An uniform nitrogen content in the surface and interior was
obtained by solution annealing some steels in an atmosphere
blowing 0.3 l/min argon gas at 1100 ◦C for 2 h after the HTGN
heat treatment for 10 h (HTGN-SA). Subsequently,
Optical microscopy (OM), scanning
electron microscopy (SEM-EDS) technique (JSM-6700f,
Japan)