Influence of ferrite-austenite distribution in 2205 duplex stainless steel on high-temperature solution nitriding behaviour

Duplex stainless steel 2205 was subjected to annealing treatments in the range of 1000-1200 degrees C to adjust the phase fractions of ferrite and austenite. Annealed steels were subsequently subjected to high-temperature so-lution nitriding, which transformed the surface-adjacent region into austenite under the influence of nitrogen ingress. Microstructural characterization of the pre-annealed state and the solution-nitrided cases were per-formed with X-ray diffractometry, light-optical microscopy, electron back-scatter diffraction and hardness indentation. The phase fractions of austenite and ferrite have a significant influence on the nitriding kinetics. A relatively high ferrite phase fraction results in finer grains in the nitrogen-stabilized austenite case. The devel-oping austenite case and the evolution of the microstructure during solution nitriding are discussed in a computational thermodynamics and kinetics context. Slower grain growth in the austenite cases for higher ferrite phase fractions can be understood in terms of phase distribution, alloying element partitioning, and possibly, pinning effect by M2N nitrides.

Automated summary

Duplex stainless steel 2205 was annealed to adjust the phase fractions, and then high-temperature solution nitriding was conducted. The influence of phase fractions on nitriding kinetics and the evolution of microstructure during solution nitriding were analyzed using various characterization techniques. It was found that higher ferrite phase fraction resulted in finer grains of nitrogen-stabilized austenite. The slower grain growth in higher ferrite phase fractions could be attributed to phase distribution, alloying element partitioning, and pinning effect by M2N nitrides.