Thermodynamic Calculations for the Investigation of Phase Formation in Boron-Modified Ferritic Stainless Steel

Abstract

Thermodynamic calculations in equilibrium condition were used to investigate the phase formation sequence and microstructure formation in a boron-modified ferritic stainless steel. The results were also compared with spray forming experimental heats. The thermodynamic calculations indicated that there is an eutectic point at around 1.1 wt.% B and therefore two different compositions (hypo and hypereutectic) were experimentally investigated. For the hypoeutectic composition, the primary phase to form from the melt was δ-ferrite with the boride phase M2B originating eutectically. Conversely, for the hypereutectic composition, the boride M2B was formed as the primary phase. The prediction of phase formation and stable phases at room temperature was accurate. The calculated melting temperatures showed considerable deviation from values measured by Differential Scanning Calorimetry. The final spray formed microstructure and the phase fractions were to some extent in accordance with the thermodynamic calculations.