Characterization of hydrogen embrittlement in high-strength fastener steels: mechanical testing and numerical modeling

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High strength and ultrahigh strength mechanical fasteners are broadly characterized by tensile strengths ranging from 1,000 to 2,000 MPa, and are often used in critical applications. Damage resulting from hydrogen embrittlement can occur by a complex interaction of material characteristics, environmental conditions, manufacturing flaws, installation conditions, and joint design criteria. The consequences of failures can range from minimal to catastrophic, even resulting in loss of life. Hydrogen embrittlement (HE) is a common problem in high strength steel caused by the absorption of elemental hydrogen into the material matrix. Hydrogen damage in high strength steel fasteners can be summarized as a migration of mobile hydrogen from lattice sites to points of stress concentration, resulting in crack initiation followed by crack propagation by atomic bond decohesion at the crack tip. The effect of hydrogen embrittlement in materials is generally characterized by various types of slow strain rate tests and incremental step load tests which quantify the loss of mechanical properties such as strength and ductility.