Why do I have cracks in the parent material?

Cracks appearing in the parent material around the weld nugget can be caused by several issues. They are:

High Weld Force – can fracture the parent material with excessive forging action.
Insufficient Cooling – Over heating can cause excessive stresses from expansion and contraction along with the forging action.
Metallurgy of Material Welded – Some materials become brittle at the temperatures experienced in resistance welding.

Other factors that could cause fractures are small electrode face areas and short hold times.

A sketch of surface cracks is illistrated in AWS D8.1 Figure 2 shown here:

D81 Surface Cracks145

 

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