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Author: Subject: [Metalurgy] Homemade steel body armor
joseph6355
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[*] posted on 2-1-2018 at 19:40
[Metalurgy] Homemade steel body armor


Is anyone interested in the idea of making their own steel body armor?

First of all, lets pay attention to some principles when making hard body armor.

A lot of people talk about ar500 and ar600, but those are industrial nomenclatures, and not actually steel chemical standards. It means that ar500 isn't actually a steel alloy, but just a market-friendly way of describing a certain type of steel that has been exposed to certain heat treatments.
AR stands for abrasive resistant. It means that there are chemical additives (alloys) that are mixed within the molten steel in order to achieve resistance to abrasion (it will suffer less from wearing when scratched with a harder element). Generally, Manganese, Phosphorus, Chromium and Boron are added in certain quantities to obtain such characteristics.
500, 600 and so on, stands for the Brinell hardness of the metal. 400 is not enough if you want it to last, 500 is ok, 550 is good, 600 is ideal if you chose the proper thickness for the armor plate. Don't go above 600 or else it will get so brittle that it will shatter (specially after a few shots from a heavy hitter). Choosing the proper steel alloy is the key. The most important factor to stop a projectile is the final hardness, but the added alloys also imply in a greater bullet-stopping capability, specially Manganese and Phosphorus in higher quantities, and also add toughness to the hardened steel so it is hard but not as brittle as other less tough steel alloy would be at the same hardness.

Steel alloys
The most easy-to-get steel alloy that will suit these needs is the AISI 5160. It is frequently used in leaf springs, so it became readily available and cheap. At 600 Brinell, you can get away with .210 gauge thickness, but back face deformation will also be greater, and thus, increase the chances of an injury. The pro side is that it will be slightly lighter.
I would personally go for the 1/4" thick plate, it will be more robust and last longer, and also compensate for any human error that could be made that would reduce its bullet-stopping capabilities. Another key factor is grain refining. Normalizing the steel will reduce the grain size and increase the plate toughness, because the kinetic energy delivered by the projectile will be more evenly distributed among the greater number of grains. Think about it as hitting a bucket filled with fine sand with a hammer, and then hitting another bucket filled with gravel. Which one do you think that will result in a higher penetration depth? :)

Heat treatment
In order to heat treat it correctly, you could send it to a heat treating company. But it would totally defeat the "homemade" purpose of the thing, right? You could build a gas forge, and judge color by the eye.
Not a very accurate reading, but if its the best you can do...
AISI 5160 is very forgiving when heat treating though.
You will need to heat it to a red-orangeish color and then let it cool to black, and wait a few minutes then. Do it 3 times.
Next, heat it again to the same color and quench it in a fast coolant, like olive oil or parks 50 oil. Agitate it gently.
Next, put it in the oven and use an accurate temperature reading, like a good thermometer. Temper it to 200-210 ºC for 1 hour, and then let it cool to room temperature.

And remember to curve or form the plate before you heat treat.
A lot of companies complain that 600 Brinell steel cant be bent and curved, so they don't use it.
Well, they shouldn't be bending the hardened steel in the first place, it will cause a lot of stress in the material and compromise toughness.
All forging, curving and cutting should be performed prior to normalizing and hardening.
The true reason why they do this is because they buy the steel from a proprietary company that don't disclose the alloy used neither how to heat treat it, and then they don't have other option but to curve the hardened steel.
Common abrasive resistant borderline-proprietary alloys used in body armor are T1, T2, T3 and so on. AISI 5160 gets very close to some of these abrasive resistant alloys, and it is both tough and capable to achieve high hardness.

Thickness
First of all, lets talk about what the NIJ standards call for.

https://www.ncjrs.gov/pdffiles1/nij/223054.pdf
Type III hard armor or plate inserts shall be tested in a conditioned state with 7.62 mm FMJ, steel jacketed bullets (U .S. Military designation M80) with a specified mass of 9.6 g (147 gr) and a velocity of 847 m/s ± 9.1 m/s (2780 ft/s ± 30 ft/s).
That is what a level 3 body armor should be able to stop.
Commercial body armor are mostly 1/4" thick and have a hardness of 500 to 550 Brinell. At this hardness and thickness, it will stop most projectiles traveling under 2900 ft/s (for 5.56) and 2800 ft/s (for 308 win).
Newer plates though have an increased hardness at about 600 Brinell, and some going even further till 650 Brinell.
Spartan armor plates have a thickness of .210 inches, and 600 Brinell hardness, and will stop 5.56 projectiles traveling under 3200 ft/s. That is a huge improvement, since a 55 grain projectile traveling that fast would penetrate a common ar500 plate.
The problem with a hardness like this is that the plate will be prone to shattering. To counteract that, we can try to refine the grain and increase the thickness. A thicker plate will accept an increased hardness better.
It is also proven that ar500 1/2" thick plates will stop a .50 BMG FMJ traveling under 3200 ft/s. But if you are going to get hit with a .50 BMG, the kinetic energy itself would probably kill you anyway, because there isn't enough surface are to distribute this energy that would allow it to be reduced to an acceptable level. So just take your armor off and die like a man. :)

Anti-spalling coatings
You can always pay someone to coat your plate with bedliner. There are places that will offer this kind of service. But I'm gonna focus on the fun part, which is making it yourself.
You could coat it with bedliner yourself, but it is kind of expensive, messy and complex. So we will use fiberglass.
You see, fiberglass and epoxy are perfect for this. The final product will be a hard plate that will not only help with slowing down the projectile, but contain its spalling.
The projectile will penetrate the fiberglass plate and hit the steel, which will make it basically pulverize, but the surrounding fiberglass will catch all of the fragments.
The fragments usually fly at a 20º angle from the plate, so I eyeball a 1/2" thick fiberglass plate to be enough to catch all the fragments.


I think I covered the basics and now we can start a discussion about it. Maybe testing too.
I can't test it with rifles because I live in a country where it's not possible to own it legally, but I'm sure that there are a lot of Americans here that can test it properly.
I've shot a small 10x10 cm plate before with a .38 SPL and .40 SW. No dents, no bending, no back face deformation, no nothing. It wasn't even fun. :(

[Edited on 3-1-2018 by joseph6355]




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elementcollector1
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[*] posted on 3-1-2018 at 09:32


Honestly, if I were going to build a set of body armor, I'd make it from UHMWPE. Far lighter, and just as strong.



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[*] posted on 3-1-2018 at 09:45


Is it just me who thinks this makes roughly as much sense a a DIY parachute?
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[*] posted on 3-1-2018 at 09:53


how are you creating your steel alloy plate in the first place? if you are already buying a steal plate, why not just buy a bullet proof plate?
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[*] posted on 3-1-2018 at 10:41


Quote: Originally posted by elementcollector1  
Honestly, if I were going to build a set of body armor, I'd make it from UHMWPE. Far lighter, and just as strong.

I don't know. I hasn't been tested.
Are you sure it will sustain multiple hits from a 5.56 projectile traveling at 3200 ft/s?




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[*] posted on 3-1-2018 at 10:46


Quote: Originally posted by walruslover69  
how are you creating your steel alloy plate in the first place? if you are already buying a steal plate, why not just buy a bullet proof plate?

For the sake of experimenting and creating something with my own hands.
What if some day you are not allowed to buy armor plate anymore? What if the government requires it to have a serial number? What if...
Nothing wrong with testing and having the knowledge.

I don't want to depend on the government or any private company to protect myself from rifle threats.

"why not just buy a bullet proof plate?"
Why buy it in the first place if I can make my own?
It will be far cheaper and have the same efficiency.




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[*] posted on 3-1-2018 at 10:58


Quote: Originally posted by unionised  
Is it just me who thinks this makes roughly as much sense a a DIY parachute?

Yeah, lets just rely on the government and private companies to protect ourselves.

Nothing wrong with going online and buying a steel plate. But remember that not so long ago it was possible to buy nitric acid otc, nowadays it became more expensive and hard to get, forcing people to make their own.




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[*] posted on 3-1-2018 at 11:42


Quote: Originally posted by joseph6355  
It will be far cheaper and have the same efficiency.

...Somehow I doubt that.

I'm not sure what you're trying to do here. Are you trying to make medieval plate armor that's bulletproof?

If you do and you can demonstrate it works just as well as commercial products, definitely post it here. It would be quite the achievement.
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[*] posted on 3-1-2018 at 12:48


Quote: Originally posted by joseph6355  

You will need to heat it to a red-orangeish color and then let it cool to black, and wait a few minutes then. Do it 3 times.

What would be the purpose of this? Normally one only needs to heat to uniform heat plus 15-30minutes soak time.

Quote:

Temper it to 200-210 ºC for 1 hour, and then let it cool to room temperature.

This will most likely produce a brittle product. While I haven't worked with 5xxx steel I do know a little bit about 4xxx, and it is seldom annealed below 400°C.




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[*] posted on 3-1-2018 at 12:59


you could just stock up and buy plates. they are less than $100. You wont be able to make anything like that for $100. You never answered, how do you plan on making the steel alloy plates in the first place?
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[*] posted on 3-1-2018 at 13:34


Quote: Originally posted by joseph6355  
[
Yeah, lets just rely on the government and private companies to protect ourselves.


I guess you make your own bullets, make your own powder + make your own guns too.
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[*] posted on 3-1-2018 at 13:52


@joseph6355 Don't listen to the nay-sayers. Have a go.

Its right there are the top of the page: "The Art and Science of Amateur Experimentalism". I'd have thought everyone would be more supportive.

I build or make a lot of stuff I could just go out and buy - but where's the fun in that? What would I learn?

[Edited on 3-1-2018 by Twospoons]




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[*] posted on 3-1-2018 at 15:34


Support should not be conflated with encouragement. What I am seeing are people supporting the OP in a way that ultimately leads away from a misguided effort to solve a problem that does not exist using methods that are likely to be flawed and inefficient, perhaps even ultimately dangerous.

I appreciate the ‘do-it-yourself’ mentality, not for a conspiratorial distrust of large organizations but for a sense of self-improvement and satisfaction. However, in the context of this thread, how much chemistry and how much ‘make-it-yourself’ is actually involved? In my opinion, not much.

In order to experiment and learn, you would need detailed knowledge of the chemical composition of the steel being used. This requires it to be purchased from an organization that can provide material test reports that are generated in accordance with large, untrustworthy organizations such as NIST, ANSI, ISO, etc. That aspect removes the majority of the DIY.

Where will you get your 5160 steel from? Can you guarantee the beat up old Chevy that spring steel was removed from is indeed 5160?

How will you control the heat treating process on something you are entrusting your life to? I used to work at a shop that made gear components for limited-slip differentials. The gears required a combination of through-hardening for overall toughness with a case hardness at a critical depth (too deep and the whole tooth was brittle, too shallow and it would deform). The heat treating process is difficult to control, and really more of an art form with myriad variables. Our vendor was really quite good and yet we would still see over 50% failure rate. Torching your steel to whatever-ish color, saturated with garage atmosphere and quenched in used motor oil with a pad of butter will give me a whatinistic crystal structure of the correct grain size? Will the leaf springs off my Aston-Martin be austen-martensitic enough?

This topic may be better suited to a gun enthusiast or blacksmithing forum. However, if there are some methods for creating some interesting alloys using thermite that don’t result in a large portion of the product violently erupting from an old paint can an a few slaggy chunks of iron, I am all ears.
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[*] posted on 3-1-2018 at 16:57


Quote: Originally posted by unionised  
Quote: Originally posted by joseph6355  
[
Yeah, lets just rely on the government and private companies to protect ourselves.


I guess you make your own bullets, make your own powder + make your own guns too.


I have, it really isn't that hard you know.
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[*] posted on 4-1-2018 at 06:11


OP here.
I see that you guys are not willing to even consider the idea.
I'll try it somewhere else.

I will not answer anymore questions, I don't think it's worth it since people here seem to be very close-minded.




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[*] posted on 4-1-2018 at 09:55


You weren't really answering questions in the first place.

Fulmen tried to discuss the metallurgy with you and ask about your annealing procedure but you wouldn't deign to answer.

Walruslover69 actually went full walrus and asked repeatedly for information you wouldn't supply about plate sources.

Your few answers were primarily aimed at justifying your survivalist aims, not explaining the project.

Hard to see what you were expecting.

Unquestioning and universal approval?


Besides, your post reads like you culled your information about armor from PMJB, or the Poor Man's Armorer, or other sources like that as opposed to actually going to the effort to find legitimate, reliable information.









[Edited on 4-1-2018 by SWIM]




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[*] posted on 4-1-2018 at 10:07


He's a quitter, good riddance.



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