Bracing for heat treatment

[Ceawlin]

Here's my latest attempt to brace a set of 4130 mid-carbon steel legs to set them in place for professional heat treatment. The cops are .050", the rest is 0.032" thick. The bracing is made of 18 ga. stainless steel.

Last time I heat treated a set of leg armor, I had some warpage... not so much I couldn't fix it, but enough it was painful, so I'm hoping this will prevent problems this time around.

Any suggestions for improvement, or have I committed overkill this time around? Should I be concerned that using sheet pieces to brace may cause problems with the quench by reducing access to some surface area? I'm shooting for Rockwell HC 45-50, or as hard as 4130 can get.

[Baron Alcyoneus]

My hunch is that those should work fine. They're thicker than the other material, so stronger (at least until the quench). I might think about putting a bend in the edges, to make them more rigid.

[Ceawlin]

Are there that few of us using heat-treatable steels that there's little interest in this?

I was very surprised the first time I had 4130 heat-treated professionally, when the rolls I felt would suffer the least warpage, turned out to have the most severe problems. I'm glad that even fully-hard 4130 can still be moved with the aid of a heavy hammer... albeit it was a 5-lb rawhide mallet, but I WAS able to shift it around again.

[wcallen]

I tend to deal with heat treating the easy way - I don't do it. 1050 even in its worked state is a lot better than mild, and I am not generally getting a lot of abuse.

Tom has done a lot of heat treating. He seems to go for even more bracing. He uses actual bar stock (even thicker) and I think he usually has some cross bracing so the thing can't go wonkey end to end.

Any bracing seems to be better than none.

Wade

[Ceawlin]

Wade, I guess I get that...

...but for actual use, you don't get the most strength for the least weight unless you heat treat.

Being a perfectionist, I guess I'm driven to keep improving. It bugs me now to build anything in mild steel where durability will be an issue.

[Gaston de Clermont]

I reckon your braces will help, though they won't do much good against a lengthwise twist, which is hard to get out. I address warping by heat treating the thing myself. If I do warp it, I can fix it hot or anneal it and fix it cold.

Shooting for as hard as 4130 will get will give you a piece that's more brittle than I prefer. You can temper it yourself if you'd like though.

[Mac]

Wade, I guess I get that...

...but for actual use, you don't get the most strength for the least weight unless you heat treat.

Being a perfectionist, I guess I'm driven to keep improving. It bugs me now to build anything in mild steel where durability will be an issue.

A tempered matrinsitic structure will be tougher than a perlitic structure of the same hardness. So, strictly speaking, it's better to go the whole route by hardening an tempering.

The question is, when is good enough good enough? The advantages of the tempered martinsitic structure come with extra costs and risks attached. The perlitic structure is easy to achieve with very low risk, while at the same time offering much better hardness than can be had from mild steel.

Each must decide for himself where to draw the lines.

Mac

[Mac]

If I do warp it, I can fix it hot or anneal it and fix it cold.

I'm glad that even fully-hard 4130 can still be moved with the aid of a heavy hammer... albeit it was a 5-lb rawhide mallet, but I WAS able to shift it around again.

As I see it, there are basically two ways to fix something that warped or twisted in the heat treating.....

--The first is by forcing it back into shape with mild heating. If the steel is stressed while in the tempering temperature range it will move and take a new permanent shape. This fix works best for things that are twisted. You must find some way to clamp the armor so that you can twist it back to the shape you need while applying heat with a torch. You will be able to feel it yield and you can periodically let go and see how you are doing. For best results, you need to keep the torch moving so as to heat everything nice an evenly. Take care not to get anything hotter than your final tempering temperature (as judged by color).

--The second way is under the hammer. If a cannon or lame has "curled up" in the heat treating, you should "plannish" it from the outside over a suitable stake. This will make it "open out". On the other hand, if it has "opened out" in the heat treating, you should "plannish" it from the inside with a suitably shaped hammer. This will make it "curl up". The work must be tempered far enough that there is no risk of cracking, but not so far that the individual "plannishing" blows leave real dents. The place where this really comes into its own is in things like greaves, where one place might curl in and another open up. It's just a question of applying the appropriate correction to the particular region.

As an aside... Grinding with a wheel that is out of true will cause a cannon to open out. This is because the grinding wheel is delivering blows to the outside. I keep my wheels very true and run them at low enough speeds that the work stays is contact with the wheel. Grinding should "hiss" rather than "howl".

Mac

[WendallVonDerEisenstein]

I have a 50lb box of 3/16" or 5/32" rod that use to brace parts for heat treating.

[Ceawlin]

I've only had three batches of items professionally heat treated so far, which included a set of 1050 mitten gauntlets, and in 4130 a set of similar gauntlets, a buckler shield, a shield boss, and a set of articulated legs similar to those above. I had a friend have 4130 plates for an early brigandine/late coat of plates hardened at the same place.

Having them all hardened to between 45-50 Rc, I have yet to have any piece shatter or crack. Several have dents or slight misshaping from SCA combat (I have yet to see the CoP, but it was for BoTN, and seems to have faired very well).

I'm waiting with high expectations that this batch will come back, and continue to prove successful in SCA use.

I am unaware of the exact process the shop I pay uses. Myself, I have an O/A torch and a single burner propane Eric Thing style sheet metal 'forge'. Since it is so small, I haven't tried to heat treat anything myself yet.

I will admit I have much to learn about heat treatment. However, my understanding of 4130 was that it couldn't get hard enough to shatter. Is that not true?

[Ceawlin]

The bracing seems to have worked very well. My work wasn't perfect to begin with, but it's virtually the same shape as before hardening/tempering.

[Gaston de Clermont]

I've never seen 4130 shatter, but I have seen it crack when it's abused in a very hard, untempered state.