TEM investigation of high-nitrogen chromium steels for power plant applications

High-nitrogen chromium steels for power plant application were investigated. The mechanical properties of these steels are determined by microstructural parameters such as volume fraction and dispersion of precipitates, grain size and dislocation density. The proper ausaging treatment followed by controlled cooling is an effective tool to control the particle/dislocation substructure. The modification of microstructure of the high-nitrogen chromium steels is achieved by the control of dissolution and reprecipitation of MN-type vanadium nitrides with a face-centered cubic crystal structure. Tempering after ausaging results in softening associated with pronounced recovery of dislocation structure and precipitation of carbonitrides.