Abstract
A comparison was made between two experimental methods to determine the σ-phase volume fraction and three methods to model σ-phase growth in a niobium-stabilized stainless steel (AISI 347). The σ-phase volume fraction and precipitate size were determined in material statically aged and creep deformed at 700 °C with both KOH etched specimens using bright field optical microscopy (OM/BF) (conventional method) and specimens etched with oxalic acid using scanning electron microscopy and backscattered electrons (SEM/BSE) (new method). Both experimental methods used manual thresholding together with digital image analysis. The calculations were made with DICTRA software, using both the TCFE database and the SSOL database with some modification concerning the effect of silicon on the stability of σ-phase particles. The modeled σ-phase volume fractions showed rather good agreement with the measured results from statically aged materials using the new method. It was found that the stabilizing effect of silicon on σ phase should be included in the thermodynamic database used for modeling.
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