Hardening 4130 in 18 gauge?

[Ironbadger]

I've been pondering making some pieces in 4130 chrome-moly lately as an experiment.

However, I am uncertain of how exactly to harden and temper steel that thin.

I have seen both oil quench and water quench mentioned for this alloy in very thin gauges.. But I am used to oil quench for what I normally do, and leery of water quenching for what it did to some blades I made over 25 years ago.

So the question for those with actual experience is- What quench is recommended for armor in this alloy?

I am looking at this-
http://www.onlinemetals.com/merchant.cf ... &top_cat=0

There is another potential issue.
I would have to rely on torch or forge heat and judging temperature by eye, as I do not have an electric oven or thermometers to control temp precisely.

I suspect I would be courting failure before I even begin....

The alternative would be to make up parts to be hardened and tempered by someone else.
But I don't feel quite right going that route.
Call me odd, but it feels almost like I am not being honest if I rely on someone else to do that part of the job for me...Despite outside contracting being an old and honored traditional means of doing bothersome specialty work in just about every craft thats ever existed.

For the moment, it remains an idea that I am toying with for upping my skill level to making BOTN level armor....But one where I am very concerned with the safety of what I would be offering to fighters that I consider friends.

-Badger-

[Konstantin the Red]

Looks like you can use the magnet test for determining if you have attained critical temp with 4130.

Tempering it up to 450 F/233 C is readily enough accomplished in a kitchen oven. Use an oven thermometer.

[Tascius]

The material is forgiving. Use a magnet and brac parts. I use threaded rod for braces. You can buy a pyrometer for about $20. On eBay.

[Signo]

When I investigated the same matter (in a future perspective) I've discovered a thing that is called spray quenching or mist quencing with water. I thought that common garden equipment for irrigation could be enough and simple to create a spray or mist "volume" to quench thin metal into. My idea was to put a pipe with nozzles inside a barrel, and it should be good to go.
Obviously I've not yet tested this idea, but maybe is food for thought.

[Ceawlin]

You'll never know until you try...

I've been hardening 0.032", 0.040" and 0.050" (roughly 21, 19 and 18 ga.) for a few months now, using a water quench (with soap and Epsom salts added for a sort of super-quench) with good results. I've got a small one-burner propane forge for small pieces, and a kiln for larger items.

I don't have a hardness tester, so I can't confirm except by feel and stress-testing how hard my items got, but they seem as strong as when I had previous items professionally heat-treated (where they used an oil-quench).


There is a lot of scale to sand off. I've heard you can use an acid bath to take it off, but someone mentioned that the 4130 can become brittle under certain conditions.

I've successfully heat-treated small knives cut from 16 ga., knee and elbow cops, a set of 18 ga. gauntlets, all with no apparent warpage. The warpage I have gotten was mostly in the really thin 0.032", not the 18 ga. It can be reduced in the usual ways, i.e. putting things like knives into the quench blade first, or cops in vertically/edge first.

[Eachann]

Ceawlin, what are you using for your tempering (temperature, time, etc)? I was under the impression that due to the low amount of carbon (0.3 %), you really couldn't over-harden 4130 for armor (not an expert, just an interested bystander).

Ps You may want to change your location, otherwise we will disparage you for missing practice tomorrow.

[Ironbadger]

Theres something I would need to know.
I know of the trick of using vinegar to remove scale, but had not heard of 4130 possibly becoming brittle under the effects of mild acid.

Anyone have more definitive answers on this?
I'd be using something like cheap white vinegar in gallon jugs for preference because its readily available and about as inexpensive as anything I could think of, while easy to clean up.

-Badger-

There is a lot of scale to sand off. I've heard you can use an acid bath to take it off, but someone mentioned that the 4130 can become brittle under certain conditions.

[rotccapt]

I have been working with .032. I use a water quench and have been tempering to 500. For the scale I use vinegar with no noticable effects, don't have a hardness tester though.

[Ceawlin]

Ceawlin, what are you using for your tempering (temperature, time, etc)? I was under the impression that due to the low amount of carbon (0.3 %), you really couldn't over-harden 4130 for armor (not an expert, just an interested bystander)..

I've been going by the color (bright-red to orange) to best-guess that I'm above the 1600 fahrenheit critical temperature for 4130. I heat small items (like buckles or hinges) quickly in my small propane forge to bright orange, while larger items heat up over an hour or longer in the electric kiln. I use a peephole to see that it's glowing brightly before I quench.

I've also heard you really can't over-harden 4130, but I had a professionally heat-treated shield boss test out at 55 Rc, which is 5 Rc higher than should be possible. I have yet to have a piece crack or shatter yet even after repeated hammering, so while I tempered my earlier projects in the oven, I've stopped doing it recently.

[Louis de Leon]

You can do it, it's possible. I've done it.

My process is to get the pieces up to a nice orange, then quench in vegetable oil. It's super important to brace your parts when you're working with thin stuff. If you don't the piece will cool rapidly and "corkscrew" and bend as it lowers into the quench. The rapid non-uniform cooling will twist the piece.

After that, I do half an hour in my oven at 550F to soften it up a bit and normalize stress in the piece.

I've used cheap white vinegar to remove scale, worked fine for me.

You can get a truckload of vegetable oil at GFS or any other restaurant supplier.

[Tom B.]

Info in this thread is a good place to start your testing.
Hardened and Hardenable Metals Suitable for Making Armour

4130 / (EN) 25CrMo4 -
In my opinion 4130 looks to be the best material for SCA, BotN,
and ACL armour in all area except rust resistance. The heat
treating process is much more forgiving with 4130 than with
1050 carbon steel. The yield strength and ductility are better
at higher hardnesses than with 1050.

In the USA 4130 is currently easier to purchase in small amounts
than 1050. Welding filler rod is available in 4130, but not in 1050.

The as water quenched hardness for 4130 is Rc52, for 1050 it's
Rc62. The effect of this is that accidentally dropping or hitting a 4130
plate that has not been tempered is much less likely to cause it to
crack,

Tempering temperatures suitable for armour are much lower, than
with 1050 carbon steel. The effect of this is that a kitchen with good
temperature controller can be used to temper 4130 plates,

To harden 4130 heat it to 1650F to 1700F depending on how long
it take you to get it into the quench tank after you open the kiln door
and quench it in water. When tempered at 400F for 30 minutes it
seems to resist denting as well as 304 stainless steel 2.8 to 3 times
its thickness. Data sheets for 4130 stainless steel list the 2% yield
strength at that temper as 220ksi with a elongation before break of
10%. When tempered to 500F for 30 minute temper the 2% yield
strength at that temper as 208ksi with a elongation before break of
11.5%. When tempered to 600F for 30 minute temper the 2% yield
strength at that temper as 195ksi with a elongation before break of
13%.

For ACL armour other than helmets I recommend a 500F / Rc48
temper. For helmets I recommend a 600F / Rc45 temper. If you are
using an oven for tempering that only goes up to 550F, that should
be fine.

[Tom B.]

There is another potential issue.
I would have to rely on torch or forge heat and judging temperature by eye, as I do not have an electric oven or thermometers to control temp precisely.

I suspect I would be courting failure before I even begin....

-Badger-

A torch might be difficult to get a uniform temp on the piece which could lead to varying hardness across the pieces and could contribute to warping.
The forge depending on size and design would very likely be a better option.
If this is something that you decide to pursue as a more common type of work then investing in a kiln with temp monitors and/or controls.
It is pretty easy & inexpensive to add digital controls to an electric kiln.

[Ironbadger]

For the moment, its something I am looking to do to see what its like.
I'm no longer looking to become a full time armourer.
Mostly, I am doing it for myself and to make a bit of cash once in a while.

But there is a lot I would really like to make, and plenty I want to learn, just to learn it.

The idea of making lightweight, hardened armor appeals to me as a skill to learn, and maybe to profit from once in a while.

I'm never going to be competing with more dedicated armourers, as I'm more of a knife and sword making guy at heart.

But I would like to play with 4130 armor, if I can manage suitable tools.


-Badger-

If this is something that you decide to pursue as a more common type of work

[Tom B.]

For the moment, its something I am looking to do to see what its like.
I'm no longer looking to become a full time armourer.
Mostly, I am doing it for myself and to make a bit of cash once in a while.

But there is a lot I would really like to make, and plenty I want to learn, just to learn it.

The idea of making lightweight, hardened armor appeals to me as a skill to learn, and maybe to profit from once in a while.

I'm never going to be competing with more dedicated armourers, as I'm more of a knife and sword making guy at heart.

But I would like to play with 4130 armor, if I can manage suitable tools.


-Badger-

As others have said 4130 is pretty forgiving.
Small pieces obviously would be easier.
Getting up to critical temp and quenching won't be too bad.
Getting the temper right will be much more difficult.

Get some material and make a few small test coupons and figure out your process.
Destructive testing and a set of hardness files should help you get set up.

Good Luck

[Baron Alcyoneus]

Theres something I would need to know.
I know of the trick of using vinegar to remove scale, but had not heard of 4130 possibly becoming brittle under the effects of mild acid.

Anyone have more definitive answers on this?
I'd be using something like cheap white vinegar in gallon jugs for preference because its readily available and about as inexpensive as anything I could think of, while easy to clean up.

-Badger-

There is a lot of scale to sand off. I've heard you can use an acid bath to take it off, but someone mentioned that the 4130 can become brittle under certain conditions.

Unless the material already has cracks in it, I see no reason why a mild acid bath is going to cause it to become brittle.

Recently, at work, we had some thinner bar stock that had some cracks in it from the mfg before we started machining it. So, we sent it out for ultrasonic inspection, and wound up going with thicker stock hoping that it wouldn't have the same problem.

Then I determined that these parts weren't made right, and decided that they were scrap. We sell each of them (clevis fittings for Beechcraft 1900s) for about $1800. I scrapped 9 of 14.

[Tom B.]

4130 is susceptible to Hydrogen Embrittlement


"Stay away from reducing acids such as HCL or H2S04"

Paper on - Hydrogen Embrittlement

[Baron Alcyoneus]

I've baked a LOT of metals at 400F for 3-4hrs to prevent hydrogen embrittlement, typically when nickel or chrome plated.