Controlling the amount of chromium to be on tin and iron substrates is important for the production of special steel sheet for welded can material, partially tin precoated and then fully coated with chromium. The deposition behaviour of chromium on tin and iron substrates was studied by means of the polarization behaviour of tin and iron in a chromium coating bath. For stable deposition, a higher current density is required on tin than on iron due to the higher hydrogen over-voltage on tin. Ageing in air after tin coating and preliminary electrolysis under the potential range of reduction of Cr6+ to Cr0 in a chromium coating bath are effective in facilitating the formation of a cathode film and encouraging the deposition. A study on a continuous coating line showed that the amount of chromium to be deposited on tin and iron can be industrially controlled by a process involving a lower current density in the first step and a higher current density in the second.