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R. Oro Calderon, C. Gierl-Mayer, H. Danninger:
"Application of thermal analysis techniques to study the oxidation/ reduction phenomena during sintering of steels containing oxygensensitive alloying elements";
Journal of Thermal Analysis and Calorimetry, 127 (2017), 1; S. 91 - 105.

For the consolidation of steel parts manufactured
by powder metallurgy (PM) techniques, removal of the
surface oxides covering metallic powder particles is a
necessary prerequisite. In PM steels with conventional
compositions, reduction of the oxides is easily achieved in
traditional sintering furnaces. However, processing steels
containing alloying elements with a high oxygen affinity
represents a big challenge that requires a deeper understanding
of the chemical processes occurring during sintering.
In the present work, thermogravimetry analysis
coupled with mass spectrometry is used to describe the
oxidation/reduction phenomena that take place when sintering
steel powders and how these processes are modified
by the addition of admixed particles containing oxygensensitive
elements. Carbothermal reduction processes are
studied using pure oxides (Fe2O3, MnO2, Cr2O3 and SiO2)
as well as water-atomized Fe powders mixed with small
amounts-4 mass/%-of Cr, Mn and Si powders or Fe-
Mn-Si-(Cr) master alloy powders. The results show that
there is an oxygen transfer from the base iron particles to
the oxidation-sensitive elements-``internal getter
effect´´-taking place mostly through the gas phase. Different
alloying elements (Cr, Mn, Si) show different temperature
ranges of susceptibility to oxidation. Combination
of these oxygen-sensitive alloying elements in the form of
a master alloy powder reduces their sensitivity to oxidation.
Also, the use of master alloys promotes the concentration
of the oxides on the surface of the alloying particles and not
in the grain boundaries of the surrounding iron particles-
as occurs when using Mn carriers-which should have a
beneficial impact on the final mechanical performance.

Oxidation/reduction phenomena Carbothermal reduction Sintered steels Oxygen-sensitive alloying elements Master alloys Fe-Mn-Si-Cr steels

http://dx.doi.org/10.1007/s10973-016-5508-5