Spring Steel VS. Mild Proofing Test (cool pictures)

[WinterTreeCrafts]

From the Winter Tree Crafts R&D department (which is another way of saying that I am caught up on orders)

I wasn't going to post this for another week or two, but reading the other thread about spring vs. mild steel made me want to jump the gun a bit.

So I have been experimenting with various heat treatment recipes for spring steel in order to decide which recipe would produce the best and most reliable results for production use with my armour.

After subjecting a whole bunch of test pieces to all sorts of abuse in my shop I made 4 test plates and handed them to one of my self-described "gun-nut" students (the guy has more firearms than I do hammers) with instructions to shoot them with "old guns" and to report back to me.

The results of this very unscientific test are as follows.

Hardening process: Pieces were heated to approx 1550 degrees F and immediately quenched in canola oil (vegetable oil). Anecdotaly, veggie oil seems to give a quench somewhere between that of transmission fluid and water. I have chosen to use it in my shop because the transmission fluid made the shop stink to high heaven and tastes like it would kill me slowly. The canola oil smells like french fries and doesn't smoke nearly as much.

All pieces are approx 6"x6" and were cold dished to a depth of approx 2".

Test piece A: 16 gauge cold rolled mild steel. No heat-treatment

Test piece B: .062" 1050 Steel. Hardened and then tempered at 650 degrees F for 30 minutes and then air cooled.

Test piece C: .062" 1050 steel. Hardened and then tempered at 600 degrees F for 30 minutes and then air cooled.

Test piece D: .062" 1050 steel. Hardened and then tempered at 550 degrees F for 30 minutes and then air cooled.

All 4 test pieces were shot twice at close range while braced against the wall of a sand pit.
First with a .32 caliber black powder dueling pistol.
Second with a .58 caliber Civil-war era musket firing a 200 grain round lead ball.

Exhibit A:



Surprisingly, the very low powered .32 didn't even penetrate the mild steel sample. However, as expected the musket blew a large hole clear through. Moderate deformation of the plate, steel on the rear side was very jagged and showed many tears.


Exhibit B:



The softest of the spring steel plates fared better than the mild but not as significantly as I expected. The .32 created a minor dent while the .58 musket round did achieve penetration. The steel deformed significantly and actually tore as the musket ball deflected off from its initial impact point. No cracks formed other than the tear.


Exhibit C:



Will be the recipe I use for all of my armour methinks
The plate amazingly survived both gunshots. The .32 shattered on impact with almost no deformation of the plate. The .58 musket ball massively deformed the plate but did not achieve any penetration.

Exhibit D:



The hardest of the test pieces, which I expected to perform the best actually failed rather catastrophically. While the .32 had no notable effect, the .58 ball nearly destroyed the plate. This may be due in part to the .58 ball impact being fairly off-center compared to the other test pieces. What little was left of the .58 ball did achieve some limited penetration after some deflection but the hardness of the plate resulted in multiple fractures and cracks emanating from the point of impact.
The rear of the plate is extremely sharp and jagged and overall there is also massive deformation.


These results are fairly consistent with what I acheived in my hammer-abuse tests. Pieces tempered under 600 degrees were extremely stubborn to deform but would begin to crack under repeated blows in the same spot. 600-625 degrees appears to yield IMO the best balance of strength and durability for armour applications. Please note for anyone attempting to replicate, the choice of quenching medium WILL affect the ideal tempering temperature to achieve the same balance.

Thats all for the moment from Winter Tree Craft's R&D department. I hope you all enjoy the results of our rather unscientific test

Edit: To update links

[Odd]

Do you have a problem with locals making rattan move so much they have musket level energy dump?

[Keegan Ingrassia]

Do you have a problem with armourers researching tempering methods to improve the quality of their wares, that are not directly related to SCA conditions?

[schreiber]

I'm not surprised about the .32, since I remember Halberds putting up pictures of 16g he had shot with modern guns, and IIRC 9mm Parabellum couldn't get through 16g mild.

I AM surprised about the musket ball having so much energy. Also, could you verify the types of bullets used? The dueling pistol probably was using balls, but in the War for Southern Independence, bullet-shaped bullets were commonplace. I think higher pressure pointed bullets vs. lower pressure round bullets would make a bit of a difference.

How exact was your tempering? Were you doing it in a kiln?

[losthelm]

Distructive testing is fun with a capital F.

Even when the numbers don't work out like you expect.

[WinterTreeCrafts]

While not a 100% direct correlation the way the plate handles the energy of a gunshot will reflect upon how that plate will handle 10 years of SCA or WMA abuse. Besides, my gun nut student was bouncing around in a very giddy fashion when I gave him this particular homework assignment, that alone was worth it

I also think it is interesting in a historical context given so many references to "crossbow proofing" and "pistol proofing".

My goal is to make armour that takes advantage of the benefits of spring steel while minimizing the risk of cracking so that the armour will last a LONG time. It would suck to spend $500 on an arm harness only to have the wing on the cop snap off due to repeated bending under blows.

I'll shoot it, hit it, smack it, kick it with whatever is necessary to ensure to my satisfaction that my armour will not crack into jagged sharp edges on the body of my customers.

Schreiber- In both cases the bullets were round lead balls. I can't attest to powder specifics such as type and amount but I asked my student to load the guns in a typical manner rather than get creative to beat my armour.

A new, digitally controlled kiln was used to heat the pieces for both the hardening and tempering processes. It is a large kiln so it would spike up to 15-20 degrees above target after loading due to element and controller lag but would cool back to target within 2-3 minutes. Since the pieces were just loaded and thus still absorbing heat I don't think this affected their max. temp at all.

[Sean Powell]

SWEET! Some people have advocated tempering 1050 as low as 400-450 and I felt that this was too brittle but didn't have any evidence to support it. Quenching can be done in a backyard forge for smaller stuff and 600 is an upper end of what a good oven will do. That's a very achieveable recepie for other people to duplicate. Thanks for sharing!

Sean

[Balthazar von Knopf]

Kick ass!!! Yes, destructive testing is always a good "learning experience"

Balthazar

[Halberds]

Cool post.
Thanks for the pics.

Hal

[Jeffrey Hedgecock]

Interesting test and worth doing. Thanks for the info.

Your 600-650 tempering temp seems about right. I personally don't like tempering for that long however, but that's just me.

I think perhaps your 1550 hardening temp is a little high and may have led to your cracking failure (example D). If you had gone 50-75 degrees lower and used certain types of water quenchant, you probably would not have seen the plate failure. But you were using oil, so maybe the higher temp is warranted.

What sort of lag time do you have between extraction from the kiln and quenching?

What's "close range" with the gun?

[Lorccan]

Very cool! Thanks for sharing, and supplying enough information that we can understand the limits of the test.

[Kenwrec Wulfe]

Interesting test and worth doing. Thanks for the info.

Your 600-650 tempering temp seems about right. I personally don't like tempering for that long however, but that's just me.

I think perhaps your 1550 hardening temp is a little high and may have led to your cracking failure (example D). If you had gone 50-75 degrees lower and used certain types of water quenchant, you probably would not have seen the plate failure. But you were using oil, so maybe the higher temp is warranted.

What sort of lag time do you have between extraction from the kiln and quenching?

What's "close range" with the gun?

On top of these questions, I would also be curious how exacting your temperatures were, how long you drew the temper out and what "cool down" process you used after the temper. I have found that all of these factors affect the end result.

[Aaron]

Do you have a problem with locals making rattan move so much they have musket level energy dump?

Local calibration changes from location to location.

[WinterTreeCrafts]

I think perhaps your 1550 hardening temp is a little high and may have led to your cracking failure (example D). If you had gone 50-75 degrees lower and used certain types of water quenchant, you probably would not have seen the plate failure. But you were using oil, so maybe the higher temp is warranted.

What sort of lag time do you have between extraction from the kiln and quenching?

What's "close range" with the gun?

I think the oil may require the higher temp. For my first batch I set the kiln to 1475 and after the veggie oil quench I could actually bend the pieces by hand and there was not very much spring-back. The pieces were still malleable under the hammer and so I concluded that they hadn't been fully hardened and thus jacked the temperature up. I think when I did some quenching in water I had the kiln set to 1500 and I could shatter the plates just by stepping on them afterwards.

I imagine there are too many variables in terms of the physical operation of grabbing the plate and getting it into the quench for the numbers to be super-reliable in terms of results. I'll try to get a video up to serve as a reference point.

I set the kiln to 1550 mostly because its such a big kiln by the time I get the door open and get a hold of the piece I figure the cool air has dropped the temp a little bit. I timed myself and from the instant I get a hold of the piece with the tongs to it being fully submerged in the oil is 2.5 to 3 seconds on average.

I was under the impression a 30 minute temper was standard. If its not revealing trade secrets, how long do other folks generally soak their steel?

As for range with the firearms, the dueling pistol was at about 5 yards and the musket no more than 15 yards.


Kenwerc: The kiln was brought up to tempering temperature, the pieces were placed into the kiln and then left for 30 minutes. Once the timer went off I removed the pieces from the kiln and allowed them to air cool back to room temperature.

As for how exacting, I'm not sure how to answer that. Probably about as exacting as a large digitally controlled kiln can be expected to be.

[BendSinister]

Cool!
Your test results back up the historical claims of spring steel breast plates that some soldiers privately bought during the Civil War. Those who were hit suffered from massive bruising and concussion, the plates were dented, split and some times cracked but not penetrated. As your ranges were very short, the damage was greater to the armour than at a longer range. Still the armour absorbed a lot of the force. Armour is so cool.

BS

[Kenwrec Wulfe]

I was under the impression a 30 minute temper was standard. If its not revealing trade secrets, how long do other folks generally soak their steel?

As for how exacting, I'm not sure how to answer that. Probably about as exacting as a large digitally controlled kiln can be expected to be.

Thats about what I meant for the "exacting."

I have done times between 20 minutes and 45 and have found that you really get nothing after about 30. However, I have found that allowing the pieces to cool at a slow rate (in a cooling oven) offers a better overall temper.

[WinterTreeCrafts]

Define "better"?

Softer, harder, more homogeneous, less likely to crack. What would the benefit of a slow controlled cooling be vs. an air cooling after tempering?

[Rittmeister Frye]

That's pretty cool, and consistent with a lot of historical statements as well as modern research on the subject (the Graz studies, for example). In the 16th Century, it was generally acknowledged that at much over 100 yards distance, a well armoured man was pretty well impervious to all but the heaviest of musket shot. Nice to see that you've found a good means of reproducing such quality armour plate.

Cheers!

Gordon

[Indianer]

I think perhaps your 1550 hardening temp is a little high and may have led to your cracking failure (example D). If you had gone 50-75 degrees lower and used certain types of water quenchant, you probably would not have seen the plate failure. But you were using oil, so maybe the higher temp is warranted.

For my first batch I set the kiln to 1475 and after the veggie oil quench I could actually bend the pieces by hand and there was not very much spring-back. The pieces were still malleable under the hammer and so I concluded that they hadn't been fully hardened and thus jacked the temperature up.

I set the kiln to 1550 mostly because its such a big kiln by the time I get the door open and get a hold of the piece I figure the cool air has dropped the temp a little bit. I timed myself and from the instant I get a hold of the piece with the tongs to it being fully submerged in the oil is 2.5 to 3 seconds on average.

Hello all, i have a few questions concerning this...they are simple i guess, but i wonder how to answer them myself...

1) What does such a kiln look like, that you can fire up to a certain temperature? The tempering ovens i heard of, if i remember right, cannot get so hot...or do they?
2) When grabing a larger piece like a breastplate after hardening (not tempering) - how do you grab it to submerge it, when it is so brittle? A rough grip with the tongs and it could shatter, a too large piece and it could shatter under its own weight? How is it?

Thanks for any input/correction
Best, Indi

[Vermillion]

nice job !

[Aaron]

Wow! Old post bumped up!

I was looking at this post and going "WOW!! This is totally a post I'd say something complimentary on!" And what do you know, I did in 2010!