INFLUENCE OF SOLUTION TREATMENT TEMPERATURE ON MICROSTRUCTURAL AND MECHANICAL PROPERTIES OF HOT ROLLED UNS S32760 / F55 SUPER DUPLEX STAINLESS STEEL (SDSS)

The effects of solution treatment temperature on the microstructural evolution and mechanical properties of hot rolled F55 super duplex stainless steel has been studied in this paper. The F55 alloy was hot deformed at 1000 degrees C, with 60% total deformation degree in 5 rolling steps, and heat treated by solution treating at 1000 degrees C, 1050 degrees C and 1100 degrees C for 20 Minutes. The samples microstructure was investigated by Scanning Electron Microscopy-Electron Backscatter Diffraction (SEM-EBSD) techniques. Microstructural characteristics such as weight fraction, distribution and morphology of constituent phases and grain misorientation were analyzed in relation to thermomechanical processing conditions. All samples were tensile tested to quantify the effect of thermomechanical processing on mechanical properties (ultimate tensile strength, yield strength and elongation to fracture). Experimental results showed that the constituent phases in the SDSS alloy can be ferrite phase (delta), austenite phase (gamma) and sigma phase (sigma), depending on applied solution treatment. Obtained microstructure after hot deformation and solution treatment at 1000 degrees C showed a mixture of ferrite, austenite, and sigma phases. In the case of solution treatments at temperatures above 1050 degrees C the deleterious sigma phase is no longer observed. Investigations on mechanical properties showed that increasing solution treatment temperature, increases elongation to fracture, while strength properties are decreased, all due to the presence / absence of deleterious sigma phase.