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: Risk increases with carbon equivalent, restraint, section size, and cooling rate.
- Stainless Steel 304: Often lower crack sensitivity, but heat input, restraint, and sensitization still need review.
- Aluminum: Hot-cracking risk depends on alloy, filler choice, joint design, and dilution.
- Titanium: Shielding coverage and hot-zone exposure should be verified before release.
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