Abstract
The formation of surface alloy layers through the diffusion annealing of nickel-plated stainless steels was performed. The diffusion annealing was applied in a temperature range from 1173 to 1373 K for 180-600 s in Ar atmosphere to nickel-plated SUS430 and 304 stainless steels. The thickness of the alloy layer, diffusion velocities and distribution of Ni and Cr in the surface layer were estimated from EPMA line analysis. Corrosion tests of the surface alloyed stainless steels were carried out by immersion in 10%H2SO4 solution at 323 K for max. 28.8 ks, exposure to a gas mixture of air containing 20 ppm SO2 at 308 K for 28.8 ks, and cyclic dip in 5%NaCl at 323 K for 1.8 ks and dry in air at 343 K for 1.8 ks.
The results obtained are as follows: (1) The surface alloy layer is rapidly formed by annealing for 300 s above 1173 K, and no nickel layer remains after annealing at 1273 K for 300 s. (2) The thicker the nickel plating and the higher the annealing temperature, the higher is the diffusion velocity. (3) After annealing treatment of the nickel-plated SUS430 and 304, the surface alloy layers are composed of 20 mass%Ni and 13 mass%Cr, and 35 mass%Ni and 15 mass%Cr, respectively. (4) The surface alloyed SUS430 and 304 stainless steels possess higher corrosion resistance than the unalloyed counterparts.
