Influence of the quenching rate on the spinodal decomposition in a duplex stainless steel

Cast duplex stainless steels are known to be susceptible to embrittlement after long term ageing at intermediate temperatures (300-400°C). This embrittlement is related to the spinodal decomposition that occurs in the ferrite phase. Steels of equivalent composition after undergoing the seemingly same heat treatment exhibit different microstructural and mechanical evolutions. One of the assumptions which explains this is based on the influence of the quenching rate. For this purpose, a set of different cooling rates (2°C/s to 20°C/s) has been applied, and the resulting microstucture analysed. The atom probe was used because of its capability to investigate the finescale α-α' spinodal decomposition of the ferrite. It is shown that the quenching rate influences both the initial composition amplitude in unaged specimens and the rate of development of chromium concentration fluctuations in the aged ferrite.