Precipitation evolution in duplex stainless steel during isothermal aging at 700°C

Abstract

The precipitation evolution in UNS S82441 duplex stainless steel during isothermal aging at 700°C was investigated using scanning electron microscopy and transmission electron microscopy. The image analysis results revealed that nitrides, carbides and σ and χ phases nucleate simultaneously, and the growth of the intermetallic phases lags behind that of nitrides and carbides. Nitrides and carbides precipitated at the ferrite/ferrite interfaces are dissolved, and the χ phase transforms to the σ phase with prolonged aging. In the initial aging stages, the granular σ and χ phases grow and coalesce according to Ostwald ripening. With a treatment time exceeding 4 h, intermetallic grains having a size larger than those of the adjacent ferrite phase grow following a normal grain growth law, while those small in size keep ripening. The grain growth process of the intermetallic phases has been verified theoretically.