It's about the grain sizes and intergranular changes because of welding i think
After welding you will see a lot of different sections that are affected by heat differently.
In most applications weld metals have fine grains due to recrystallization and tempering effects of the upper beads
[And so upper sections of the weld metal have bigger grains (because they are less tempered)]
In the fusion line there is a non-complete fusion section (grain structure is like a casting)
After that, in HAZ a highly heated (but no fusion) big grain size section comes near the fusion line
This section is the most risky one. In most cases if corrosion cracking happens it does it here.
This doesn't mean that weld metal behaves more noble than base metal i think. the corrosion is between the weld metal and HAZ
I didn't see anywhere anything certain about the causes of this type of corrosion.
Ali Asghari yazmış:
hiwhy corrosion occure preferentially in haz ,especially fine grain location?why weld metal noble than base metal?regard advance
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