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I Forge Iron

hardened edges on plasma and lased cut steel plate

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Every now and then I will purchase plate drops from my local metal supplier.  On acouple of occasions I have encountered hardened edges.   In a couple of cases the edges were hard enough to destroy the usefulness of a band saw blade.  Is this a comon problem ? 

Just wondering how the best way to test for hardness before starting to cut and how deep to expect the hardening to extend away from the edge.  

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Laser isn't usually quite as bad but with plasma there will virtually always be a hard heat affected zone.  Most plasma systems use dry air as their cutting method so are actually burning material and that can cause both hard oxides as well as plain old carbon-hardening at the edges.  With laser, they tend to use nitrogen and blow the kerf rather than burning the kerf so you don't get quite the same HAZ..but there is still some.  Rarely, plasma will also use nitrogen and blow the kerf but that's pretty expensive for basic plasma cutting.

SOP for machining such things is 1) grind the entry point through the HAZ so you start cutting in "fresh" material and 2) when machining (most often profiling), you make sure your depth of cut is plenty to always be cutting in fresh material--and always conventional cut rather than climb cut so the endmill isn't diving into the hardened surface...it's always coming out of the softer material to remove that HAZ.

Sawing basically the same although most people are lazy and only grind the infeed point.  Best on the blade if you also grind the HAZ off the exit point too.

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JHCC thanks for the reply.  Well, yes I did do a file test, and the cuts are clean with no slag.  Basically, at least from this source I will need to assume increased hardness from this supplier and start and finish the cuts with abrasives.   I tried to anneal the metal in my oven without  success so it could be an alloy . I called the supplier - they were clueless.  

Thanks Kozzy.   Yeah I guess I just need to accept the hardness and grind finish and start to accomoate a good source of materials. 

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