Hydrogen-induced cracking is most likely to occur under which conditions?

• A. Low hydrogen welding and mild steel.
• B. High-strength or hardenable steels with high hydrogen content welds and high hardness in the heat-affected zone.
• C. Welding nonferrous metals.
• D. In dry environments only.

Answer: (B)

Hydrogen-induced cracking happens when hydrogen enters the weld region and diffuses into the metal, concentrating at defects and grain boundaries under tensile stresses. This is especially dangerous when the steel in the weld zone is very hard, because hard microstructures are more brittle and easier for hydrogen to exploit to start and propagate cracks.

The scenario described—high-strength or hardenable steels with welds that have a high hydrogen content and a heat-affected zone that is very hard—poses the greatest risk. High-strength or hardenable steels can form a martensitic or otherwise very hard HAZ during welding; hydrogen in the weld or surrounding environment can then interact with that hard, brittle matrix, promoting cracking along the HAZ or within the weld metal.

Other options don’t fit as well because HIC is driven by the combination of susceptible steel microstructure (high hardness in the HAZ) and hydrogen presence, not by the environment being dry alone or by welding nonferrous metals. Mild steels with low hydrogen content and a dry environment reduce risk, and nonferrous metals behave differently with respect to hydrogen embrittlement.