What does hydrogen embrittlement cause?

• A. Hydrogen embrittlement causes surface rust.
• B. It strengthens bonds preventing cracking.
• C. It reduces corrosion by passivation.
• D. Hydrogen embrittlement causes micro-cracks and macroscopic cracking to rupture the metal.

Answer: (D)

Hydrogen embrittlement happens when hydrogen atoms diffuse into a metal and weaken its ability to deform plastically, especially under tensile stress. These hydrogen atoms tend to collect at microstructural features like grain boundaries and dislocations, reducing cohesive strength and promoting crack initiation. Under loading, the existing microcracks can grow and link up, producing macroscopic cracks that lead to rupture of the metal. This is why the statement about micro-cracks and macroscopic cracking causing rupture is the accurate description. The other options describe surface rust, strengthening, or enhanced passivation, which are not effects of hydrogen embrittlement.