DIY Tempered Carbon Steel Picks (great for any hand tool)

[unjust]

i'm not even going to begin to go into all of the confusion and misinformation as to metal treatments in this thread.

very simply put:
we need relatively little strength in out tools and a bit of springyness. brittle hard steel is our enemy.

for 90% of us making our own picks, hacksaw blades or plumbing snake retreated to allow for overheating from grinding is fine.

the only practical reason i can think of to put heated oil on a pick is to use a hardening oil to apply a protective surface finish.

[hiaxis]

There is no way that you are going to incorporate carbon into the crystalline structure of the iron by letting oil burn on the surface of the metal. If the steel was hot enough, you might...might convince me that you could get some carbon into the surface a few molecules deep but never deep enough to alter the properties of the steel. And since the combustion would be so dirty, you'd probably just incorporate impurities. No biggie though, that few molecules would rub off just sliding the picks in and out of their case.

However, oil quenching is often used to harden steel. It's the rapid cooling, not the carbon in the oil that makes the steel harder. Different steels behave differently but typically, the faster steel cools, the smaller the crystalline structures in the steel are. The smaller these crystals, the harder (more brittle) the steel will be. To get the "right" hardness, you need to know which steel, quench at the "right" temperature, and quench in the "right" liquid.

Google "tempering steel" and I'm sure you'll find charts that let you use the color of the steel to determine when it's the "right" temperature for your application.

Most oil tempering is done around 450 to 600 degrees. If you're catching the oil on fire, you're above the ignition point of motor oil which I'm sure is too hot to temper correctly.

By the way, slowly cooling steel to soften it is called Annealing, tempering is cooling quickly to harden steel.

maintenanceguy is pretty close. To harden, there has to be enough carbon already in the structure to harden a steel all the way through. Some info on what carbon actually does to the metal's structure is in a previous post I made here: viewtopic.php?t=20107&start=15 However, you can case harden (surface harden) a low carbon steel by heating it to the transition temp while its surrounded by something high in carbon, such as charcoal. The carbon WILL enter the structure of the material and assuming a proper quench, the surface hardness will increase.

It was mentioned in a previous post that quenching in oil vs. water makes no difference. This is incorrect. What you quench in will affect the hardness of the material because every fluid used in quenching transfers heat out of the steel at a different rate. Heating a medium carbon steel up to its transition temperature (around 1600 deg F) changes its metallic structure, allowing more carbon to become trapped in solution. As the steel is quenched, the carbon is locked into the now altered structure. The relatively large carbon atoms now trapped in the modified structure prevent what's known as "dislocation" in the metal's structure. This resistance to movement on the atomic scale is what affects a material's hardness, toughness, ultimate stress, yield stress, impact resistance, etc.

Quenching "freezes" the structure and prevents it from returning to its previous state. The faster you cool the steel, the harder it will be (in most cases). Salt water generally has the highest heat tansfer coefficient compared to the others I list, followed by fresh water, oils, air, and in some cases sand. Quenching with salt water will result in the highest hardness possible, and the resulting hardness goes down as you go through the list. The slower the material cools, the more the structure will return to its previous state, thus changing the resulting hardness.

Also, tempering isn't the hardening process itself. Tempering is the process that follows hardening to make the material tougher instead of brittle. The temps quoted above are correct. In the case of picks, tough is what we want, not hard!

Hope that helps clear some things up.
Brian

[copeman]

as far as used motor oil goes alot of garage knifemakers use it for hardening. alot of good info can be found on bladeforums.com if its against the rules to have that website in my post im sorry.

[phantomhck]

not sure if this has been said before, or how well in this post, but if you're already working with a high-carbon tool steel, you probably don't want to add more carbon as that would just make it more brittle, but still stronger. The power of the tool steel is that it won't bend (at least not permanently).
if anything, I might heat treat my tools when I make them, but that all depends on the steel.
I might op for a stainless steel that can be heat and carbon treated (SS440) or a variation of that classified as tool steel. Depending on the thickness of the tool (height vs. length) you might want to only carbonize the edge of the tool so that's strong but the outer side still has the flexible properties so it won't break.
You should be able to feel your pick bend and that's obvious that it's way too much force.
also, simply for tempering the steel, you might want to just use water instead of oil, so that you don't put way too much unwanted carbon in the steel making it weak.

There's probably some info I forgot to add, but let me know if anyone wants to know more.

[ForFun]

when tempering the best liquid to use, if your makeing your picks out of some kind of steel , when you heat them up to what ever temp quinch them in used motor oil, the oil will ignite so be careful but all of the excess carbon in the oil is absorbed into the metal resulting in a DIY tempered carbon steel pick.

I use to buy something called Quinch Oil. I don't know what the number or specifications were but all I needed to do to get some was call up and order a 5 gallon can of "Quinch Oil". It never caught on fire!
I had some customers who wanted the teeth on their sprockets case hardened. I used a Rosebud tip on a torch to take the teeth to cherry red and then drop the sprocket of into a half filled bucket of the quinch oil. It worked great but I only did this on a brand called Martin as that brand was known to have the right amount of carbon. You could really tell if you had done it right by just putting a file to a tooth. I think "Quinch Oil' is the way to go if for no other reason then safety.

[Shrub]

not sure if this has been said before, or how well in this post,

I will give you a bit of advice here and now that is gogin to save you some flaming and abuse in the future if you wish to stick around,

Do not post on a thread if you cant be arsed reading it first

[quicksilver]

I am not debating the fact that metals can be hardened by heating and quenching. This is due to deliberate alteration of the crystal structure of the metal, but this idea of carborizing the outer layer of metal by quenching in dirty oil seems questionable to me. Especially if the same metal is then washed(etched) in dilute sulfuric acid - removing any thin coating that may exist.

Actually the processes being described are more accurately stated to be annealing. Having generally made most of my picks I can only add what is both my opinion and experience. There is SOME need for spring in the overall metallurgical make-up of a lock pick (for ME). Spring is indeed altered or imparted by levels of carbon in the steel. however it is also reflected to a greater extent in the crystal structure of the steel. That crystal structure is altered by impact (hammering) after finding the level of carbon existent the steel. This process is also sheared by non-ferris metals (crystal structure; hardening via hammering, etc). Spring is quite useful (IMO) due to the flex which can keep straight during picking.

I have even made a bronze pick (not brass) as a test. And it was quite "springy" & due to the strength: successful. However it will still score a lock of brass on a near microscopic level with a gentle hand.

It is not so much the carbon but the COMBINATION of the C & the crystal structure which determines "strength" (which is too generalist for most people). I have often started with "SCROLL SAW" blades for my picks as they have a wonderful size, shape, and "spring" that if LEFT ALONE with a cool stone wheel or file will yield a very fine pick of great flex and thin size. In fact, scroll saw and cooping saw blades can be found at .025-.020 to duplicate most all commercial picks.

[hiaxis]

Good post shrub. Having done a lot of metal work, hardening with various methods, etc., I agree we want "springiness" in picks but don't agree that the processes previously described (unless I'm missing something) are annealing.

The process known as annealing is used to soften a material, not harden it by quenching, carburizing(surface hardening), work hardening(as you describe as hammering or peening), etc. When annealing, you bring it up to trans. temp. for the material in question, hold it there for a long period of time, then cool it down VERY slowly to ensure the material is as soft as possible by removing the carbon from the crystal structure and allowing it to return back to a body centered cubic (a crystal structure in steels).

The BCC structure is better known as ferrite, as opposed to martensite (the structure that results from hardening). The BCC crystal structure will not hold very much carbon, so the material is soft. The carbon is still in the steel, it's just not an integral part of the crystal structure. However, the martensite structure can and will hold enough carbon to significantly alter the crystal structure on a microscopic level, increasing the hardness. Rapidly cooling, aka quenching simply ensures the structure is "frozen" where we want it.....as a body centered tetragonal.

I think what we're really after with picks is what's known as toughness. What is toughness? That's a question that most will answer by saying "I don't know, but I'll know when I see it." Toughness is hard to quantify but in short, it's a measure of how much energy the steel can absorb. A steel can be extremely hard but not be tough. We need to find a balance between hardness and flexibility to get the toughness we're after.

How do we do that with our picks? Start out with a medium carbon steel. Shape it, file it, and work it until you get it exactly where you want it. Then, through harden it by heating it above the transition temp for your material and quench it in water. Your pick will now be pretty darn hard, but brittle. To get the toughness we're after, we now need to temper the pick.

To temper, we normally heat the material to between 700 and 1100 deg F and hold it there until some of carbon in the martensite moves through the material on an atomic level to form pearlite. The now altered material is still hard, but it's now also tough. It can flex, spring, and be beat on without fear of cracking (to a point).

I'm fortunate to have access to a heat treat oven but how do we do this at home? A decent job can be done with an acetylene torch, a temp. gun, and patience. Controlling a material's hardness, toughness, and other properties is a very scientific process but it can be done with simple tools and some knowledge. Blacksmiths have done it by eye for hundreds of years.....

One last point on Shrub's last paragraph, you're right about the crystal structure controlling the hardness and toughness (by preventing dislocation) but it's the carbon itself that alters the structure when through hardening. If there's very little carbon in the steel, heating and quenching the steel simply won't increase the hardness. As you mention, peening will increase the surface hardness by mechanically altering the structure while leaving the material below unaltered, providing a nice blend of hardness and flexibility.

I apologize if this is too long winded but to understand how to get the mechanical properties we want, I personally think it's important to understand how and why it works. If we don't understand it, how can we control it?

[hiaxis]

woops, my apologies. I guess I was addressing quicksilver, not shrub. Sorry!

[phantomhck]

not sure if this has been said before, or how well in this post,

I will give you a bit of advice here and now that is gogin to save you some flaming and abuse in the future if you wish to stick around,

Do not post on a thread if you cant be arsed reading it first

I didn't mean that I didn't read it, but that I don't know if everyone understands metallurgy things so I would explain it differently.
Thanks for the tip though.
But anyways, I would just get a sheet of spring steel (as that's what's most commonly used in picks) and trace and cut out the picks. I wouldn't bother too much with heat or carbon treating then because there's a great chance you'll mess something up. Plus, tool steel is specifically made just for that kind of purpose that you're using it for so it's better not to alter it.

[metalking00]

I feel the need to add some bit of my own here, since I am a blacksmith and bladesmith.

If you havent spent a long time making knives (or springs), then its very likely that you dont fully understand how to heat treat a given metal to a given consistency. Its not enough to heat it to an unknown temperature and quench it in a liquid of also unknown temperature. While it is my practice to quench blades in an oil-wax mix (the wax makes it spillproof when not in use), it is not to add carbon to the metal. It simply doesnt work that way. You start with a high carbon steel, end with high carbon steel. quenching in oil wont improve your metal at all.

Picks are too thin to put into the oil from heat treating heat (Heat until it is nonmagnetic). To fix this, you might try the technique that japanese bladesmiths use to temper their works. Encase the metal in a thin layer of clay (there is a special clay that doesnt crack off from the thermal shock), and then quench. The clay creates a barrier between the quenchant and the metal, slowing the cooling to prevent the metal from becoming brittle, while not slowing it enough to cause the metal to become soft. The end result is a nice springy pick.

More work than it needs to be... get some spring steel as said before and shape using frequent quenching.


In response to maintenanceguy, while that is the tempering temperature for many metals, what is outlined seems to be more of a heat-treating. Heat treating gives a metal a certain property (springiness, brittle, etc.) while tempering relieves stress risers within the metal allowing it to "relax" without losing its heat treated properties.

Heat treating is cooling quickly (within specs for a given desired property) while tempering is heating to relieve internal stresses that may cause the metal to crack or fracture during use. Can't have one without the other, but they are quite different.

[Matt-the-rat]

Used motor oil is appraently very good for doing this. like rai said, I think it leaves a colour in the surface of the metal, please correct me if i am wrong.

[metalking00]

Used motor oil is good, but its the least important factor in the process

[XOR]

Seen some good and not so good posts here. I make knives as a hobby so let me say a few things.

1) Not all steel can be hardened. Only high carbon steel can be hardened. If you want to see if the steel you're using is high carbon or not a simple test is to touch it to a bench grinder. If it throws off a large shower of short sparks it is probably high enough carbon to harden.

2) Hardening involves heating the steel up to the Curie point or "in solution". This is usually done with a forge or good oxy/acetylene torch setup. This usually means having the metal red/red-orange all the way through. You can tell when you reach this point when a magnet no longer sticks to the heated object. Many blade smiths keep a magnet stuck right near their forge to test for this. When metal is heated to a point where it can be hardened it becomes non-magnetic.

3) Once you reach the Curie point you must immediately take the metal and quench it. Oil is best for this (I use veterinary grade mineral oil - available at any farm store). Oil flare ups can happen (not usually with mineral oil though) so be prepared to have something to extinguish/cover your quench tank. Water can frequently cool too quickly and cause cracks depending on what grade steel you're using so I think you should avoid it.

4) Lock picks are going to be probably too thin to harden properly. They'll probably warp when you quench them. If you want to try it anyway be sure you dip the pick in the oil but DON'T stir it around. Hold it absolutely still so the oil quench cools as evenly as possible.

5) Once the pick is hardened you should temper it. Tempering draws out the hardness and puts spring back into the metal. The tempering times and temperatures vary on the steel. I have a used toaster oven for this and I'll temper 1084 (or higher) steel by heating it to 375 degrees for one hour, then allow it to cool to room temperature and then heat it again at 375 for one hour and cool for two more times (three times total). You can use your kitchen oven to do this too but it may smell some if you still have oil on the metal. Before you temper the steel you should clean it off to the shiny metal with a wire brush, sand paper, wire wheel, etc. If you use power tools do NOT allow them to heat the metal up. Go slowly and dip the tool in water to keep it cool. If you heat it up with a power tool you'll ruin the heat treat and will have to do it over.

6) A properly hardened/tempered piece of steel should have a straw color when you take it out of the oven.

7) You can now clean up the tool but again DON'T heat it up by using power tools/grinders. Keep it cool with water and go slow. If you go up to the grinder and start getting it hot you'll wreck the temper and will again have to start over.

8 ) If you do mess up the temper by getting it hot again you'll probably wreck the tool in the process of trying to redo it so it's best to be careful.

The most important things to remember are:

A) If it's not high carbon steel it won't harden.
B) You need to get it hot enough to be non-magnetic before you quench.
C) You need to temper it to give it springy-ness and keep it from cracking.
D) DON'T heat up the tool with power tools or you'll wreck the temper.

Best Option of All:

E) Avoid all of this mess and just get pre-hardened/tempered spring steel pieces and work on them slowly and again NOT heating them up with power tools.

Hope that helps.

[XOR]

Yikes. I'm coming off as a complete newbie to forums posting when I'm really not. I have no idea why this site is double posting. Sorry again!