American Welding Society Forum
I have a client that is welding trunnions to log truck trailers, they have been having issues with the welds detaching from the base metal. After performing a chemistry test the results are below. They would like to still use these trunnions but arent sure what filler metal to use. They have been using an E71T-XX filler metal with no problems intil they received this batch. And recommendations would be great. Thanks
Any help would be greatly appreciated.
The chemistry indicates this base metal could be quenched and tempered in which case welding isn't highly recommended.
The manufacturer should be contacted and politely asked for their recommendations.
This is a very late reaction. But I need to satisfy my curiosity:
Question: How can I tell from the metal chemistry that the metal could be quenched and tempered?
Thanks for the further enlightenment
It is a low alloy steel based on the chrome, nickel, molybdenum and the boron indicated by your listing of the chemistry. The carbon puts it up in the range of a medium carbon steel. Taken together, this would be a hardenable steel. In the hardened state, it would be strong but brittle, so it would be tempered to reduce the hardness and strength to a small degree, but it would improve the toughness and impart some ductility.
The heat treatment of the "lot" may have been different from the typical shipments of steel received from the supplier. Perhaps a new supplier was used that used a different heat treatment or possibly the tweaked the chemistry in comparison to other shipments. Let's face it, purchasing agents are always looking for the "deal" that will save money. They don't always appreciate the repercussions of minor changes in chemistry or heat treatment.
Another possibility is the filler metal was exposed to the atmosphere long enough to absorb moisture, thus introduce hydrogen into the weld and HAZ. Think of FCAW electrode that has been left on the wire feeder over a long weekend in humid conditions. FEMA limits the time a spool can stay unprotected to 8-hours in a seismic region if I remember correctly.
Most truck frames of modern tractors are quenched and tempered. Generally the manufacturer will prohibit welding of any sort in behind the front spring hanger to the far back of the rear spring hanger. That area, between the front and back wheel sets see the highest stresses and Q&T steels are degraded whenever they are welded or subject to high temperature above the tempering temperature used by the manufacturer.
It would make sense that the trailer manufacturer would use similar materials for their trailer frames, i.e., maximize the mechanical properties and reduce weight so they can haul more product.
The material (Q&T steel) is very sensitive to hydrogen assisted cracking. I would expect the cracks to initiate in the HAZ of the weld to the Q&T frame. The WPS must be properly developed and followed to the "T". Slow cooling to ensure the HAZ isn't too hard and more sensitive to delayed cold cracking (hydrogen assisted cracking), but not so slow that the mechanical properties of the HAZ are substantially different than the expensive Q&T steel with the "great" mechanical properties. Designers often look at the mechanical properties and pick the highest strength because they can reduce the thickness and save weight. What they fail to appreciate is the difficulties those same steels bring to the table. And to the uninformed welder; steel is steel and it will rust if it isn't painted.
I would recommend that you take a section and have failure analysis performed. St. Louis Testing is a great lab or Structural Integrity out of Austin Texas.
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