Plasma cutting

[Bradrock]

Does plasma cutting steel weaken it? I have rough cut the strut attach bars with a plasma cutter, but don't have much experience with this method.

[X'N]

I'm no expert by any means but I would think it could possibly cause more stress around the cut. I would normalize the pieces to be safe.

[Mark Goldberg]

We have only plasma cut parts that are then going to be welded around their entire perimeter. The plasma cutting does leave a bad edge. How much would need to be removed to take off the effected edge that can cause problems? - that is for someone with more knowledge. Mark

[Battson]

Around the cut there is a region known as the HAZ (heat affected zone). Welding also creates a HAZ. ​The size of the HAZ varies with the temperature the metal reaches, so a longer or hotter cut (or weld) tends to result in a larger HAZ. ​Exactly what happens in the HAZ depends on the many factors, and it's more than is worth discussing here. Safe to say Oxy welding, Plasma cutting, and TIG welding all create a different sort of HAZ.
The metal in this region has a different microstructure to the base metal, and will have less favorable properties i.e. increased brittleness (lower ductility), which makes it susceptible to cracking depending on the exact properties of the HAZ (related to how it was created). Cracks that start in the HAZ will normally propagate along the HAZ-base metal boundary or into the base metal. Welded parts breaking beside the weld bead is a classic example of cracks propagating through the HAZ.

I would tend to use a cut-off disc ahead of the plasma cutter, for aircraft applications (unless your doing a destructive disassembly), just to avoid altering the base metal's properties. But I am not a materials expert! I do think that once you get into normalising welded / cut areas you're effectively re-engineering the metal's microstructure and hence properties.