Influence of Solution Treatment Temperature on Microstructural Properties of an Industrially Forged UNS S32750/1.4410/F53 Super Duplex Stainless Steel (SDSS) Alloy

In this present study, the influence of solution annealing temperature on microstructural properties of a forged Super Duplex Stainless Steel (SDSS) was investigated by SEM-BSE (Scanning Electron Microscopy-Backscattered Electrons) and SEM-EBSD (Scanning Electron Microscopy-Electron Backscatter Diffraction) techniques. A brief solution treatment was applied to the forged super duplex alloy, at different temperatures between 800 degrees C and 1100 degrees C, with a constant holding time of 0.6 ks (10 min). Microstructural characteristics such as nature, weight fraction, distribution and morphology of constituent phases, average grain-size and grain misorientation were analysed in relation to the solution annealing temperature. Experimental results have shown that the constituent phases in the SDSS alloy are delta-Fe, gamma-Fe and sigma (Cr-Fe) and that their properties are influenced by the solution treatment temperature. SEM examinations revealed microstructural modifications induced by the Cr rich precipitates along the delta/gamma and delta/delta grain boundaries, which may significantly affect the toughness and the corrosion resistance of the alloy. Solution annealing at 1100 degrees C led to complete dissolution of sigma (Cr-Fe) phase, the microstructure being formed of primary delta-Fe and gamma-Fe. The orientation relationship between delta/delta, gamma/gamma and delta/gamma grains was determined by electron back scattering diffraction (EBSD). Both primary constituent phase's microhardness and global microhardness were determined.