Hot cracking is best described as.

• A. Cracking occurs after the weld has cooled in service.
• B. Cracking during solidification caused by hydrogen and residual stresses, especially in hardenable alloys.
• C. Cracking due to corrosion at the weld.
• D. Cracking caused by improper filler spacing.

Answer: (B)

Hot cracking occurs while the weld metal is still molten or semi-solid as it solidifies. It happens when hydrogen present in the weld and the residual stresses from restraint create weaknesses at the grain boundaries as the material around the weld solidifies, leading to cracks that form during solidification. This is especially likely in hardenable alloys that have a wide solidification temperature range and limited ductility in the solid state. In short, the crack develops during solidification due to hydrogen and thermal/constraint stresses, rather than forming after cooling or from environmental corrosion or filler spacing issues.