Tempering.... and home made tools.

[MrB]

Yes, it is tempering. The previous posters and the link provided by D_Shane explain the process clearly. I remember learning about it in metalwork classes at school. Did you never hear anyone refer to knives as having "tempered steel blades"?

The goal of the heat treatment is to make your steel hard not soft, but tough not brittle. The initial quenching makes the steel very hard and very brittle. Tempering takes out some of the brittleness produced by quenching while still leaving the steel hard enough for its purpose. In the case of a lock pick, you want the metal hard enough not to bend too easily but tough enough not to snap in clumsy use.

[Jow]

is it better to air cool or quench during tempering? picks are so thin that i imagine heat transfere is very fast so does this make a difference as to wether you use air oil or water?

[MrB]

I doubt that it makes much difference. Home tempering like this is rather crude; it is not really a high precision process.

It would be best to experiment with some unmade blanks to learn what works best before trying it for real on any actual picks.

[MrB]

My memory is a bit sketchy but I seem to remember that when we learned about tempering we heated the piece on a hotplate rather than applying the flame directly. It was quite tricky to get the whole piece uniformly to the right straw colour without some parts going beyond straw to purple before other parts were even hot enough. It's a bit of a skill and you can count on ruining a few pieces before you get it right.

[Beginner]

is it better to air cool or quench during tempering? picks are so thin that i imagine heat transfere is very fast so does this make a difference as to wether you use air oil or water?

I think that it doesent make much difference. I allways let them air cool and they will cool down pretty fast. The process happens when you warm the metal up again, not in the cooling part. But if it cools too fast then it has that brittle quality again.

[Beginner]

My memory is a bit sketchy but I seem to remember that when we learned about tempering we heated the piece on a hotplate rather than applying the flame directly. It was quite tricky to get the whole piece uniformly to the right straw colour without some parts going beyond straw to purple before other parts were even hot enough. It's a bit of a skill and you can count on ruining a few pieces before you get it right.

Yes you can warm those up with oil, oven, hotplate, sand, lead path, salt etc.. but with home tempering we usually have only fire and oven(if hot enough). We used in school a welding torch, it is a bit tricky to try evenly warm the piece. But as said before it doesent have to be so precis with picks. If you just train enough you will learn to see when it has right temperatures. And ofcourse the metal has a big part about those temperatures.

[Beginner]

My memory is a bit sketchy but I seem to remember that when we learned about tempering we heated the piece on a hotplate rather than applying the flame directly. It was quite tricky to get the whole piece uniformly to the right straw colour without some parts going beyond straw to purple before other parts were even hot enough. It's a bit of a skill and you can count on ruining a few pieces before you get it right.

Yes you can warm those up with oil, oven, hotplate, sand, lead path, salt etc.. but with home tempering we usually have only fire and oven(if hot enough). We used in school a welding torch, it is a bit tricky to try evenly warm the piece. But as said before it doesent have to be so precis with picks. If you just train enough you will learn to see when it has right temperatures. And ofcourse the metal has a big part about deciding right temperatures.

[D_Shane]

Found a few things in the books that seem to fit rather well.

First, about as close to what we are useing here is spring steel rod that has been formed into a spring.

once the desired shape has been reached, it needs to be heated to a red color. Blue, purple ( higher heating) is used for materials that are not already spring steel. The entire piece should not be heated, only the thinned or manipulated area.... pick tips and tang. Both a torch and open fire were used. A torch is suggested if available for something the size of our picks. And not holding directly into the flame. The metal should not be instantly heated to red.

Quench in thin oil or trans fluid. Reheat to red, quench. repeat 3 - 4 times. Oven bake at broil setting / highest setting on a cookie sheet for 8- 10 minutes. Quench in room temp water.

Much of the book is for think steel, iron, tools and equipment used in farming., armor.. etc.

It doesn't just give a method for tempering to different points and different materials. Throughout each area as it explains it also tells why and what didn't work. As in oil cooled it slower, giving a softer usage, and the oven / final water quench puts a harder shell while leaving flex in the center. For thin sheets of metal is says thinner oil is better then motor oil. Hence, trans fluid.

[Beginner]

My street-bristtles aren't spring steel, it is normal carbonate steel.

[Romstar]

Does anybody search anymore?

I went through the whole hardening and tempering thing a while ago.

Go looking for the post.

Romstar

[Beginner]

I made some more test about bending these metals.

Here's the pic
http://tinypic.com/karzt

The one on the left is heated up and quickly cooled in water, I then locked it up with lockpliers and applyed about 5 kg force to the tip of the piece. It bent right in a 90 degree angle and is about to break.

One on the right is a piece that I didn't heat up. I again locked it and applied the same force to the tip of the metal. It bent right where the pliers were. It bent more, but it did come back up a little bit like spring steel.

Middle piece is again heated and cooled and then heated again like the one in my previous test. It did bend more but it also came back up like spring steel. You can see in that picture that it did bend in two places and this is because I wasn't able to heat the metal up evenly, so there are sections that are harder than other's

Hope that this will again help you to choose if you want to temper your pick's.

[quickpicks]

Would Motor oil work for quenching picks?

[Beginner]

Why would you like to use motor oil for such small piece of metals? water works fine.

[Romstar]

Why would you like to use motor oil for such small piece of metals? water works fine.

No, NO, NO

Water does NOT work just fine.

Go borrow a book from the library about this topic and you will find out EXACTLY why it isn't fine.

Just to give you a bit of a hint. Water vaporizes, and causes the metal to become brittle due to an issue known as "vapouring". When the hot metal touches the water, it turns it almost instantly to steam. The vapour barrier around the metal causes it to become brittle.

Oil can't be vapourized as easily, and thus the problem is minimized. Plain old fashioned LARD is a good substitute, as is light machine oil, 5w30 motor oil and even Cod liver oil.

This is a very prominent issue at these temperatures. It does not become a problem during grinding, as you haven't raised the temperature to the vapourization point.

For hardening, tempering, or any heat treating use oil or another liquid with a higher vapourization point.

[MrB]

Sorry Romstar, but I'm a little bit sceptical about "vapouring" leading to brittleness.

As I understand it the recommended quenching process for hardening depends on the exact grade of steel you have, and to some extent on the size of the item to be quenched. To do the job precisely, the rate of cooling and the final temperature are important and have to be just right.

Both water and oil can be correct for quenching and the choice of whichever one (or something else like air) depends on many things especially the recommendation for that grade of steel.

In general, a water bath cools things down faster than an oil bath. If small items are quenched in water the cooling may be too fast and lead to cracking, so then oil may be preferred.

When water vaporizes in contact with the hot metal, the steam formed is an insulator and slows the cooling (which would leave the metal too soft). To avoid this, pieces are usually stirred in the water to keep fresh water in contact with the metal. But the formation of steam and bubbles complicates matters and makes it harder to achieve even and properly regulated quenching. Water may also corrode the steel, especially if that grade is not designed for water quenching. Oil avoids these vaporization and corrosion problems and allows for better controlled quenching.

Now, the reality is that nobody really knows for sure the grade of steel in wiper blade inserts, or hacksaw blades, or street sweeper bristles. So everything really is a bit of guesswork and some experimentation is needed.

Oil might be better for the reasons noted, but room temperature or tepid water could be fine too. If you quench in water your steel will get corroded and scaled and you will have to clean and polish it afterwards. If you quench in oil your steel will get blackened. The mark of a true scientist is to experiment. Try it different ways and see how it turns out.

Finally, remember that red hot metal plunged into oil is a possible fire hazard. Be sure to have a LARGE bath of oil and be careful. Whether using oil or water, wear eye protection against spitting.