Abstract
The effects of elements as Mn, S, and O in steel sheets on rusting tendency and the properties of the phosphate coatings formed thereon have been studied by using pure iron and low carbon rimmed steel sheets to which controlled amounts of these elements had been added.
The rate of rusing of base sheets is determined by the “pack rust test” and the humidity cabinet test, and the resistance to blistering of the laquered phosphated sheets is examined by the salt spray test.
The chemical reactivity of the steel surface is affected considerably by the presence of these elements; the rate of rusting increases substantially with increases of precipitated MnS and MnO, and the ability to form protective phosphate films increases with increase of total Mn content.
The above results can be ascribed to the property of MnS to accelerate iron dissolution anodically in both rusting and phosphating. While manganese in solid solution serves as a cathodic dipolarizer in phosphating. Manganese oxide has an effect since its precipitation during hot rolling changes the equilibrium of Mn and S in austenite and therefore favours precipitation of fine MnS during subsequent annealing.
