Shouldn't be too much on mild steel. If it was chromoly, it would be necessary for sure. I took my time for proper cooling. You can see in the haz zones there aren't any weld much over an inch or two.
Most of the weld kits for trailing arms don't specify any stress relief on mild.
Maybe a metal head like
@WARRIORWELDING,
@Mac5005 can chime in.
Matt
Awesome work Matt. I've definitely been following along, and love every update.
Here are my thoughts on above.
The required temperature and cooling methods are expensive and labor intensive. To get any benefit from post weld heat treatment, it is critical to not only heat to the proper temp, but also cool as a specified rate. If done incorrectly, you can easily do more harm than good.
The normal temp range for stress relieving mild steel through post weld heat treatment is anywhere from 700-1000 deg C, and a soak for 3-4 hours.
This is above what most powder ovens are capable of, and is exactly why the powder coating process. doesn't typically affect the parts metallurgy.
If you could get an engineer to spec out the process for the thickness and material used, it would be great to have it done, but i also think that cost would far outweigh the benefit.
Looking at all the pics, And knowing matts attention to detail, I know the fit up and prep on all the pieces was perfect.
This ensures the resultant stress are as low as possible after the weld cools and shrinks.
The other consideration is that the trailing arms are of significant thickness material and have adequate thickness in each plane through the cross section. This counteracts the shrink experienced from welding.
For those following along, the residual stress is from all the shrinking of all the welds in all the different planes.
A better more practical and cheap way to keep residual stress down in an assembled and welded part, is to ensure that the base metal, within .5" from edge of HAZ, stays below 400 degrees F. This ensures that the weld time is short enough so that the HAZ size and temp don't get crazy out of control.
To add to that, would be to practice your weld technique on an identical joint and destroy it to test the strength.
The benefit from a quality weld technique and proper puddle manipulation is far greater than any PWHT and stress relieving, as far as bang for the buck goes.
From what I see, matts welds look great, and the HAZ looks fine.
If it were a no holes barred race car, with an unlimited budget, then the arms would most likely be 4340, and PWHT would be mandatory.
Here is a good link that offers a basic explanation:
Heat treatment of welded joints - Part 1 - Job Knowledge 114
I am curious to hear thoughts from
@WARRIORWELDING @MarsFab and
@stinkbomb.
