Which gas is associated with underbead cracking in welding?

• A. Argon
• B. Neon
• C. Oxygen
• D. Hydrogen

Answer: (D)

Underbead cracking happens when hydrogen embrittlement weakens the weld region and the surrounding heat-affected zone, so the gas involved is hydrogen. During welding, hydrogen can be picked up from moisture in flux, damp coatings, or contaminated filler metals. As the weld cools, hydrogen diffuses into the metal and promotes brittle cracking along the bead and near it. This is especially a risk for high-strength steels and certain welding processes where hydrogen content is higher. Proper drying of consumables, preheating to slow cooling, and post-weld heat treatment help minimize this problem. Inert shielding gases like argon protect the weld but don’t cause this cracking; neon isn’t commonly used in welding, and oxygen can cause oxidation and porosity but not hydrogen-induced underbead cracking.