Hot cracks are a metallurgical defect that occurs during the final phase of solidification when a metal is exposed to high thermal tensile stresses. Hot cracks are normally seen in welded joints when cracks propagate intergranular (along the grain boundaries) and are caused by weak cohesion of a metal in a semi-molten state.

Key Features:

• Locations of Hot Cracks: Hot cracks are generally located in the weld metal and heat-affected zone (HAZ) areas and generally appear in alloys such as stainless steel and aluminum.
• Cause of Hot Cracks: Hot cracks are promoted by the presence of low melting point elements such as sulfur, phosphorus, and carbon which increases cracking susceptibility as the metal goes through the cooling stage.
• Condition for Hot Cracks: Hot cracks usually can occur when rapid cooling, excessive heat input or restrained joints combine together to produce thermal stresses thus creating a condition for hot cracks to form.

Hot cracks are considered a critical defect that compromises structural integrity and safety in many industries such as aerospace, automotive, shipbuilding, and pressure vessels. Hot cracks are often not detected by visual inspection and many non-destructive testing methods such as ultrasonic or x-ray are sometimes required to detect hot cracks. Not detecting hot cracks could result in significant failures during the operational periods of components such as leaking, deformation, or fracturing of the component when subjected to operational force or stress. Some ways to potentially minimize the risk of hot cracks could consist of controlling welding procedure and parameters, using low-susceptibility alloys, preheating, and post-weld heat treatment (PWHT).