Scale formation
A scale spot is a localized oxidation on the weld surface or in the HAZ, caused by insufficient shielding gas coverage during cooling. It impairs corrosion resistance and can lead to cracking.
Physical-Chemical Mechanism of Action
The scale (oxide layer) forms when oxygen contacts the weld metal or the heat-affected zone. Without sufficient shielding gas post-flow during cooling, oxygen can reach the surface and start oxidation.
Metallurgical Relevance & Welding Risks
Scale impairs the corrosion resistance of the component because it provides a starting point for further rust formation. It can also lead to local cracks and reduce mechanical strength.
Workshop Practice & Instructions
To avoid scale, it is crucial to ensure sufficient shielding gas post-flow during the cooling process. This can be achieved by correctly setting up the shielding gas concept and using high-quality shielding gases. A typical post-flow time is at least 5 minutes after finishing the weld.