THE DETERMINATION OF HYDROGEN EMBRITTLEMENT BEHAVIOR OF ARMOR STEELS BY EXPERIMENTAL METHODS AND THE OPTIMIZATION OF HYDROGEN BACK-DIFFUSION OPERATION

Abstract

Hydrogen embrittlement, also known as hydrogen attack or hydrogen-assisted cracking, is a process whereby metallic materials (i.e., high-strength steels, titanium alloys and aluminum alloys) become brittle or fractures due to the exposure, introduction and diffusion of hydrogen atoms through the microstructure of metals. It is a serious matter that drastically degrades the mechanical properties (e.g., ductility and toughness) of a wide range of different structural materials which include pipeline steels, armor steels, advanced high strength steels, etc. This thesis study aims to investigate the hydrogen embrittlement behavior of armor steels that conform to MIL-DTL-12560 Class 4a and MIL-DTL-46100 military specifications used by FNSS Defense Systems Inc. and to optimize the temperature and duration parameters of hydrogen back-diffusion operation to reduce the risk of hydrogen embrittlement. To characterize the embrittlement behavior of armor steels used by FNSS, various mechanical tests, including tensile tests, compression tests, high strain rate tests, hardness tests, CVN impact tests and ballistic tests, were carried out with as-received and hydrogen-uncharged specimens in order to unveil the adverse effects of hydrogen embrittlement on the mechanical properties of these steels. A cathodic hydrogen charging system was used to charge the specimens with hydrogen for mechanical tests. The effects of microstructure on the mechanical response of materials were also investigated for deeper understanding.