Heat Treating Metal

[escher7]

I often see misinformation with regard to heat treating steel, whether for lock picks or other uses. I spent many years making custom knives, including fancy daggers and folding knives. I often travelled to knife shows, talked to the best custom makers and read every book on the subject.

Basic tool steel, such as O1 is treated for knives as follows:
- The object is heated in a forge, special oven or by a torch until it is cherry (bright) red.
- It is the quenched in oil to cool. (Hence the O1 designation.)
- At this point the steel is very hard and brittle.
- Because the tool will now be covered in black residue from the quenching it must be cleaned with abrasive paper for the next step.
- To temper the steel back down to a usable hardness, it is soaked (baked) in an oven (yes your mother's oven will work, as will a torch if you are careful) until the the oxide on the tool is the desired colour. For knives a straw colour is what you want. For picks, closer to the purple/blue colour which is spring steel.

Each steel has its own method of heat treating: O1 is oil quenched, W steels are water quenched, A1 is air quenched etc. The steel in hacksaw blades is an advanced form of metal often containing tungsten and other elements to toughen it. Other materials such as chromium are often added to prevent tarnishing (stainless steel). These steels cannot be heat treated by simple heating and quenching in oil. They require much more complicated methods. Therefore, when you are making picks from materials like hacksaw blades, old kitchen knives etc. it is crucial that you do not over-heat the metal or you will destroy the hardness, and will not be able to restore it easily.

I often see authors recommending that you heat any old steel and stick it in water to harden it with no regard to the type of steel or any indication as to how you must then temper the steel to a working hardness. (By the way, the word "temper" is often mis-used to mean the whole process of heat treating rather than the correct meaning of softening the metal after quenching it. When steel is quenched, it becomes as hard as a file and will actually shatter if you bang it on an anvil. Hence the need to temper it.)

Bottom line, unless you are working with a basic steel and you know what its proper treatment is, don't heat it red hot when grinding or you will likely ruin its properties. Dip it in a pan of water every so often to keep it cool and you will end up with a pick made of high grade steel that preserves its original working characteristic.

[Anavaree]

This is the quick reference I use when tempering my metals. I sometimes have access to a heat treating oven which is nice but otherwise a traditional oven will work but you have to watch the color change closely. once the heat starts to build up the heat increase and color change will happen crazy fast.

[LocksmithArmy]

most people will advise against this... but this is my method for not damaging the temper on metals I am grinding...

its quite simple really... when you take your base metal to the grinder... don't use gloves... or pliers or anything... hold that metal in your hands...

if the metal starts to burn your fingers, dunk it in the water... you will never come anywhere near "cherry red"
it hurts a bit, but after you make an entire pick (or 2 maybe) your fingers get used to the heat... and unless you are an idiot (or lacking nerve endings in your fingers) you wont ever do serious damage to yourself.

be careful not to slip into the grinding wheel... while you can touch it without damaging yourself you may slip in under the guard and get stuck, that could cause damage (i touch my wheel all the time without hurting but i would hate to get stuck under the guard and grind half my finger off in a couple seconds)

take it or leave it, thats a my way for not damaging the temper

[zeepia]

Thanks for the info provided so far in this thread, it will come handy in some projects!

Many might advice against this as well, I never use water to cool down what I grind. I use constant 8bar compressed air and keep the pick only with one hand. Metal doesn´t get too heated this way so I don´t use gloves either. Don´t try this unless you are sure you can do it right! Of course you could trim a compressed air pistol to a stand so that you don´t need hands to keep it at place. Also I don´t use grinding wheel but belt sander.

And if you use compressed air, make sure your surroundings are clean as you are providing a lot of oxygen contact with sparkles and make possible circumstances for fire!

[MBI]

I like using a wet grinder. The wheel turns at a lower RPM so it can take a little longer to shape things, but it gives me better control and never heats up.

[phrygianradar]

This is a great thread and I have been wondering how some of you guys make your picks. All the ones that I really liked (except one! fingers crossed) that I have made so far have broken , and I was wondering if I am getting the metal too hot or not hot enough or what. So far I have been doing the hold it in my hand and dunk it in water when it gets to hot to hold method. It could just be the crumby pieces of street bristle I am using.

[GWiens2001]

Have used a bench grinder with a cup of water for rapid rough shaping of picks. Every second or so, I dip the pick into the water. Never has a chance to get very hot, and the picks last. Used to get the metal hotter, and the pick would break under stress, but this does not seem to be a problem since I started using the water. Note, I never allow the metal to become hot enough to discolor.

Gordon

[femurat]

I use a wet grinder too

[mhole]

Don't use gloves when grinding picks - if your finger touches a grinder wheel it'll hurt some, and you might loose some skin, but you'll notice quickly, and pull away. If your glove touches a grinder wheel you can break a finger or get pulled into the wheel in a fraction of a second, and really injure yourself. Gloves are generally a bad idea when operating power tools which spin.