metallurgy- bed frames + plasma cutting = bad

I like to post about my experience to warn other that may attempt simullar things.
I need to add weld some angle iron pieces as spacers or retainers
in a non critical application, any metal angle pice would have worked just fine , I did not want to waste fresh angle irons (mild steel,) so I reached for some bed frames I picked up for free a while back , for this kind of purpose.
I ended up cutting the hot rivets of with a plasma cutter , also making some minor cuts. and holes with it.
than I had to cut nice 1.5" pieces so I used a wet- horizantal bend saw. all went fine , cut a couple pieces, than came the throuble
I've noticed that the saw has been cutting the same piece for a fairly long time. ..... it actually got stopped right where one of the plasma cut whole was. the band saw arm would not budge, I thought it was stuck on something , So I applied light pressure to it. still nothing.
I flipped the piece around and started cutting it from the other side of the angle piece, again it was cutting fine till it reached the whole which was plasma cut, got stuck again.
conclusion, on the spot where the plasma cut was made on the bed frame , the metal got extremely hard , a regular blade would not cut it.
actually the blade got ruined. lesson learned.
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Yep, high carbon and a HAZ equals REALLY HARD!! I've had the same problem with some (supposedly) mild steel bar stock. One piece of a stack had way high carbon, welded it up, went to cut the pieces in the saw, took out THREE blades before someone stopped the carnage.
acrobat-ants wrote:

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Don't know if it's the same where you are, but here in the UK a lot of bed irons were made from recycled tram and train rails, to give high strength in a light cross section, and I understand that it has a high manganese content to make the surface work harden. When you cut with the plasma the surrounding metal will have cooled the h.a.z. from molten to cold very fast so it will be glass hard as though you had water quenched it.
AWEM
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Bed frames are made from spring steel, not mild steel.
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I think you will find that most all steel that is cut with a torch, plasma cutter, or chop saw using abrasive wheel will leave a very hard area at the cut line. It is always best to factor this in when planning your cuts. One place where I buy steel tubing and hot rolled steel bar stock will cut pieces for you. They use a very large chop saw. Very noisy, dirty and lots of sparks. It leaves the cut line very hard. I allow for about a 1/4" waste at the cut line to be on the safe side. Measure twice.......cut once.

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We had some 3/8 A36 plate plasma cut and pierced. The dozens of 5/16 holes were then to be drilled to 3/8 using new cobalt bits. Three bits later ($$$ouch$$$) we started removing the haz coating with a die grinder and a carbide bur and it cut like butta!
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