Spring Steel Question; C75 and it's use for armor

[Jan van Nyenrode]

Hi all,

Locally I am having difficulty sourcing C60 1mm thick sheet in low volumes or at reasonable prices. Now I have been offered C75 instead of C60. What is the hivemind's opinion on this grade for armour? Anybody have any experience using this grade?

Looking forward to your replies.

Cheers,

Jan

[Craig Nadler]

Can you get C50? I'm guessing that C50 is the same as 1050 is in the USA.

[Jan van Nyenrode]

Hi Graig,

C50 would be the same as 1050 but not really available. The 'available' grades are C45, C60 and C75. Of these the C45 is only available, as far as I have found, in >3mm and the rest either asks too much money/volume or offer C75.

Just now I got a lead on some possible C55 supplier in Germany a couple hours away. Tomorrow I'll call them for pricing. Hopefully that works out, but for now C75 is the only real offer on the table.

It seems to be the common grade used for spatula's, so that would seem promising. Only thing is, it is a bit cost prohibitive to buy several sheets to experiment and then find out it is useless for armour.

Cheers,

Jan

[Craig Nadler]

I think that C75 would work for armour, but the tempering temperatures will be different.

[James Arlen Gillaspie]

If we are talking about something with 0.75% carbon, I would say no. Anything much over 0.40% just leads to greater potential hardness, which means BRITTLENESS, with no increase in toughness. The only way I would use it would be to give it a fine pearlite microstructure, which might be pretty impact resistant. I have some 1075 around; one of these days I might play with it, but the durn stuff is a pain to cold-work, and I'm lazy about hot-work (though I am theoretically a big fan ).

[Kalle Ommer]

Hi Graig,

C50 would be the same as 1050 but not really available. The 'available' grades are C45, C60 and C75. Of these the C45 is only available, as far as I have found, in >3mm and the rest either asks too much money/volume or offer C75.

Just now I got a lead on some possible C55 supplier in Germany a couple hours away. Tomorrow I'll call them for pricing. Hopefully that works out, but for now C75 is the only real offer on the table.

It seems to be the common grade used for spatula's, so that would seem promising. Only thing is, it is a bit cost prohibitive to buy several sheets to experiment and then find out it is useless for armour.

Cheers,

Jan

Hallo Jan

I do have the same problem. The vendor where I normaly by steel wants 325 Euro´s for a sheet (2x1 m) of 1mm C45. If you find a cheap source for spring steel, I would be glad if you told me where. Maybe if we both get one or two sheets the price would even be less....



Greetings

[wcallen]

I use 1050, I like 1050.

I do know of armour that has been made from 1070 and it seemed to work out well enough. So it has been done. I expect you need to be very careful in hot work, cool down from hot work and the hardening and tempering processes to be sure you don't end up with something that will crack or shatter.

So it can be done, but I am not sure I would want to.

Wade

[schreiber]

So, did anyone else misread "CZ75" and assume there was some Halberds-style destructive testing going on?

[Caius705]

So, did anyone else misread "CZ75" and assume there was some Halberds-style destructive testing going on?

Came for that, stayed for the spring steel.

[Kristoffer]

You could try finding 25CrMoS4 as an alternative. I have been able to find it available from airplane part suppliers as it seems to be the steel of choice for constructing airplanes.

[Aussie Yeoman]

I just had a quick look in Machinery's Handbook.

Even when dead soft annealed, 1080 steel is still 150% stronger than work hardened mild.

So it could be that you could make armour from 1075 cold, and still be much stronger than mild. Or, heat and quench, and then bring almost back to soft but not quite so, and be very much stronger than mild.

That being said, I have zero personal experience heat treating steel.

[Jan van Nyenrode]

Hi everybody,

Thank you all for your comments. For now I'll wait a few more days on the reply from the german source. They have C55s annealed 1mm thick and 1,2 mm thick on stock so that is positive. Only the price will now be the issue.

Kalle Ommer, I've send you a PM.

With kind regards,

Jan van Nyenrode

[Bender]

Is there a spring that's good in an oil quench?-aka-no need to temper after the fact?

[wcallen]

I just had a quick look in Machinery's Handbook.

Even when dead soft annealed, 1080 steel is still 150% stronger than work hardened mild.

So it could be that you could make armour from 1075 cold, and still be much stronger than mild. Or, heat and quench, and then bring almost back to soft but not quite so, and be very much stronger than mild.

That being said, I have zero personal experience heat treating steel.

We did some unhardened/untempered 1070 armour from something we called 21g. I don't remember how thick it was exactly. It certainly dented, but it was light and way better armour than 21g mild would have ever been. The pieces that were just curled dented a good deal. The cop we raised from the stuff was still pretty sound after several years. It woudl have been more "normalized" after what we did to it and then planished.

Wade

[Jan van Nyenrode]

Hi all,

Just wanted to thank you all, and let you know I have found a source for 4130. Apparently Aircraft Spruce has a european affiliation in Germany. By pure chance (I was searching for a Roper Junior nr. 5 benchmount in Europe) I checked their metals department and found 4130 sheet.

it's a bit expensive at circa 10€ the kg, but the fact that you can order very small quantities in relevant thicknesses makes up for that.

www.aircraftspruce.eu

Just got confirmation, coming Thursday I'll have it in my grubby little hands

Cheers,

Jan

[Kristoffer]

See, I told you so

[Atlanta Armory]

I just had a quick look in Machinery's Handbook.

Even when dead soft annealed, 1080 steel is still 150% stronger than work hardened mild.

So it could be that you could make armour from 1075 cold, and still be much stronger than mild. Or, heat and quench, and then bring almost back to soft but not quite so, and be very much stronger than mild.

That being said, I have zero personal experience heat treating steel.

Unfortunately, strength isn't the only consideration. Once a material is strong enough to not dent, toughness becomes far more important. There are ceramics that are far stronger than steel, but wouldn't be worth a darn in impact; strong, but not as tough.

Toughness in this case is yield_strength*yield_strain^2 / 2. Think of the material as being a spring. The more energy it can absorb, the better.

This is why ballistic vests are generally made from Kevlar and other aramids, not carbon fiber, which is stronger and stiffer. A carbon sheet can take a lot of stress but it can't absorb energy very well since it doesn't deform much. Spider silk is not being used yet for the opposite reason. It is far better than kevlar at absorbing energy but will deform so much the bullet (and the vest with it) will be half way through your abdomen before the round is stopped. Slight exaggeration, but you get the point.

Long story short, hard and strong steels might not be superior to medium grade, softer steels for armor applications.

-Ben