Phosphating method

In a continuous process of producing a phosphate coating on a ferrous metal substrate which comprises treating the ferrous metal substrate with an acidic solution of zinc phosphate in the presence of chlorate ions, and optionally nitrate ions, the improvement which consists in adding to the solution as coating proceeds a proportion of a rapid-acting secondary oxidant for ferrous ion which is sufficient to maintain the concentration of ferrous ion at less than 112 parts per million of the solution and which is selected from alkali metal nitrites, ammonium nitrite, hydrogen peroxide, compounds containing combined hydrogen peroxide which liberate hydrogen peroxide under acid conditions, sodium hypochlorite and peroxydiacid salts, there being present in the solution when in the steady state a proportion of the secondary oxidant of from 0 to 0.6 millimoles per liter of the solution.