reaching high density is not viable through conventional pressing and sintering which limits the usage of PM steel components in high-performance and demanding applications. Achieving high density is essential to obtain the demanding mechanical properties that will enable PM parts to serve as an alternative to conventionally manufactured parts. High densities can be achieved either through pressure-based or sintering-based techniques or by combining both.[1,2,3,4] Sintering with liquid phase forming additives activates the sintering and enhances the final.
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