Heat Treating HC Spikes (1040)

[m_brothers]

Well since I am getting the hang of bladesmithing down by using spike knives, various kinds. But I make sure they are all stamped with HC. Tested them all as well. Approx: 1040 I'm guessing. I have 5 different sorts of knives and one small seax.

Steps so far...

1- Hot Forging
2- Ground and filed.
3- Annealed
4- Hardened
5- Normalized
6- Normalized
7- Annealed
8- Hardened

I am now at the last ten steps for me so far.
I need to
9- Heat Treat
10- Polishing

I need to know what temperature I should I temper it too? I'm going to do about 535F, unless told otherwise.

Yes I know, it's not real blade steel, but I want to make the knives as strong/sharp as possible. So is 535F good for a tempering temp???

Best Regards,
John

[TarAlderion]

John,

Most HC railroad spikes only sit around .3% carbon.

As far as you heat treat steps go, it is unnecessary to harden the blade, then re-anneal, then re-normailze, then re-harden. You won't really be gaining anything from that except extra practice . When making a blade, after you finish your rough forging, normalize the blade one or two times, then anneal it. You want to anneal it to make it easier to work as you grind and file it. After you finish with the rough grind, then normalize the blade. I usually do about 3 normalization cycles. You will probably want to do at least 2, 3 for good measure, and anything after that probably won't make much of a difference. After the last normalization cycle, there is no need to anneal, just go for your final heat and then hardening quench. With the HC railroad spikes, in order to gain maximum hardness use the fastest quench you can, cold water will give you some hardness, but a brine quench will give you a little more. It still won't be up there with a good high carbon steel, but every little bit counts. Following the hardening quench that is when you temper the blade. 535 F is far too hot for a tempering temperature for such a low carbon steel and is really too hot for most blades and steels. Tempering temperatures vary depending on steel of course, blade length, blade uses, and hardening methods. For example, a sword must be tempered to a higher temperature than a small knife, this is becuase the sword will see greater stress than the knife and must therefore be softer than the knife in order to absorb the additional stresses. If you differentially heat treat a blade (harden only the edge) you may not have to temper at all. For a through hardened spike knife like you have made, you will not have to temper very much due to the lower carbon content, since the blade will not be as hard to begin with, you will not have to reduce the hardness as much inorder to impart the necessary toughness. I would say that about 300F would be about as high as you would want to go. You can always start lower and work your way up. Something you can try is what is known as an edge flex test. Sharpen the blade, then take a brass rod, clamp it in a vice and place the edge on the rod. Apply pressure on the edge to try and flex it, if the edge folds, you know that you tempered too much, if the edge chips, you know that the blade needs to be tempered at a higher temp, if the edge flexes and returns to true, you know you have a good temper. Now the edge may not be hard enough to flex and return to true in its hardened state and may just fold due to the low carbon content, and if thats the case, you can temper the whole blade at a low temperature and call it good, or leave the edge at is maximum hardness, and temper just the spine with a torch (a small little propane torch will to the trick). Clean the blade off so you can see the heat oxidization colors occur, place the blade's edge in water to prevent it from heating, then heat the spine until you see the colors run. Continue heating until the colors move down towards the edge, but not to the edge. That will give you the best of both worlds, hardness and toughness. And is really the best choice for a spike knife.

Finally the last bit of advice I can give is to experiment with differenet methods and tempering temperatures until you find one that works best for that particular steel. This of course means destruction testing your blades, which you may not be willing to do at this stage, but its definately something that you should start doing if you plan to be making knives on a more serious level.

Hope that helps, feel free to ask for some clarification or expansion if needed and let us know how it turns out.

Graham Fredeen

[Farmer Phil]

Hey John,

I started out like your doing too, but after knocking up a couple of spike blades I went on to some better steel. I chose to do this for two reasons.

1. Better steel works differently, in that it's harder to move, easier to over heat, not so casually quenched in the slack tub, and it's heat treatable.
2. You can go through the whole knife making process: guards, handles, promels, etc.

I "progressed" from spikes to coil and leaf spring steel. Once again, a couple of blades out of that and I again reassessed my choice of steel and ended up getting some known steel, like 5160, 1084 & 52100. Also rounded up some handle material: stag, koa wood, brass, copper and stainless primarily.

Anyway, just some thoughts. Hope you post some pix! Oh ya, I'd just quench those spikes to get what ever hardening you can (not much really). No need to temper. It's just not gunna get that hard.

All the best, Phil

[sandpile]

FARMER PHIL is right. have fun with your spikes, then go to used or new spring steel(5160) making several blades and getting the feel of it(5160 is a great steel to practice with, it is real forgiving---52100 is a lot tougher to get right) and the advice here for your heat-treating. Everyone will be glad to assit.

On carbon steel--I hardly ever go over 350 to 400 degrees on the tempering.

Have fun and keep mashing.

chuck

[matt993fod]

WHOA!

How many heat treating steps have you been doing?!?!?

Really, 1040 is the simplest of steels. So little carbon that it really isnt that fussy. Simply normalize, heat to the point that the steel no longer exhibits magnetism, then quench in strong brine. You can get away with a brine quench on such a low carbon steel. Always test to make sure your hardening was successful. The file test is a good way to ROUGHLY make sure your blade is hardened.

Tempering to 545 degrees F is WAY too high for such a steel. It would never hold an edge! For a steel like 1040, you really only need to temper to a light yellow, simply as a light stress relieving process. Temper at 350-400 degrees F for about 30-45 minutes. An hour if you are particularly nervous about toughness.

Good luck!

[Ed Caffrey]

Jut not enough carbon there to create a usable blade. With a RR spike I suspect your closer to .030% carbon than .040%. To give an example, .040 is about the amount of carbon contained in a common wood screw, which can be easily twisted off/broken. Even with "Super Quench" you'll likely not get much more than an Rc hardness of 50, which will not hold an edge.
RR spikes are neat little things to practice on, and make interesting decorative things, but they do not make decent knife blades.

The basic steps to achieve a completed knife would be:

1. Hot Forge
2 Normalize/Thermal cycle
3. Anneal
4. Rough Grind
5. Harden
6. Temper
7. Finish/assemble

For anything below .050% carbon, I would recommend to only do a "stress relieving" heat/temper at 350F, anything higher than that and you will be softening the blade.

[steve sells]

Dont temper that high, Use 350 to 380F max

[m_brothers]

Okay, thanks steve, after this, I plan on moving onto leaf springs, then get taught, then start using real blade steel.

[Quenchcrack]

Point of reference: Normalizing will make the carbides smaller and distribute them more evenly. This will relieve stresses to a degree and make the hardness uniform when you quench it. Annealing makes the carbides bigger and the metal is softer than normalizing. The big carbides sequester carbon into areas and makes the hardening less uniform. As Ed said, forge, normalize to relieve stress, anneal to make it softer for grinding. Many smiths also normalize prior to hardening, too.

[Jmercier]

Normalizing after grinding and just prior to hardening is usually a good step. Normalizing is a stress reliever, and grinding steel actually does impart a good amount of stress.

a cycle of normalizing after grinding and before hardening can help to reduce failures during the quench (as can many other factors, but I'll avoid talking about pearlite, austenite, martensite, bainite, and the science of heat treating here)