CORROSION RESEARCH ROUND‐UP

GERMANY Nitric acid corrosion of high‐alloy steels. Corrosion diagrams and iso‐corrosion lines of hardenable and non‐hardenable chromium steels, chrome‐nickel steels and some others containing other alloy constituents, in nitric acid solutions up to 67%, have been determined at all temperatures up to their boiling points under atmospheric pressure. The resistance to corrosion of the different types of steel under definite conditions can be derived from the curves constructed from the data obtained. Part of the corrosion data was used to study the effect of different alloy constituents by means of the graphic method. To achieve passivation the minimum content of chromium increases with rising concentration of acid and with increasing content of carbon in the alloy. Excessive additions of chromium have an inhibitive effect also. Manganese is very effective, especially in alloys containing up to 0.7%. Nickel, copper and silicon appreciably increase the risk of attack. Molybdenum has little or no effect except in the 67% boiling acid solutions, where corrosion is reduced as molybdenum content rises to 2%. With higher content the converse happens.