Photoemission electron microscopy of growth of grain boundary ferrite allotriomorphs in chromium steel

Abstract

Structural and kinetic features of the growth of grain-boundary ferrite allotriomorphs in an Fe-0.2C-12Cr low-alloy steel have been examined continuously during their formation by photoemission electron microscopy. Observations on the morphological changes of the allotriomorphs during growth have been made, with particular attention given to the development of planar facets and large ledges or steps at the austenite/ferrite interfaces. Some comparisons are made with the microstructures observable by heat-treatment and examination using conventional methods. Data are presented on the growth rates of ferrite allotriomorphs with macroscopically convex but faceted interfaces, and with a macroscopically planar interface apparently migrating by a ledge mechanism. These experimental measurements are compared with theoretical values calculated for a plain-carbon steel.