A TEM investigation of M23C6 carbide precipitation behaviour on varying grain boundary misorientations in 304 stainless steels

摘要: Transmission electron microscopy (TEM) along with electrochemical potentiokinetic reactivation (EPR) testing was performed on different grades of 304 stainless steel (0.01, 0.025, 0.05, and 0.07%C) in order to assess the sensitization precipitation behaviour grain boundary misorientations. The materials were heat treated at 670°C for 50 h subject regime. EPR data TEM observations revealed that when amount carbon increased degree density precipitates. Large angle misorientations (Θ>15°) prevalent all content {1 1 0} surface orientation found be major texturing orientation. steels lower contents nucleated a few small precipitates high boundaries, while larger amounts carbides observed boundaries higher contents. It deemed required energies nucleate grow A threshold (above 0.05% C) which fully saturate boundary. Precipitation followed types boundaries. highest energy (general random boundary) first, then non-coherent twin not coherent “critical nucleation energy”, γgb(crit.), therefore exist will occur This value range 16 mJ m-2<γgb(crit.)<265 m-2 corresponds special (coherent portions twins respectively) ageing temperature 670 °C. © 1998 Chapman & Hall