Experimental and computational study on microstructural evolution in 2205 duplex stainless steel during high temperature aging

2205 duplex stainless steel (DSS) aged at temperatures between 700 °C and 1050 °C for different time intervals (5 min, 0.5 h, 1 h, 2 h) is studied. The evolution of secondary phases and the matrix with variation of aging time and temperature are measured by means of optical metallography (OM), SEM&EDS and BSE. The impact toughness, which reflects the effects of secondary phases, is also measured. It is shown that σ is the dominant secondary phase in the matrix. The σ phase precipitates at the austenite/ferrite boundaries or within ferritic grains, with the volume percent increasing with aging time and maximizing at 850 °C. Aided by Thermo-Calc software, the thermodynamic driving forces for χ phase and σ phase are calculated. Although the driving force for χ phase is larger than that for σ phase between 700 °C and 900 °C, σ phase appears before χ phase because of its rapid growth rate at higher aging temperatures. According to the OM analysis and thermodynamic calculations, 2205 DSS at aging temperatures above 1000 °C is composed of ferrite and austenite, its volume fraction of ferrite increases with the increase of aging temperature. Moreover, the kinetic calculation on the migration of austenite/ferrite interface after different aging time is present. The thermodynamic and kinetic calculation results on the microstructural evolution of 2205 DSS are in good agreement with the experimental results.