Steel Breaking when bent

[RAYZORcut]

Cut some brackets out of 1/4” x 6” cold rolled flat bar, customer went to make a 30 degree bend on one of them and it broke. Would this have anything to do with the plasma cutter creating a more hardened material from the cuts or is this a CRS issue?

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[tinspark]

It might be his method of bending.
The standard bottom die opening per SMACNA is 8 times the metal thickness, So a 2” bottom die is the norm for .25” material with a standard top die (aka punch)

[acourtjester]

I know the edges are very hare but should not have caused the problem of him bending. You may try a short line cut where he wants the bend and he can weld the line close after bending. Many cut bending lines to help show where to bend and make a more sharp bend too.

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[SegoMan DeSigns]

Was it bent at 90* from the grain of the metal?

[RAYZORcut]

I’m not sure about any of his bending procedures but it is 1018 cold rolled flat bar. I’m aware that there is hardening (with metal in general when plasma cutting) but usually very minimal not enough to cause this I would think, so I’m beginning to think it’s the 1018, I’m coming to the understanding I should be using CR 1008 for requesting customers who want to bend or manipulate CR.

[TJS]

Yes it is the cold roll. Try hot roll plate it should work.

[hardworker]

I have purchased semi loads of flat stock hot rolled steel an found that if its bent (with the grain per say) its just fine, but for example taking a 3ft piece of 1/4 x4" flat stock an trying to bend a formed 2x2 angle with it does not work 90% of the time no matter the die radius, it always seems to crack. maybe possible to preheat prior to bend... if your out of options. That's just what I've ran into over the years.

[RAYZORcut]

Thank you everyone for the input, going to be getting some 1008 cold roll and mild steel hot rolled A36, same cuts and will see how it goes. I will post back to let all know how it went CHEERS!!

[jimcolt]

A plasma cut edge on carbon steel when cut with an air plasma torch develops a nitride hardening. This hardening is caused by the (roughly) 80% nitrogen component in the air we breath. Most cuts will leave an approximately .006" hardened depth.....and if you make a few light passes with a flap disk grinder the hardened edge is removed.....and the chance of cracking will be gone. The high end XPR plasma's can use pure oxygen as the plasma gas, which eliminates the need for grinding. Unfortunately an air plasma must use air as the cutting gas (do not attempt to use oxygen in an air plasma, torch damage and / or torch and leads fire will cause damage). Only use oxygen on the high end, liquid cooled XPR or High Definition industrial plasma cutters. Jim Colt

[RAYZORcut]

Thanks Jim, I will give it a go. I’m guessing this would be the same issue for different materials as well. Hot Rolled, Stainless, Aluminum, Cold Rolled etc… ? Doesn’t matter the grade either? As stated that was 1018 CR , I was going to try 1008 CR. Cheers!!!

[jimcolt]

Mild steel and carbon steel terms cover most steels including different alloys and surface finishes (so hot rolled, cold rolled as well as high carbon and Abrasion Resistant (AR)) will typically all cut similarly with an air plasma cutter, and will show the same general effects on nitride surface hardening. Stainless and Aluminum will typically no show the same type of hardening. Jim Colt

[RAYZORcut]

Very useful info.
Cheers!!