At temperatures over 70°C, is hydrogen-induced cracking (HIC) more likely or less likely?

Hydrogen-induced cracking (HIC) is a type of failure that occurs in metals, particularly steels, when they are exposed to hydrogen under certain conditions. At elevated temperatures, such as those over 70°C, the solubility of hydrogen in steel increases, which generally allows for easier diffusion of hydrogen into the metal. However, this increased temperature can also facilitate the thermal expulsion of hydrogen from the metal matrix, reducing the concentration of dissolved hydrogen.

As the temperature rises, the mobility of dislocations within the crystal structure of the metal enhances, allowing for more energy to alleviate stresses that can lead to cracking. Therefore, while the presence of hydrogen may still pose a risk, the overall activity at elevated temperatures tends to reduce the likelihood of HIC occurring. The combination of increased solubility and diffusion rates, along with the modifications in mechanical properties of the steel at higher temperatures, leads to a general trend of reduced risk of HIC in comparison to lower temperatures.

Consequently, stating that hydrogen-induced cracking is less likely at temperatures over 70°C aligns with the fundamental principles of material science and corrosion engineering.