Effect of Heat Treatment and Cold Rolling of Steel Sheet on Phosphate Coating

Abstract

This investigation has been carried out in order to show how heat treatments and cold rolling of steel sheets influence the phosphate coating and to make clear the relationship between the microstruc-ture of the steel and the phosphate nucleation.
The activity of phosphate reaction is determined by the number of phophate nuclei initially formed on the steel surface when commercial phosphate solutions are sprayed.
It is found that the activity of phosphate reaction is considerably affected by heat treatments andcold rolling of steel sheet; the phosphate nuclei increase with an increase of cold reduction and a raise of annealing temperature, decrease with an increase of the heating rate and a raise of the quenching temperature.
The consideration of the above results from the microstructural point of view leads to the conclusion that the preferred orientation of steel (mainly (111) texture paralleled to the rolling surface) has the greatest effect on the phosphate nucleation, and the cementite in the steel has the next on it, while the grain size (grain boundary) of the steel has little effect.
These conclusions are supported by experiment of the phosphate nucleation on single crystals of iron and large grains of steels.