Thermoanalytical sintering studies of Fe–C admixed with ferroboron performed in different atmospheres

Abstract

In the present research, Fe–0·8%C–0·88%B steel powder compacts were produced using ferroboron. Thermal analysis, i.e. dilatometry and differential thermal analysis/thermogravimetry, was performed in Ar and N₂ atmospheres, and the content of interstitial C, O and N was measured. In both atmospheres, boron activated the reduction of oxides above ∼665°C due to its high oxygen affinity. Mass gain in the range of 700–1200°C occurred in N₂ atmosphere but not in Ar; the former came along with the uptake of 0·18% nitrogen from the atmosphere. Differential thermal analysis graphs indicate the formation of binary Fe–B eutectic liquid phase in N₂ compared with ternary Fe–C–B liquid in Ar. It seems that the formation of boron nitride retards graphite dissolution in N₂. Energy dispersive spectrometry linescans confirm the formation of BN during sintering in nitrogen atmosphere, but the mechanism is not yet clear. In both atmospheres, the formation of liquid phase was accompanied by mass loss.

Keywords:

• Powder metallurgy
• Sintered steels
• Thermal analysis
• Ferroboron
• BN
• Liquid phase

The authors would like to thank Dr A. Limbeck and Mr C. A. Mukhtar for their support in performing the ICP–OES measurements.