The Armour Archive

Construction question for you guys.

I am building a 1050 Steel helm that will be heat-treated. I would like to weld perforated steel behind the eye slots to allow the helm to be used with untipped blunts.

So heres the clincher. I would like to use stainless for the perf steel because of the nightmare involved in keeping non-stainless mesh rust-free.

For those of you who know more metallurgy than I do, is that possible?

I'm pretty sure oxy or tig welding stainless to 1050 won't be a gigantic issue (though if anyone with experience in how such welds hold up to abuse wants to share I'd love to know).

What I am concerned about is what effect a heat-treatment cycle will have on the stainless perf. I believe I need to weld it onto the helm *before* the heat-treatment to avoid softening up the eye slots with the welding heat. However I am unsure of whether the heat-treatment will screw up the stainless in some way.

So, is this possible? Is there a specific alloy that needs to be used?

Anyone have any experience trying to do something like this?

Worse comes to worse I'll just home-make some 1050 perf steel and paint it as best I can, but stainless is preferred.

Thanks in advance to anyone with insight.

The problem with welding to 1050 is not softening but inadvertent hardening by auto quenching in the HAZ.

Makes me worry that you're making this sort of mis-assumption on something in a critical area!

Why not punch some holes before the heat treating, then rivet the perforated stainless in afterwords? You could flush set the rivets and they would barely be visible if done correctly.

The heat-treating cycles will make the stainless more prone to rusting unless followed by electropolishing and/or passivation.

You can weld 1050 just like you can work it hot but it a proper heat-treat will have to take it up to solution temperature (which it should anyway) before quenching.

During the heat and quench cycle the 2 materials will have different thermal shrink properties but given the open-hole pattern in the stainless I don't see it inducing any considerable stress in the 1050.

If you attempt to weld the stainless in AFTERWARDS then there will be a heat affected zone from the weld that is locally un-quenched then a band of air-quenched then a pand of over-tempered and then back to normal. If there is a worst case scenario then someplace in the rainbow pattern it will occur. The good news is that we arn't designing aerospace equipment and having a small weak section does not make a helm dangerous. Actually since it's 1050 rather then 1085 even a brittle or soft section is probably as strong as A36 'mild' steel.

Luck!
Sean

Hmmm, Thank you for that info guys. I think I'm going to go the safe route and just use 1050 perf plate coated as durably as I can manage. The eyeslots are not an area I want to be using any method that isn't 100% sound.

Thomas - I was worried as well that is why I asked here *before* building and potentially selling the helm.

Sean - I remember reading/hearing at some point that heating standard stainless alloys to critical temperatures affected their "stainless" characteristics and you have confirmed that fear. Thanks for the detailed information as always.

Jurgen- Thats also a possibility and maybe I'll throw together a test mockup to see how much abuse it can take but being that these plates are going to be directly protecting people's eyes and they may be getting hit full force with untipped blunts I just trust a full perimeter weld more than rivets.

Thanks again guys... Simplest solution looks like the best one here.

WinterTreeCrafts wrote:Jurgen- Thats also a possibility and maybe I'll throw together a test mockup to see how much abuse it can take but being that these plates are going to be directly protecting people's eyes and they may be getting hit full force with untipped blunts I just trust a full perimeter weld more than rivets.

Then set the perf outside the 1050. That way, if anything (even a weld) fails, the worst that happens is that the perf falls off, after it gets hit. If anything fails with an interior weld, that perf is headed straight into the face.

If you are really that worried about the rivets failing when you put it on the inside, then put backing strip on the back side of the perf and rivet through all three layers. Even if a rivet failed, the backing strip would transfer to the rivets on either side. Or put it on the outside instead.

Jurgen

WinterTreeCrafts wrote:Sean - I remember reading/hearing at some point that heating standard stainless alloys to critical temperatures affected their "stainless" characteristics and you have confirmed that fear. Thanks for the detailed information as always.

Welcome. The amount that the stainless will loose it's rust inhibiting properties depends a LOT on the grade of stainless and how it is heat-treated. Generally you can move stainless with a torch just fine if you use a reducing (oxygen poor) flame so it burns any extra available carbon rather then leaving soot on the surface of the stainless. It's the carbon in the soot that will merge into the stainless alloy and affect the rust resistance. Likewise if you heat and quench stainless in oil the oil can deposit carbon while water can not. The type of oil and temperature before quench play a role too. If you are heating in a propane kiln that is better then heating over a sooty carbon coal fire.

At work I do a fair amount of disimilar metal welding (different stainlesses together). I've reached the conclusion that structurally there is theoretical book learning that states there is an effect and practical experience that says the effect doesn't matter. If you have time to run an experiment you could try welding a strip of perf plate to 1050, heating to orange with a torch, quenching, drop in your oven and then throw it outside to rust, spritzing it with salt water regularly. You will likely find that even the 'compromised rust resistance' of the stainless is still superior to the rust resistance of the 1050. Add a layer of black paint inside over both metals and outside over just the SS perf plate and it's likely to be far superior for rust resistance (and plenty of strength) compared to 1050 perf plate.

Good Luck!
Sean

http://corrosion-doctors.org/Definition ... series.htm

Since the 1050 is more prone to corrosion than stainless attaching stainless to it will make the 1050 much less rust resistant. I also vote for painting the 1050 perf plate. Using stainless will result in more rust overall.

When putting any dissimalar metals together the metal that falls lower on the nobility scale should be considered sacrifical as it will take the corrosion for both metals.

Welding dissimilar metals together will cause increased corrosion at the location of the weld which will over time cause the weld to deteriorate.

When considering nobility of metals I would look at armour as being in a sea water environment due to the amount of sweat armour comes into contact with.

Welding stainless to ferrous metal isn't difficult though It can be done with mig as well. As a side note if you prefer welding with MIG you can find 1050 mig wire quite easily.

Mad Matt wrote:http://corrosion-doctors.org/Definitions/galvanic-series.htm

Since the 1050 is more prone to corrosion than stainless attaching stainless to it will make the 1050 much less rust resistant. I also vote for painting the 1050 perf plate. Using stainless will result in more rust overall.

True but it neglects the effect of surface area and volume. If you attach a LOT of high nobility metal to a small piece of low nobility metal then you have effectivly given the low nobility metal all of the surface area of the system and it sucks up the majority of the rust. This is why you attach a zinc plate (#4) to boat keels or rudders (steel ~=30) as a sacrafice to the rust monsters of the ocean.

In reverse if you attach a little of a high nobility metal to a large piece of low nobility metal then it really doesn't speed up the rusting of the big piece much at all. (steel rivets in aluminum tend to be ok, aluminum rivets in steel are gone quickly)

Guessing at the size of the stainless perfplate for the eyes, I don't think it will drasticly affect the rusting of the 1050. It will also help preserve the stainless from rusting if it picks up carbon from the heat-treating process converting it from 301SS (#39) down towards 410SS (#32)

We decorate armor with yellow brass (#46) and copper (#33) and no one shrieks in horror for all the additional rusting it causes to their steel (#30) helmet even though they are both higher on the nobility chart.

Honestly I've considered riveting in a few sacraficial zinc tabs to some of my armor to see if I couldn't help with rust prevention. There are supposed to be cold galvinizing paints/pastes that do the same thing.

Sean

Neat wasn't aware of the effect of surface area ratios. Attaching brass trim etc to mild would cause galvanic corrosion at the area of surface contact though correct? So the effect with brass trim isn't usually visible because the area of surface contact isn't visible.

Also it's true that this isn't that big of an issue with armour. Good to understand what's gonna happen though. Corrosion and deterioration of a stainles/ferrous weld isn't likely to be an issue for a good 10 years in a helmet.

This kind of stuff is more of a concern in things where you don't see the effects and failure is catastrophic such as structural steel in a building. Still good to know though.

Mad Matt wrote:Neat wasn't aware of the effect of surface area ratios. Attaching brass trim etc to mild would cause galvanic corrosion at the area of surface contact though correct? So the effect with brass trim isn't usually visible because the area of surface contact isn't visible.

Surface area and surface condition almost always affects rust. You may not get rust at the contact points of 2 metals either. Lets presume an armorer mirror polishes a helm and attaches lots of brass that is polished on both sides. Fighter decides shiny is too shiny and dulls the entire surface with lots of micro scratches from a green scrubbie. The satin finish therefore has more surface area. The surface are exposes more oxygen ions to the steel rust is esentially an electro-chemical reaction. If one area rubs against his buckle or sneck hook it might develop even deeper scratches.

When the brass is exposed to Oxygen ions then one molecule tries to rust BUT it takes an electron from the steel and instantly un-rusts. Now the steel helm is electricly charged and balances out by combining with an oxygen molecule to form rust, usually at a location where the rust can form easily. That is rarely in the air-tight highly polished area under the brass. It is far more likely on a scratched surface and/or someplace still moist from salty breath.

Attach a large enough brass 'antenna' to a helm and it will bump into all sorts of ions but it will keep sucking electrons out of the steel to stay neutral and force the steel to rust instead. Bigger antenna, faster the less noble metal rusts away.

You can also play games with keeping the metal grounded or attached to the correct pole of your car battery so there are always extra electrons to prevent the rusting. (That's why the rusty terminal of your car battery isn't the one connected to the frame.)

Not to say rusting WON'T occur at the interface. Aluminum chicago screws to hold soggy, sweat-soaked chin-straps treat the entire helm as an antenna and will rust right at the interface enough that they will adhere... but they will also rust up the threads, rust under the leather and rust on exposed surfaces too. Thankfully they can be drilled out and technicly they may have prevented a small portion of rust to the rest of the helm.

And that good readers is Mr. Wizards science lecture for today. Go make a lemon-juice battery or something.

Sean

I don't have a lemon handy, can I make an Antikythera mechanism instead?

Remember you bring the sacrifice to the altar and never the altar to the sacrifice!