Study on Precipitation in Austenitic Stainless Steel 18Cr18Mn2MoN During Isothermal Aging at 900

The precipitation of nitrides(carbides) in solution treatment and aging process of 18Cr18Mn2MoN high nitrogen austenitic stainless steel was investigated by use of metallographic and electron microscopical analysis.The results show that precipitation process of Cr2N is divided in three steps:first,precipitation of chain-like Cr2N along grain boundaries;Second,precipitation of cellular Cr2N at meeting point of three intergranulars and a small amount of Cr2N precipitated in transgranularly;third,Cr2N precipitates grow from grain boundaries into grain gradually and are connected with trans granular Cr2N forming tablets and cover whole grain.with nitrides precipitation,σ,χ and γ′ phases are formed.The precipitation mechanism is discussed.The crystalline structure of precipitates and orientation relationship between precipitates and matrix were studied with transmission electron microscopy(TEM) and selected area electron diffraction(SAD).