Grain and grain boundary characters in surface layer of untreated and plasma nitrocarburized 18Ni maraging steel with nanocrystalline structure

► Sizes of γ′-Fe4N and α-Fe grains in the surface layer of the steel are nanoscale. ► Number fractions of CSL and low angle boundaries for α-Fe grains reduce. ► γ′-Fe4N grain boundaries are made up of high angle, low angle and CSL boundaries.