API 571 Certification (Corrosion & Materials) Practice Test

Which type of steel is most commonly affected by hydrogen embrittlement when cold worked?

1. 400 series stainless steel

2. Low alloy steel

3. Carbon steel

4. 300 series stainless steel

The correct answer is: Carbon steel

Hydrogen embrittlement is a process where the presence of hydrogen in metals leads to a significant loss of ductility, making them brittle and prone to cracking. Carbon steel is particularly susceptible to hydrogen embrittlement when it undergoes cold working. This is primarily due to its microstructural characteristics, which allow hydrogen to diffuse and gather in certain areas, creating conditions that can lead to cracking. When cold working processes are applied to carbon steel, dislocations in the microstructure are created, providing pathways for the hydrogen to enter and concentrate. This phenomenon is exacerbated when carbon steel is also subjected to other stressors, such as high-strength applications or exposure to acidic environments, making it an even more likely candidate for hydrogen embrittlement. In contrast, while other types of steel can experience hydrogen embrittlement, the risk is significantly lower compared to carbon steel, particularly due to differences in alloy composition and microstructure. For instance, 300 series stainless steel typically has a higher resistance to this form of embrittlement because of the presence of nickel and chromium which contributes to an overall more stable microstructure. Thus, carbon steel stands out as the steel type most commonly affected by hydrogen embrittlement when subjected to cold working.