EFFECT OF SCALING ON THE CORROSION RESISTANCE OF CAST STEELS

Abstract

Resistance to the corrosion by sea water was experimented with specimens of cast steel with scales and shaper-finished specimens without scales. As for painted specimens, three kinds such as the blank, specimens those coated with the ship's bottom paint and those coated with zinc were experimented. The comparative experiments covered the change of weight, the solution potential and the tensile properties after corrosion. The result of the experiments was summarised as follows:
(1) In case the immersion time is short, the corrosion resistance of specimens with scales is higher than the shaper-finished ones without scales. However, as the time of immersion increases, the corrosion develops and scales peel off, when the weight abruptly decreases and the attack is more remarkable than in the finished specimens.
(2) The scales are electrochemically positive against the finished specimens and favors the corrosion resistance. However, with the increase of the immersion time the difference of the solution potential becomes less and the effect of aforementioned factor prevails.
(3) In either case, the zinc-coating is effective, but the ship's_bottom paint is the best coating.
(4) Considering from the results of the tensile test, no brittleness due to corrosion is observed in such degree of corrosion.