Armor plate

[Sludge]

Ok guys. Im sure as wide of an experience pool as we have here that some of you have worked with metals.  To you guys, I have a question. 

Ive had a plate of 3/8ths thick AR500 laying around here for some time.  I want to make some rifle and pistol targets out of it.  I have a plasma cutter, but have been hesitant to cut it for fear of changing the properties of it in the heat affected areas surrounding the cut.  Ive considered taking it to someone with a submerged plasma cutter or perhaps even to a water jet.  The water jet would no doubt be the best option but time on those machines is expensive and this stuff is likely going to be a slow cut.  I could sink a pile of money into getting it cut up. 

Am I worrying about nothing?  Should I go ahead and cut it or should I just throw down the cash and have it cut for me?

Thoughts?

[rodeo1]

if you are building a space shuttle then i would worry about it (maybe) if you are building targets -- what do you care about the "properties" if it bitches -- SHOOT IT !

[designer]

AR500 is the top end of the target metals, Cut in short burst and cool between and you should be ok...   If your planning on hanging the targets its your welding process that will anneal the metal more then your plasma cutter.  Most hanging target give at the welded joint with the chain.

www.agarms.com/pdf/steeltargets.pdf

if your cutting process anneals the metal it will only be the outside 1/2 to 1 inch perimeter. 

[Gryphon Rider]

A quick Google search provides an answer, from the Yahoo! group "plasmacutting":

Hello,
I'm new to plasma I don't know how the AR would affect cutting on a DIY
CNC table. Could you tell me if the Hypertherm 1650 will cut AR500 3/8"
at 100% duty cycle? Could the 1250? This would be for short run
production.
Thanks for the help, Shepard
Shepard,

AR500, which is a quenched and tempered wear resistant plate…often used as armor…is easily cut with plasma. Because this plate will tend to soften if heated then allowed to cool slowly…plasma generally does a better job at maintaining the base hardness due to the minimal heat affected zone as compared to oxy-fuel cutting. Their will be a little softening near the cut edge due to heat input….and with air plasma such as the Hypertherm Powermax1250 or 1650 their will be kind of a case hardening (maybe .005” or so thickness) directly on the cut edge due to nitriding (an effect caused by the nitrogen content in the air)…as is the case on all carbon steels cut with air or nitrogen plasma.

The plasma…from a duty cycle perspective… will not know any difference between this material and a standard A-36 grade steel. Either the Powermax 1250 or the 1650 will do a good job. To eliminate the nitriding…you would have to either gring off about .005” after cutting…or cut it with an oxygen plasma such as Hypertherm’s HSD130 or HPR130 system.

Jim Colt

[Bobbo]

If you don't mind taking a little more time to cut it, an abrasive chop saw might be a better choice.  A plasma cutter might anneal a tiny area next to the cut, but shouldn't affect the majority of the plate.

[Ferris Leets]

Unless you cut really slow the chop saw will put in more heat than the plasma.  The HAZ from plasma cutting is VERY small.  I've done a lot of cutting with plasma and it will not bother your AR plate enough to consider.  Unless you are building a Space Shuttle and in that case 3/8" AR is way to heavy!!!!!

[Bobbo]

Unless you cut really slow the chop saw will put in more heat than the plasma.

That's why I said "if you don't mind taking a little more time to cut it".  If you make a continuous cut, to the point where the steel glows orange, you are potentially removing the hardening.  With a chop saw, you make a small cut, then let the steel absorb the localized heat before continuing.  If done properly, there will be no bluing of the steel.

[Sludge]

if you are building a space shuttle then i would worry about it (maybe) if you are building targets -- what do you care about the "properties" if it bitches -- SHOOT IT !

Well, I would like for it to hold up properly.  I may sell some of these if it works out ok. 

If you don't mind taking a little more time to cut it, an abrasive chop saw might be a better choice.  A plasma cutter might anneal a tiny area next to the cut, but shouldn't affect the majority of the plate.

Well, its hard to make round shapes with a chop saw.  I plan to cut some round plates for a plate rack, some pepper poppers, parts for a dueling tree, a texas star, and a polish plate rack.  Then some IDPA sized targets and some plates for long range rifle work.