Potential-Time Curves obtained during the Stress Cracking of Metals

Abstract

WE have investigated some of the electrochemistry of two 12 per cent chromium martensitic steels while undergoing cracking in acid media. Since it is known that these steels can be made to crack through hydrogen embrittlement as well as by stress corrosion, we were curious as to the cause of cracking in 1 per cent hydrochloric acid with 1 per cent dissolved selenium dioxide. Following the procedure of Brown¹, increasingly larger polarizing currents, both anodic and cathodic, were applied to stressed beam specimens to determine which reaction hastened the time to failure. From these results we concluded that the cracking in this medium was by hydrogen embrittlement. Further proof was obtained by substituting sulphuric acid for hydrochloric acid (to eliminate the possible stress corroding influence of the chloride ion) without any change in the pattern of results. Simultaneously with our tests on the effect of applied currents on time to fracture, potential-time curves were automatically recorded. The rather unusual changes in potential we observed are primarily the reason for this communication.