Understanding Weld Cracking
Weld cracking occurs when thermal stresses exceed material strength during or after welding. Understanding risk factors enables preventive measures.
Types of Cracks
- Hot Cracks: Form during solidification, caused by impurities or high restraint
- Cold Cracks: Form after cooling, hydrogen-induced, delayed cracking
- Crater Cracks: At weld termination, from rapid solidification
- HAZ Cracks: In heat affected zone, from microstructural changes
Material-Specific Risks
- Carbon Steel: Highest risk, especially above 0.3% carbon
- Stainless Steel 304: Low risk, austenitic structure resists cracking
- Aluminum: Moderate risk, hot cracking from alloy segregation
- Titanium: Moderate-high risk, requires inert atmosphere
Prevention Strategies
- Preheat: Reduces cooling rate and hydrogen diffusion
- Low Restraint: Design fixtures to allow thermal expansion
- Proper Sequencing: Weld order affects stress distribution
- PWHT: Post-weld heat treatment relieves residual stress