51314-4321-Stress Corrosion Cracking of Cold Drawn Ferrito-Pearlitic Steels in Confined Aqueous Solutions Containing Dissolved CO2

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Product Number: 51314-4321-SG

ISBN: 4321 2014 CP

Author: Alix Vancostenoble

Publication Date: 2014

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Corrosion of carbon steels in aqueous solution is well known to increase with the content of dissolved CO2 and depends directly on the pH of the environment depending on the CO2 partial pressure. In confined environments when the ratio of solution volume to steel surface is very low it has been shown that the corrosion rate is significantly reduced down to some micrometers per year. In such environments supersaturation of the solution with iron cations leads to increase the pH and favors the formation of a carbonate iron scale FeCO3 acting as a protective layer. Thereby environment fluctuations (such as pH potential …) and/or the addition of applied stress may disturb the equilibrium between the steel and its protective layer causing the initiation and propagation of a stress corrosion cracking (SCC) phenomenon.In this study the effects of these variables on the initiation and propagation of cracks in two cold drawn ferrito-pearlitic high strength steels are investigated. Their microstructure is characterized for one by a ferrite and a fine lamellar pearlite and for the other by a ferrite and spheroidized pearlite due to a subsequent thermal treatment. Each one conserves a strong microstructural and crystallographic anisotropy. Slow strain rate tensile tests were conducted on smooth and micro-notched specimen in aqueous chloride solution saturated in CO2 at pH 5.5 to 6. Open circuit potential (OCP) and cathodic protection (CP) conditions were explored. Under OCP conditions slow strain rate tensile tests were performed in a confined environment. The results indicate a strong resistance to SCC for the two steels. High plastic deformation should be applied before producing embrittlement and highlighting an environment assisted cracking on smooth specimens. The anodic dissolution rate plays a key role in the formation of critical defects causing crack initiation. Hydorgen interacts with the local plasticity at the µ-notch/crack tip and causes delamination at pearlite/ferrite interfaces.