The Armour Archive

Who has used hardened 17-7Ph for armour? What sort of results did you get?

http://www.atimetals.com/Documents/ati_17-7_tds_en.pdf

I use 17-4PH frequently for medical devices. It makes a decent hammer head, chisel body, driving cap or anything that needs to take an impact. It is very tough but not very hard. It does have a fairly low yield point so expect denting. 17-7 will be similar but by the numbers I don't think either would be as good as 410.

The biggest thing to remember is that the PH is for precipitation hardening. You "age" the 17-X series like you do alluminum. 4-5 hours at 950-1000C is our general standard depending on the properties we want. It's not a quench and temper type steel.

Good luck!
Sean

Sean Powell:

What heat treatment conditions have you used for 17-7Ph Stainless? I'm looking at the specs for TH1050, RH950, and CH900.

The manufacturers (AK Steel) spec sheet says that the 2% yield strength for:

17-7Ph Stainless in condition TH1050 is 185 ksi
17-7Ph Stainless in condition RH950 is 220 ksi
17-7Ph Stainless in condition CH900 is 260 ksi

The manufacturers (AK Steel) spec sheet says that the ultimate tensile strength for:

17-7Ph Stainless in condition TH1050 is 200 ksi
17-7Ph Stainless in condition RH950 is 235 ksi
17-7Ph Stainless in condition CH900 is 265 ksi

http://www.aksteel.com/pdf/markets_prod ... _Sheet.pdf
http://www.aksteel.com/pdf/markets_prod ... lletin.pdf
http://www.aksteel.com/pdf/markets_prod ... _Sheet.pdf

I just got a pile of this, and will be playng with it ... I'll let you know how it goes.

It is obscenely tough in annealed condition.

Scott Martin

Scott Martin:

Do you mean that it is "tough" to shape or something else?

130kpsi in the annealed state.

The metal that I would be buying is milled by AK Steel. Their data bulletin lists 40 Ksi as the 2% yield strength. 130 Ksi is the the tensile / breaking strength. Yield strength is the one that tells you how much force is needed to form the metal.

http://www.aksteel.com/pdf/markets_prod ... lletin.pdf

Craig Nadler wrote:Sean Powell:

What heat treatment conditions have you used for 17-7Ph Stainless? I'm looking at the specs for TH1050, RH950, and CH900.

Well, Like i said, 17-4 not 17-7 but I'll pull what I can. As I understand it 17-4 doesn't come in sheet and we work mostly in bar anyway. I'll send my work address a reminder e-mail and post what I've got on Monday.

Sean

Significantly more difficult to move than 304, 316 or 430. a bit harder to move than the piece of 410 I was playing with at the hammer-in. Quite similar to 1050 at the point where you think "I should hit this with some heat because it isn't moving any more"

Note that this was with a piece fully annealed, so I anticipate that it will be very nice when heat treated, but it isn't a nice material to work pre-heat treat, unlike 1050. That said, I live on the wet coast, where non-rusty metal is a good idea and 410 apparently has corrosion issues when treated at the cooler end of its heat treat range.

Scott Martin

17-4 comes in sheet. I picked some up from here:

http://www.onlinemetals.com/merchant.cf ... &top_cat=1

It is very springy. I was using it for gauntlet fingers as an experiment. It is insanely expensive.

Jurgen:

For a 12"x36" sheet of 17-4ph to try it out McMaster-Carr http://www.mcmaster.com is a lot cheaper at $85.71 instead of $134.11. If you are buying more than that, then United Performance Metals http://www.upmet.com/ is $368.70 for three 36"x48" sheets of 22ga. 17-4ph. Please note that the on-line prices seem to be higher than if you call United Performance Metals and order over the phone.

I just ordered a 0.031"x12"x36" sheet of 17-4ph to test it out. Even though shaping it sounds like it will be a pain I think 22ga 17-4ph will work great for COP plates, brig plates, and splints. Annealed 17-4ph stainless steel has about the same yield strength as full hard 301 stainless steel. I've already used 22ga. full hard 301 stainless steel for splinted legs so I don't think shaping 22ga. 17-4ph stainless steel will be a big problem. After it's been hardened at 925F for 4 hours it should be at least as dent resistance as 1050 spring steel at a 600F temper.

The changed the title of the thread to include 17-4Ph stainless steel in addition to 17-7Ph stainless steel. I received the 0.031"x12"x36" test sheet of 17-4ph stainless steel and will report back my initial findings later tonight. So far annealed 22ga. 17-4ph stainless steel seems to me to be harder to shape then 22ga. full hard 301 stainless steel. I cut out and shaped a COP plate. It's in the kiln now at 900F for 1 hour which should result it a heat treatment condition H900.

It seemed to me that it was easier to shape 17-4ph stainless steel after it was heat treated than before it was heat treated. This corresponds with what I read in the data sheets for 17-4ph stainless steel. According to the data sheet heat treating to a H900 condition increases the yield strength and hardness, but also increases ductility.

It seemed to me that it would work for parts that only need a gradual simple curve or a slight compound curve. It may be a good replacement for full hard 301 stainless steel for COP plates, brigandine plates, and splints. The 2% yield strength of full hard 301 stainless steel is 140ksi, for 17-4ph stainless steel in the H900 condition the 2% yield strength is 200ksi.

I'm planning on buying a few 3'x4' sheets of 22ga. 17-7ph stainless steel to try it out. Going by the data sheet annealed 17-7ph stainless steel has a 2% yield strength of 40ksi, so it should cold form as well as mild steel.

For ACL/Botn armour my currently thoughts are that 17-4ph stainless steel may be the way to way for COP plates, brigandine plates, and splints. For other parts except for maybe the helmet 17-7ph stainless steel may be the way to go. According to the data sheet 17-7ph stainless steel is difficult to weld. For helmets that require welding you may still need to use 410 stainless steel or 304 stainless steel.

One of the nice things about heat treating 17-4 is that it doesn't get nasty fire scale on it in kilns that don't have control atmospheres. The temperature isn't high enough.

(17-4Ph Stainless Steel)


It seemed to me that 17-4ph stainless steel at a H900 heat treatment resisted denting at least as well as 1050 spring steel at a 650F temper.

The 17-7PH that I'm using is annealed and is significantly harder to move than stainless steel - from "feel" it's 2-4 gauges "stiffer" than the equivalent stainless steel, so it's significantly harder to move than mild steel, even in itws annealed condition.

Heat forming is a bit tricky as well, since a hair past orange heat it "bubbled", so if you are using heat take more care than if you were laying with stainless (or mild) since something (the aluminum?) in the alloy volatalizes at a lowish temperature. I think that I will try a set of milanese gauntlets, since the 1025 treatment should provide fairly insane toughness for nominal weight.

If this proves out I'll have to see if fluting can be done cold without mangling my tools, and look at 20-22 Ga fluted gauntlets that are in the right weight range for the period originals, and a bit tougher than with period materials.

Scott Martin

Rolling the inside corner on my pauldrons really sucked. The 16g did NOT want to shrink. The plate also wants to return to its flat state, since it hasn't been treated yet. The shop that does our stuff (they heat treat aircraft parts) said that TH1050 was optimal for our use. "If it breaks, I'm out of business" was the defining parameter for how we wanted stuff treated.

(17-7Ph Stainless Steel)

I called Bodycote today and asked what the minimum lot charge was for heat treating 17-7Ph stainless steel to the RH950 condition. Please note that the RH950 process involves 8 hours of -100F cold treatment. The ballpark price was in the $500-$600 range. The TH1050 condition is something that I can do on my own, but I'm not going to deal with the large tub of dry ice and acetone needed for RH950.

(17-7Ph Stainless Steel)


I just ordered three 20ga./0.035"x36"x40" sheets of 17-7ph stainless steel in condition A from United Performance Metals for $297.

http://www.upmet.com/products/stainless-steel/17-7ph

(17-4Ph Stainless Steel)


My initial thoughts are that 17-4ph stainless steel 0.040"/19ga/1.0mm would make some very rugged ACL/BotN COP plates and splints. The 0.031"/22ga/0.8mm plates that I tested would be good for tournaments, but a little light for bugurts. 17-4ph stainless steel heat treated to H900 is super springy. It would make far better spring pins than full hard 301 stainless steel.

(17-4Ph Stainless Steel)


I was comparing a 14ga. 304 stainless steel test plate and a 22ga. 17-4ph stainless steel test plate. I could touch the ends of a 12" 17-4ph stainless steel test plate together and after I released the pressure the plate had only slightly bent. Less pressure applied to the 14ga. 304 stainless steel plate would put more of a bend in the plate.

The point that I really should make is that there is more to selecting the plate thickness than just dent resistance. IMO, plates made from 22ga./0.031" 17-4ph or full hard 301 stainless steel are too flexible for ACL/BotN bugurt / group combat. It doesn't help you if the plate is undamaged, but you have broken ribs.

(17-7Ph Stainless Steel)

Does anyone know of a source for small quantities of 17-7ph stainless steel in mill condition C?

The only place that I found so far is Precision Steel Warehouse and they have a 100 pound minimum order at $13.75 per pound plus shipping. So it would cost me around $1500 to try the stuff out to see if 22ga. 17-7ph stainless steel in condition CH900 will work for COP plates and splints.

Please note that if someone is selling 17-7Ph stainless steel in condition C they will definitely say so. The vast majority of 17-7ph stainless steel sold is in mill condition A.


(General Comment)


FYI, the yield strength and elongation at the point of failure of these materials are as follows:

Full Hard 301 Stainless Steel_____________________140 ksi / 9%
410 Stainless Steel tempered to 400F_____________*156 ksi / *12%
17-7ph Stainless Steel in Condition TH1050_________185 ksi / 9%
17-4ph Stainless Steel in Condition H900___________200 ksi / 7%
17-7ph Stainless Steel in Condition RH950__________220 ksi / 6%
17-7ph Stainless Steel in Condition CH900__________260 ksi / 2%

* All the numbers are from AK Steel data bulletins expect for 410 stainless steel. I had to look at other sources cause AK Steel didn't list the numbers for a 400F temper.

Craig Nadler wrote:The point that I really should make is that there is more to selecting the plate thickness than just dent resistance. IMO, plates made from 22ga./0.031" 17-4ph or full hard 301 stainless steel are too flexible for ACL/BotN bugurt / group combat. It doesn't help you if the plate is undamaged, but you have broken ribs.

I have tried to make that point on numerous occasions. There are very few people who understand it.

Sean

(17-7ph stainless steel)

I just heat treated two 0.035"/20ga./0.9mm 17-7ph stainless steel test plates to condition TH1050. The heat treating process was to heat the test pieces to 1400F for 90 minutes, then air cool them for a few minutes before putting them in a 55F water tank. I used ice and a digital thermometer to keep the temperature between 53F and 57F for 30 minutes. I then heated the test pieces to 1050F for 90 minutes, then let them air cool. Here are my notes so far:

1) The annealed / condition A 17-7Ph stainless steel cuts much more crisply than annealed 410 stainless steel, which is very gummy when sheared.

2) Annealed / condition A 17-7ph stainless steel seems to cold work very well.

3) The test pieces discolored from the heat treatment, but there was no fire scale as with 1050 spring steel or 410 stainless steel.

4) My initial feeling is that the dent resistance is on par with 1050 spring steel with a 650F temper. This is based on hitting it with a 24oz.ball peen hammer. I was just heat treating 1050 spring steel to a 650F temper today so it was fresh in my mind from having to fix some minor warping. I'm guessing that the dent resistance was on par with between a 0.090"/13ga./2.3mm or 0.0109"/12ga./2.8mm 304 stainless steel.

5) It did not seem brittle. I clamped the corner of a dished plate in a vise and bent it back and forth a few times and it did not crack.



(General)

My initial findings give me hope that 17-7ph stainless steel will out perform 410 stainless steel in most areas and be the next tier beyond 410 stainless steel for high perform steel fighting armour. It also looks very much like 17-4ph stainless steel is the next tier after full hard 301 stainless steel. The cost for both 17-7ph and 17-4ph stainless steel are all most twice that of 410 or full hard 301 stainless steel.

Another thought that I had was that seeing how well 17-7ph stainless steel worked I'm thinking that I'd use it for the COP plates and splints that I was thinking for using 17-4ph stainless steel for.

I'm posting this here for posterity - I'd be interested in learning more about this as folks get experience using these materials:

I asked:

Adamo wrote:Mr. Nadler,

I didn't want to start a long thread about this, but I wanted to get your opinion on the use of 17-4ph stainless vs. more traditional stainless steels, like 304.

17-4ph H 900 has a yield strength (YS) of roughly 200 ksi, and an ultimate tensile strength (UTS) of about 210 ksi. 304 has a YS of "only" 42 ksi and a UTS of 90 ksi. I haven't looked closely at the toughness of these two materials, but it would seem that you have far less margin to failure with 17-4ph than you would with 304 SS. 301 SS seems to split the difference between these two materials. Was this something you considered when you selected 17-4ph as a material for combat armor?

FYI, all of these values were pulled from material sheets hosted by AK Steel.

I'm not looking to cause trouble, this is a topic that I am genuinely interested in.

Thank you,
Adam

Mr. Nadler replied:

Craig Nadler wrote: Please feel free to post this in the "17-4 Ph and 17-7 Ph Stainless Steel for Armour" thread: viewtopic.php?f=1&t=161122 .

I just clamped one of my 0.031"/22ga/0.8mm 17-4ph stainless steel test plates heat treated to a H900 in a vise and bent it forward to a sharp 90 degree angle, then bent it 180 degrees backwards to a shape 90 degree angle, then 180 degrees forwards. At that point it cracked. Based in that I would said that it is not very brittle. You might want to look at the elongation before break percentage to give you an idea of brittleness.

I tested 17-4ph stainless steel before testing 17-7ph stainless steel. Based in what I'm seeing with 17-7ph stainless steel I'm not sure that I'd bother with 17-4ph stainless steel. 17-7ph Stainless Steel at a TH1050 heat treatment condition seems like the best high perform steel fighting armour material that I've tested so far.

When I get the chance I may look into Charpy Test data or fracture test data for these materials - my concern is that if the material is cycled elastically (which will happen since you're shooting for the thinnest material you can get away with) you could end up with premature failures in select materials. I don't know that it would be a health/safety concern, but it could be a longevity of investment concern.

Adam

Hi Adam

premature failure due to fracture is definitely a concern, and tends to be an isue for folks who are cold-working since fatigue and cycle cracking are a major issue. I'm happier when I have a fair amount of "play" between my yield strength and my UTS, but there is a tradeoff between the "percentage" yield and the absolute difference. I doubt that anyone will use the H900 temper, since the difference between the two is less than 5% (relative) and less than 10 ksi (absolute)

My "eyeball" for the hardness that I would try first would be the 1050 or the 1025 - from the Sean Powell's post above

H1025 Lower hardness but 2.5 X impact strength

and I woud be looking for something with ~25% or so delta between the yield and failure strengths.

For a concrete example, many people use 16 Ga 304 for knee cops. This material has a yield of 42 ksi and an ultimate strength of 90 ksi. To get the same "ultimate" strength using the 17-7 with a 1050 temper (with a yield of 200 ksi) we would need to use 1/5 the thickness. I don't think that anyone is going to use material this thin. In actual practice, I would anticipate that the high performance folks would go to 1/2 the thickness, and most of us would be looking at thicker material.

At 1/2 the thickness, the choice is to go for "hard" at which point the yield strength would be roughly equal to the ultimate tensile of the 304 (185 * 1/2 / 90 = 1.0) and more than twice the yield strength (185 * 0.5 / 42 = 2.2) and roughly 2.5x the ultimate tensile strength.

Since the temper can be "tailored" to a sigificant extent some armourers may target a specific tensile / yield combination - something in the range of UTS 160 and yield 90 would allow for a "gap" of 35 ksi at half the thickness, an ultimate tensile strength slightly lower than the full thickness 304 stainless and a yield strength slightly higher than for the stainless. Obviously using 2/3 thickness will put all of the characteristics above the full thickness stainless in ultimate strength, yield strength and the energy delta between yield and failure.

Stress fractures will be a concern for these armours, but they are also a concern for stainless armour (a crack can drop the yield and ultimate strengths by 50%) but even "cracked" these materials exceed the characteristics of mild steel at "Minimum" SCA thickness.

The trade-off is in the complexity of the process, the extra time and the cost of the materials and equipment - Dr Williams notes in "The Knight and the Blast Furnace" that despite having tecnically better armour in the 15th century, the Germans lost out to the Italians because the Italians produced less expensive armour.

Carbon steel armour is likely to remain a "fringe" material in the SCA, but for "performance" applications (Jousting, BoTN, rebated steel) the cost and time trade-off is well worth it for those who participate. And there are armour nerds who want to try and make "the real thing" regardless of whether there is a market or not.

Scott Martin

Scott Martin wrote: For a concrete example, many people use 16 Ga 304 for knee cops. This material has a yield of 42 ksi and an ultimate strength of 90 ksi. To get the same "ultimate" strength using the 17-7 with a 1050 temper (with a yield of 200 ksi) we would need to use 1/5 the thickness. I don't think that anyone is going to use material this thin. In actual practice, I would anticipate that the high performance folks would go to 1/2 the thickness, and most of us would be looking at thicker material.

Scott Martin

1/5 the thickness would be true in pure tension like building a metal chain. Most armor 'fails' by denting which is essentially bending. Bending stress for a bar (like a splint) = M*c/I. c is half the metal thickness and I is proportional to thickness cubed. That means we are talking about an inverse square law. For equivalent dent resistance the bending moments at yield would be equal so:

0.059"^2 * 42ksi = T^2 * 200ksi

T^2 = .059"^2 * 42/200

T = .027" Not .012"

22 ga is .029 so a 22ga 17-7 with a 1050 temper on lamellar or a CoP would be half the weight and as dent resistant as a 16ga set of 304…

BUT as Craig pointed out elsewhere, that doesn't mean it's as stiff. Modulus of elasticity is generally very similar through all the steels so you might have armor that flexes inward, cracks a rib and pops back out with no damage to the armor but you not protected. (304 28,000-29,000 ksi Elasticity compared to 29,600 ksi for 17-7 at 1050) You should only thin your metal where the stiffness is not a concern or the shape gives more stiffness then material thickness (like a medial ridge on lamellar plates). You could make a FANTASTIC suit of fluted gothic in 17-7 that would be just as strong and half the weight because the flutes give the armor strength… but it's not a magic material that makes all armor into wonder material. You can't take the old rules and apply them with too broad of a brush just because of a little math (and I do strongly favor the math).

Good luck!
Sean

Sean Powell wrote:<SNIP>
...You should only thin your metal where the stiffness is not a concern or the shape gives more stiffness then material thickness (like a medial ridge on lamellar plates). You could make a FANTASTIC suit of fluted gothic in 17-7 that would be just as strong and half the weight because the flutes give the armor strength… but it's not a magic material that makes all armor into wonder material. You can't take the old rules and apply them with too broad of a brush just because of a little math (and I do strongly favor the math).

And this is one of the best "nutshell" explanations of the science behind the 15th century Gothic vs Milanese armours, and lets you argue another chicken and egg question: did the German armourers start fluting to increase the rigidity of their armours because they were using better materials, or did they start using better materials because their armour technique imparted the rigidity and ALLOWED them to use better (and thinner) materials.

There is lots of evidence that the Italian armours didn't heat treat their materials, and without the "stiffening" that was imparted by lots of flutes. Better materials didn't correspond to lower weight for similar protection, because of the elasticity issue, and if you need to use thicker material any way, why heat treat if it is already "good enough"?

I found it funny that my "rule of thumb" of 50% thickness was pretty close to your calculated value. It's probably also worth noting that I tend towards gothic, so my armour has less of a rigidity issue than (for example) the 14th century mafia gear I also tend toward making armour in "reproduction" thicknesses, so I think that 0.020" (thickness of the A254 plates) fluted heat treated mitten plates will perform much better than 16 Ga mild steel- and the structure has a ridge line every ~3/8" or so - there is very little flex in a 3/8" x 3/4" piece of material.

Sean, do you have any suggestions on good material science primers? I'm sure that I am not the only one who needs to broaden my knowledge base!

Scott Martin

Scott Martin wrote:Sean, do you have any suggestions on good material science primers? I'm sure that I am not the only one who needs to broaden my knowledge base!

Scott Martin

If I had one I'd be reading it. I could use one myself. Wander over to any college at the end of the semester when students are selling their text-books. Bring a case of beer. Look for the nerdy kids with worn out books and lots of hilighting.

Physics 101
"Introduction to Material Science" by Beer and Johnson comes to mind.
Any college coursebooks on statics and dynamics. I can't remember the authors I had.
Marks Standard Handbook of Mechanical Engineering or Machinery's Handbook if you want expensive general sources.

Honestly this is all clasical Newtonian physics but there is no good 'basic' primer that I know of because the only people who study the basics do so for more advanced work. Most people are just happy there is no trafic on the bridge and don't want to think about what holds it up.

Luck!
Sean

J E Gordon has some nice books understandable by human beings:
Structures - "Why things don't fall down" and Ne Science of Strong Materials - "Why things don't fall through the floor" but I don't remember either of these covering flexion or elastic loading, although it has been a while since I read them...
http://www.amazon.ca/Structures-Things- ... 0306812835
http://www.amazon.co.uk/New-Science-Str ... 0140135979

Scott Martin

Scott Martin wrote:Hi Adam

...

Carbon steel armour is likely to remain a "fringe" material in the SCA, but for "performance" applications (Jousting, BoTN, rebated steel) the cost and time trade-off is well worth it for those who participate. And there are armour nerds who want to try and make "the real thing" regardless of whether there is a market or not.

Scott Martin

I agree with you, mostly. My concern is that early adopters could be unpleasantly surprised if their $1000+ set of leg armor fails after one or two seasons of use, since their reference point would be mild steel or 304 stainless armor that can be used in the SCA for 15 years without catastrophically failing. I'm not saying that these new materials will fail prematurely, but rather that we are using a new (to us) material in a tougher environment, and it may not work out as well as we hope it will.

Scott Martin wrote:
...

Sean, do you have any suggestions on good material science primers? I'm sure that I am not the only one who needs to broaden my knowledge base!

Scott Martin

You didn't ask me, but "Material Science and Engineering, an Introduction" by Callister is easy to understand, if you're looking for a primer.

Adam

I just finished shaping and polishing an early 15th century right pauldron shoulder cop from annealed 0.035"/20ga/0.9mm 17-7ph stainless steel. I'm now in agreement with Scott Martin's assessment of annealed 17-7ph stainless steel being 2 to 4 gauges stiffer than 304 stainless steel. I polished this plate so that I can see how much rework it will need after the heat treating. My hope is that a quick buffering with a high polish buffing compound is all that is needed to remove the discoloring from the heat treating.

Great Information Guys !

Thanks for sharing. I've always wondered about the precipitation hardened stainless series, but the cost and availability has kept me from experimenting.