I am executing the gas tungsten arc welding of Inconel 718 sheet metal of thickness 1.5 millimeter. I found minor cracks in the weld metal. What can be root cause of these defects and how to avoid it?
I used ERNiFeCr-2 filler metal of size 1.6 millimeter. Pulsed GTAW was employed. THe component is a duct made of sheet metal. No external fixturing was used.
Try to reduce an arc voltage a bit (~1V). The weld bead will became more rounded, reducing a stress concentration, so other factors which can result in same cracking problem (i.e. contamination, bad shielding etc.) will have a lesser effect.
Cracking within the weld metal may also be due to segregation of allowing elements such as niobium and boron as the weld solidifies meaning there are nonuniform mechanical properties across the weld. For the cracks to form there must be some sort of stress on the weld area and this is most likely thermally induced residual stress so changing the restraint on the weldment may help. I'm sure there would be some published research relating to your problem available online. Try the following links as a start:
https://www.google.com.au/url?sa=t&source=web&rct=j&url=http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/29/018/29018458.pdf&ved=0CCkQFjACahUKEwj_59WfwO7HAhVE4qYKHeSnAJk&usg=AFQjCNG2-AYlShcRpBTt6Q6jF-0MaDW8yg&sig2=k7Lv_QFsGoW5glWyw8jmfg
https://books.google.com.au/books?id=p9VwAgAAQBAJ&pg=PA175&lpg=PA175&dq=inconel+718+weld+segregation&source=bl&ots=Br_zZdtcWa&sig=5dqJiKeltsh5G5nIpGQyLrt-qSA&hl=en&sa=X&ved=0CDgQ6AEwBWoVChMI_-fVn8DuxwIVROKmCh3kpwCZ
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