The purpose of this paper is to study the effect of high nitrogen content on corrosion behavior of austenitic stainless steels in seawater under severe conditions such as tensile stresses and existence of sensitization in the structure. A constant tensile stress has been applied to sensitized specimens types 304, 316L, 304LN, 304NH, and 316NH stainless steels. Microstructure investigation revealed various degrees of stress corrosion cracking. SCC was severe in type 304, moderate in types 316L and 304LN, and very slight in types 304NH and 316NH. The electrochemical polarization curves showed an obvious second current peak for the sensitized alloys which indicated the existence of second phase in the structure and the presence of intergranular stress corrosion cracking. EPR test provided a rapid and efficient nondestructive testing method for showing passivity, degree of sensitization and determining IGSCC for stainless steels in seawater. A significant conclusion was obtained that austenitic stainless steels of high nitrogen content corrode at a much slower rate increase pitting resistance and offer an excellent resistance to stress corrosion cracking in seawater. 1. Introduction Austenitic stainless steels have been used successfully in many applications in marine environment. Types 304 and 316L are the most likely candidates for marine applications due to their excellent corrosion resistance especially for pitting and crevice. Therefore, they are found in excess in work-boat propellers, pump components, valves, shaft components, hull fittings, fasteners, and oceanographic instruments [1]. Type 316L stainless steels are considered to be the main components in hydraulic control systems for the operation of subsea oil recovery system. These alloys also are used in instrument and chemical injection tubing in offshore oil platform [2–4]. In many marine applications, the corrosion resistance of the traditional types 304/316L stainless steels may not be sufficient, particularly for more demanding applications such as continuous immersion or exposure at elevated temperatures. It has been shown by the Welding Research Council [5] that 300 series stainless steels, heavily sensitized by furnace heat treatment, displayed intergranular corrosion in ambient seawater exposures. Austenitic stainless steels are generally susceptible to stress corrosion cracking (SCC) in chloride containing environments at high temperature. This type of cracking, defined as chloride stress corrosion cracking (CSCC), is mostly transgranular in nature and is not affected by the change in
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