Failure Rectangular HSS Tube Resistance Weld

[roberthathaway]

We use a 5/16" thick 110 ksi min. yield hss material formed into a rectangle and resistance welded to form a frame rail. A pair of these tubes combined with cross members makes up a chassis. We are experiencing localized fracture in the throat of the weld initiating at the weld crown. Starts ductile and goes brittle. Looking at 350 Knoop hardness in the fusion zone. Has anyone experience such a failure?

 

[EdStainless]

What is the alloy?
How is it heat treated after welding?
What NDT is done on the welds?
And a hardness profile across the entire weld into the base metal would be helpful.
As well as some photos.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

Check the weld size. Throat failures can be caused by undersized welds.