Comparison between Quantitative Metallography and Modeling of sigma-Phase Particle Growth in AISI 347 Stainless Steel

摘要

A comparison was made between two experimental methods to determine the sigma-phase volume fraction and three methods to model sigma -phase growth in a niobium-stabilized stainless steel (AISI347). The sigma -phase volume fraction and precipitate size were determined in material statically aged and creep deformed at 700 deg 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 sigma -phase particles. The modeled sigma -phase volume fractions showed rather good agreement with the measured results from statically aged material using the new method. It was found that the stabilizing effect of silicon on a phase should be included in the thermodynamic database used for modeling.