Effect of NH4+ on the pitting corrosion behavior of 316 stainless steel in the chloride environment

•The effect of NH4+ on pitting growth of 316 stainless steel are clarified.•Pitting parameters are statistically analyzed in NH4+-containing environment.•The high applied potential can promote the rupture of the residual passive film.•NH4+ can promote the metastable pitting proliferation and transition process.•The pitting growth is controlled by diffusion.