Alloy and composition dependence of hydrogen embrittlement susceptibility in high-strength steel fasteners

Abstract

High-strength steel fasteners characterized by tensile strengths above 1100 MPa are often used in critical applications where a failure can have catastrophic consequences. Preventing hydrogen embrittlement (HE) failure is a fundamental concern implicating the entire fastener supply chain. Research is typically conducted under idealized conditions that cannot be translated into know-how prescribed in fastener industry standards and practices. Additionally, inconsistencies and even contradictions in fastener industry standards have led to much confusion and many preventable or misdiagnosed fastener failures. HE susceptibility is a function of the material condition, which is comprehensively described by the metallurgical and mechanical properties. Material strength has a first-order effect on HE susceptibility, which increases significantly above 1200 MPa and is characterized by a ductile--brittle transition. For a given concentration of hydrogen and at equal strength, the critical strength above which the ductile-brittle transition begins can vary due to second-order effects of chemistry, tempering temperature and sub-microstructure. Additionally, non-homogeneity of the metallurgical structure resulting from poorly controlled heat treatment, impurities and non-metallic inclusions can increase HE susceptibility of steel in ways that are measurable but unpredictable. Below 1200 MPa, non-conforming quality is often the root cause of real-life failures.This article is part of the themed issue 'The challenges of hydrogen and metals'.

Evaluation of Steels Susceptibility to Hydrogen Embrittlement: A Thermal Desorption Spectroscopy-Based Approach Coupled with Artificial Neural Network

“…Susceptibility of steels to HE increases with an increase in material strength. This relationship was extensively studied evidencing that material conditions such as strength and/or hardness are primary conditions defining the susceptibility of steels to HE [11][12][13]. The results, as presented in Figure 4, confirm the statement showing a certain tendency between UTS, YS, and HSP of the studied steel grades.…”

“…The linear regression modeling reveals a comparable HSP prediction quality at YS and UTS data for the studied steels, caused apparently by its high cross correlation rate, as shown in Figure 5. Brahimi et al [11] showed the embrittlement ratio decreasing smoothly with an increase in the hardness of individual high-strength steel grades. However, different alloys can have different hydrogen sensitivities despite the similar properties of hardness/strength that complicate the accurate prediction of changes in the steel properties in the presence of hydrogen [11,13].…”

“…Another way to evaluate the macroscopic mechanical response (namely, ultimate tensile strength, yield stress, and elongation to fracture) was proposed by Thankachan et al for aluminum alloys using artificial neural network (ANN), creating a strong relationship between the input data (chemical composition, strain rate, and hydrogen charging conditions) and the targeted performance parameters of mechanical response. In addition, a strong correlation between steel hardness/strength and HE susceptibility was defined for individual steels after different heat treatment procedures [11][12][13]. The second-order effect on HE susceptibility was attributed to several factors, including chemical composition and heat treatment, that control the microstructure of the materials.…”

“…The second-order effect on HE susceptibility was attributed to several factors, including chemical composition and heat treatment, that control the microstructure of the materials. These factors ultimately affect hydrogen diffusion and trapping [11]. Nevertheless, systematic research of hydrogen-metal interactions in different alloys is important for the development of a robust modeling approach for in-situ assessment and prediction of HE in actual engineering applications [3,13,14].…”

Hydrogen induced fast-fracture

“…Effect of yield strength Among the parameters that determine the susceptibility to hydrogen embrittlement, the yield strength has been identified as having a significant effect with high strength metals most susceptible irrespective of composition or structure. For example, data presented by Brahimi et al (2017) suggests that for a given set of hydrogen charging conditions, the HEE index reduces from 0.5 for a steel with a Rockwell hardness 40 HRC to a HEE of less than 0.25 for a 52 HRC steel. We now investigate the effect of the yield strength on the tensile fracture strength using the model developed here.…”