1991 Volume 77 Issue 3 Pages 398-405
The effects of titanium and manganese contents on the surface state and the phosphatability of cold rolled steel sheets have been investigated with ESCA and SEM analyses.
The Mn-oxide and Ti-oxide are preferentially formed on the surface during annealing at 780°C in H2-N2 atmosphere. The surface concentration of Mn is three or four times as large as that of Ti on the 0.3 Mn-0.2 Ti added cold rolled steel sheet in this annealing condition.
The bulk Ti and the surface Mn-oxide affect the phosphatability whereas the surface Ti-oxide of a few at% does not interfere the phosphating reaction. The bulk Ti is electrochemically oxidized to Ti-oxide during phosphating. This reaction, which is accompanied by the evolution of hydrogen, suppresses the precipitation of phosphate crystalline. On the other hand, the surface Mn-oxide is able to dissolve in phosphate solution, and this dissolution increases the pH of the solution, resulting in the acceleration of the phosphate film formation.
