Sintering of Fe–C–BN steel compacts in different atmospheres studied by dilatometry and DTA/TG

Abstract

In the present work, 2%hBN was admixed with Fe–0·8C, and both dilatometric and differential thermal analysis/thermogravimetry investigations were conducted in Ar and N₂ atmospheres, followed by microstructural studies and mechanical testing. The α–γ phase transformation in both atmospheres was found to occur in the temperature range of plain iron and not, as expected, in that common for Fe–C. In the Ar atmosphere, liquid phase formation is recognised by endothermic differential thermal analysis signal and shrinkage in the dilatometer during the heating stage at ∼1275°C. In contrast to the activating effect of the inert Ar for the decomposition of hBN, the deactivating effect of the N₂ atmosphere is visible from the dilatometry results: sintering in N₂ even resulted in slight expansion during the isothermal stage. Therefore, the, at first surprising, conclusion can be drawn that the chemically inert Ar is activating the sintering process while the more reactive N₂ passivates it.

Keywords:

• Sintered steels
• Boron
• Sintering atmosphere
• Thermal analysis
• Liquid phase