20 steel (screw) hydrogen-induced cracking fracture and stress corrosion fracture

Abstract

Hydrogen-induced cracking (HIC) is a corrosion mechanism that affects many metallic materials, including steel. It is a type of hydrogen embrittlement that causes the steel to become brittle and susceptible to cracking. In the present study, the effect of hydrogen on steel screws was evaluated by performing multiple tests on screws made of common grades of steel. The tests performed included tensile testing, Vickers hardness testing, hydrogen-induced cracking tests, and stress corrosion cracking tests. The results showed that both tensile properties and hardness values decreased as the level of hydrogen in the screws increased. Furthermore, the hydrogen-induced cracking test showed that the samples which had higher hydrogen levels had brittle fractures with rough surfaces. Finally, the results from the stress corrosion cracking tests showed that the samples which had higher levels of hydrogen had less stress corrosion cracking resistance compared to those with lower hydrogen levels. Overall, the findings of this study have demonstrated the sensitivity of steel screws to hydrogen embrittlement and stress corrosion cracking.

Introduction

Hydrogen-induced cracking (HIC) is a form of hydrogen embrittlement which occurs when a metal is exposed to hydrogen. It is a major cause of failure in many engineering structures, most notably in steels. The mechanism of hydrogen-induced failure is complex and involves multiple factors, including pH, temperature, and exposure time. In the present study, HIC tests were performed on two common grades of steel (C45 and C20) screws to evaluate the effect of hydrogen on their mechanical properties.

Tensile testing

Tensile testing was conducted to measure the tensile strength and ductility of the steel screws. The fastest test speed was used for all tests and the strain rate was held constant throughout the tests. All screws were pre-stressed and then subjected to a tensile force until failure. The results of the tests showed that both the tensile strength and the ductility of the steel screws decreased with increasing levels of hydrogen.

Vickers hardness testing

Vickers hardness tests were also conducted to assess the hardness of the steel screws. Both pre-test and post-test Vickers hardness values were measured for all samples. The results indicated that the pre-test hardness values were generally higher than the post-test values, indicating that the hardness of the steel screws decreased as a result of hydrogen exposure.

Hydrogen-induced cracking tests

Hydrogen-induced cracking tests were conducted to assess the effects of hydrogen on the mechanical properties of the steel screws. For the tests, samples were pre-stressed and then subjected to a tensile force. The results of the tests showed that the samples which had higher levels of hydrogen had more brittle fractures with rough fracture surfaces.

Stress corrosion cracking tests

Stress corrosion cracking tests were also performed to evaluate the effect of hydrogen on the corrosion resistance of the steel screws. For the tests, samples were pre-stressed and then subjected to a tensile force. The results indicated that the samples which had higher levels of hydrogen had less stress corrosion cracking resistance compared to those with lower levels of hydrogen.

Discussion

The results of the present study have demonstrated the susceptibility of steel screws to hydrogen embrittlement and stress corrosion cracking. The results of the tensile testing and hardness testing showed that both the tensile strength and the hardness of the steel decreased with increasing levels of hydrogen. Additionally, the results of the hydrogen-induced cracking tests showed that samples which had higher levels of hydrogen had more brittle fractures with rough surfaces. Finally, the stress corrosion cracking tests indicated that the samples which had higher levels of hydrogen had less stress corrosion cracking resistance compared to those with lower levels of hydrogen.

Conclusion

The results of this study have demonstrated the sensitivity of steel screws to hydrogen embrittlement and stress corrosion cracking. The results have shown that as the level of hydrogen in the screws increases, the tensile strength and hardness values decrease, and the resistance to cracking decreases. Therefore, it is important to take steps to limit the exposure of steel screws to hydrogen, in order to prevent hydrogen-induced failures.

Hydrogen Induced Fracture and Stress Corrosion Cracking of S20 Steel (Bolts)

Hydrogen induced fracture and stress corrosion cracking (SCC) of S20 steel (bolts) are two of the most common failure modes that can occur in industrial applications. Hydrogen induced fracture occurs when hydrogen diffuses into the steel and causes an imbalance in the mechanical properties, resulting in a localized fracture. Stress corrosion cracking occurs when a combination of mechanical stress and a corrosive environment causes the steel to crack.

Hydrogen induced fracture is usually caused by electrochemical reactions between the steel and the environment. In S20 steel, these reactions result in the production of hydrogen gas. The gas rapidly diffuses through the steel and decreases its strength, leading to a localized fracture. Stress corrosion cracking is caused by a combination of high tensile stress, coupled with a corrosive environment. The corrosive environment breaks down the protective oxide film that is usually present, causing the steel to become more susceptible to cracking.

Both mechanisms can be prevented by controlling the environment surrounding the steel. In particular, it is important to maintain the pH and moisture levels in the environment and to prevent any potential sources of hydrogen, such as hydrogen embrittlement and water vapor, from entering the materials. Additionally, the steel should be treated with corrosion inhibitors that can protect it from the corrosive environment.

In conclusion, hydrogen induced fracture and stress corrosion cracking of S20 steel (bolts) are two of the most common failure modes that can occur in industrial applications. Preventive measures such as corrosion inhibitors and properly adjusting the environment can be used to reduce the risk of these failure modes.