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.

Research highlights▶ σ is the first phase to appear at higher temperature because of rapid growth rate. ▶ Thermodynamic driving force for χ phase is always larger than that for σ phase. ▶ The kinetic calculation on the migration of γ/α interface during aging is present.