A nanocrystalline layer was fabricated in bond area of 0Cr16Ni22Mo2Ti steel using flash welding. The average grain size near bond line is about 30 nm and the farther the distance from the bond line, the larger the size of the nanocrystallites. The thickness of the nanocrystalline layer is about 80 \\micron. The formation mechanism of the nanocrystallites may be that the metal in liquid state in the bond area is solidified under both high undercooling and high density d.c. electric current that can refine the microstructure of metal solidification.