Effect of Cold Rolling on the Transformation Kinetics of Sigma- and Chi- Phases in UNS S32205 Duplex Stainless Steel

Duplex stainless steels have very good properties including good ductility, moderate toughness and good stress corrosion cracking resistance. These properties can be severely affected by the precipitation of sigma (σ) and chi (χ) phases, in particular ductility and toughness. The effect of cold deformation on the isothermal transformation kinetics of UNS S32205 steel was investigated. The steel was cold rolled up to 64 % reduction in thickness and annealed at 850 °C from 10 min up to 4320 min (3 days). Microstructural characterization used light optical and scanning electron microscopy, energy dispersive spectroscopy, and magnetic measurements. Formation of intermetallics is much faster in the cold-rolled samples. After 4320 min, samples show the same amounts of each phase for all rolling strains. Results have been validated by thermodynamic calculations.