Stress Corrosion Cracking and Hydrogen Embrittlement Atmospheric Corrosion Testing of Control and Prototype Steels

Abstract

The United States Department of Defense has begun the formulation of a new generation of high strength steels for naval applications, emphasizing superior hardness, toughness, and ballistic resistance. Whilst these metals have been designed with a focus on strength, their corrosion behavior is largely unknown and must be characterized prior to widespread application. This research involved the design of an experiment to test the stress corrosion cracking and hydrogen embrittlement susceptibility of HY-100, HSLA-150, 10Ni QQT, and 10 Ni QQLT steels. A modified version of the standardized four-point bend test in which samples are stressed to 90% of their yield strength was designed to be implemented in numerous microclimates across the State of Hawai’i. In addition, microstructural analysis was performed via metallurgical techniques, while the corrosion behavior was quantified via electrochemical polarization. Inclusions were characterized in each steel, with directional, structural, and elemental analyses performed. Aluminum and iron containing oxides were identified in each metal, with 10Ni steels showing the highest frequency of inclusion clusters. Potentiodynamic polarization testing provided information pertaining to the corrosion rates of each steel along with zinc and magnesium in three solutions simulating freshwater, acidic, and saline environments. While all four steels produced similar galvanic potential and current density results, magnesium was shown to induce the highest levels of hydrogen liberation on the steels with rates consistently two orders of magnitude greater than that due to zinc. Combined, the information obtained as related to stress corrosion cracking, hydrogen embrittlement, and material characterization serve as integral pieces necessary to validate and further refine the next generation of high strength steels for defense applications.