FredlyFX

Heat treat for AR500

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Hi guys, long time no see. Life has been kind of crazy.

I've had a little job come up helping out my local shooting club. They have a target that is made from 3/8" thick AR500 armor plate. Someone shot it full of holes with some kind of magnum and I want to try to fix it.

Another guy already welded up the holes once, but his welding just tempered the plate and so everwhere he welded it the plugs came out and other holes showed up.

I have a couple of questions.

1. What would be the best stuff to weld it with? I have a 225 amp buzz box and a 175 amp wire feed welder. Which rod or wire would hold up best and be able to be heat treated along with the AR500?

2. Once I weld the holes and grind everything flat what should my heat treat process be? How hot, how long and what quenchant should I use? Also, does it need to be temperd afterwards or should I leave it dead hard?

Thanks for any input you can offer.

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Find oiut what company made the steel and ask them for heat treat advice,,welding suppoier should b e able to get the rest

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Thanks for the info guys, but I was hoping someone actually knew how to do this. The links you gave me Frosty were interesting, but they didn't give me any real heat treat info. The database is $149 for a 4 week trial.

My plan is to weld the holes with 7018 and then heat to orange and quench in veg oil. Any idea if will shater the metal or if anyother bad stuff might happen? Or, is this stuff air hardening?

Thanks

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Did you try searching yourself? I only posted a few of the first hits I got.

I have no idea, sorry.

Frosty

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Hi Frosty,

yeah, I have done a bit of searching, but not gone into full fleged mission mode yet. I was just gathering some info hopping someone just knew how to do it. So far I have seen a lot of conflicting info or questions about welding it, but no real info on heat treating it.

One suggestion that would make sense was to use a low heat TIG with pure Argon. The problem is I don't have a TIG set up. I also have the problem that it has already been overheated by the previous welder.

My thought was to just use 7018 and then do a heat treat with veg oil. The real problem for me is that I am totally guessing here.

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AR500--Isn't that the steel that is used on Dredge buckets and other digging buckets? If so, there is this build up rod that is used to repair worn spots to be used under the hard facing. This build up rod may be what the Doctor ordered.
Warren

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I have some experience with welding AR400...and I'll go out on a limb here and assume AR400 and 500 are similar. I know that welding the 400 with a mig does no good, not enough penetration. You can tack it with a HOT mig, but that's about it. My experience is to arc weld it. Perhaps this could be the reason the plug welds came out? 7018 rod seems to be the one to use.

Edited by Golden_arm

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I own one of these targets, it's supposedly rated for the 50 BMG. Makes me wonder if somebody was using armor piercing rounds on it. If so, there isn't much to stop such a thing. Seems like the retailer of mine said it had a brinnel hardness of 500 or some such. Law Enforcement Targets, Inc. - Steel Silhouette Targets . My though isn't terribly scientific but isn't the greatest hardness achieved through the fastest quench from critical temp? These plates aren't supposed to be "tough" so much as hard. The angle they hang at is intended to ricochet the bullet into the ground in front of the target stand.

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Unfortunately there is no uniform specification for AR500 material other than hardness and the chemistry and Heat Treatment will vary from mill to mill. A representative chemisrtry is C-.30%, Si-.70%, Mn-1.70%, Cr-1.00%, Ni-.80%, Mo-.50% and B-.004%. Surprisingly the Boron @ .004% has a huge effect on the hardenability of the steel and an even bigger effect on the response of the Heat Affected Zone. In the HAZ where the temperature is in the 600F to 850F range the impact strength of the material can decrease to near zero due to the presence of carbides and untempered Martensite. We have learned this the hard way from Bainitic Frog Castings we have produced by adding Boron to induce Bainite. These were being investigated as an alternate to Cast Manganese Steel (Mn-14.00%)

I don't think that you will be able to restore the strength and hardness of the repair unless you utilize a Hard Facing material with an as-deposited hardness similar to the AR500. If this material is used however the HAZ will likely crack due to the highly restrained nature of the "plug weld" and influence of the Boron.

If the repair can be made sucessfully, reheatment of the entire target may be attempted. The structure of AR500 is tempered martensite which is obtained by a quench and temper operation. This should be accomplished by heating the material uniformly above it critical temperature to fully Austenize the structure. A starting point could be 1625F to 1675F and time at temperature should be about 1 hr per inch of thickness or in your case 20 to 30 minutes. Quench the material in light oil heated to 150F. After quenching test the material using a file. The file should skate across the surface and not cut the material. If the material is soft reheat and quench in cooler oil. While it may be necessary to obtain a faster quench, a water quench will most likely result in a cracked plate.

After the plate has been quenched it must be tempered, using the plate without tempering risks the plate being shattered and creating shrapnel when struck by a bullet. The harden plate should be tempered to 350F to 400F for one hour after reaching heat. Check hardness using a file and comparing to an unaltered plate. Be prepared to do all of this again if it is too hard or too soft. Remember too hard - raise the tempering temperature, too soft - lower the temperature.

If with all this effort the plate repair plug doesn't fall out on it's own, the plates don't crack and the hardness is okay, the repairs may still be punched out if a round hits the same spot.

Good luck with your efforts. I also shoot pigs and chickens. I use a .22RF and a .22 Hornet in a Contender fitted with a 20X telescope.

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I am confused here. You have a plate that is harder than woodpecker lips that is full of bullet holes. You want to weld the holes up with a soft material like 7018? Won't that just let high power FMJ bullets just punch right through the welded up holes? Even using a rod made for AR500, I think you have a similar problem. You took on a tough problem, Fredly! Good Luck!

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