Heat damage grinding tools. Annealing Tempering Hardening

[pickmonger]

When grinding tools the heat generated can significantly change the properties of your metal stock.

To prevent this proper cooling is essential. Some dip the work in water, others have a spray of water or cutting oil and water.


Annealing - flexible

Tempering - springy

Hardening - brittle

Check out Heat Treatment of a Metal Bobby Pin to learn about the role of heat vs cooling on metal.

http://jchemed.chem.wisc.edu/JCESoft/CC ... /CD2R1.HTM

[Gordon Airporte]

That's a very nice, clear guide. It might be worth stickying, but we can't control whether the site stays up or moves or whatever.

[krept]

i just wanted to add that when annealing, the key is to cool the metal down as slowly as possible. Frequently, for 1/8"-1/4" thick barstock, the metal is heated to nonmagnetic and then buried in some insulating material. Vermiculite, available as a soil additive in the garden section of many stores, works fine. For barstock, it is generally left buried overnight and allowed to cool for at least 12 hours. Obviously for something that thick (a pin) it won't take that long... but it can't hurt.

For simple carbon steel, if you want to be more particular about the heat that your metal is, a magnet is used... when the steel reaches the point at which a magnet won't stick, this means that the residual carbon has properly dissolved in the iron matrix and that quenching, annealing, etc. can occur. If you just let it cool down to room temperature, it is called "normalizing" and is used for stress relief. Normalized steel comes halfway between annealed and tempered steel in terms of hardness and springiness.

Take note that the tempering stage is critical. If the steel is medium- to high-carbon, untempered, it is brittle and can easily crack.

A good, easy way to tell if you have hit the sweet spot in heat treating is if a) your steel is still relatively flexible and b) a file does not "bite" into the steel as much as it did before the heat treatment process.

That's a cool site... the photos definitely help. thanks.

Cheers

[krept]

Also wanted to add... when you are dealing with high carbon steels, quenching in cold water can easily cause the steel to fracture. Sometimes, microfractures will form and they will not be apparent until the steel is stressed. Additionally, tempering as soon as possible after the quench is recommended to help relieve the stress. (ask me how I know... I've broken some high carbon blades in this process... tens of hours of work down the drain).

If for some reason the water really screws up your steel, a lightweight motor oil or transmission fluid can be used. Ideally, you'll want to have it hot because if it is cold, there is a possiblity the glowing steel will cause an envelope of steam to surround the piece, so it won't cool as fast.... something about viscosity at higher temps works to cool the steel faster.

anyways... i'm done

[ericm115]

Resurrected.

So, I am trying to stiffen my thin wiperblade tensioners. They bend on me. I used a propane torch to get the tensioner cherry red before the bend and the quench in room-temp/coldish water. It's still too flexible.

I like a very stiff wrench. I tried today with a propane torch to get the wrench as hot and bright as it would go, and very quickly plunged it into icy water... no difference.. still bendable. Hrm. It should be brittle after that I thought.

So I used MAPP gas from work. It's much hotter. I used more ice. I got out a different wrench that I made the same way and got that sucker as hot as I could. I carried the torch and the wrench down as near the icy water as I could (there were two people working this experiment) before slamming it down into the icy water. I pulled it out and it bends like playdoh.

I even tried tempering... I very slowly heated another wrench so that as soon as it seemed like it wanted to glow, I moved the flame down to a different part of the wrench. I went up and down it till it had a nice "peacock blue" oxide layer on it (just like on that website linked to on this thread). I let it cool to room temperature in air. It took a while. It bent just like every other experiment I made.

What do I do?


em

[Shrub]

The problem is your trying to harden the wrong material,

You could try rubbing a bit of soap on the metal so its a thin cover and then heat it up until the soap turns brown, then quench,

If that works youve got something that is an alloy and not stainless,

If its stainless you will find a very thin section will always be floppy,

[CVScam]

I am sure there are people who can retemper wiper blade inserts but I am not one of them. I can heat them up for shaping and bending but I have had very little luck tempering them. I end up with picks that bend too easy or they are brittle or they seem fine untill I use them a few times then they break. I just leave them cold now and shape them very carefully not to get them hot. I have noticed some wiper blade inserts bend easier than others I guess it depends on what brand wiper it came from.

[bpc293]

water is not good for quenching when tempering because its flash point is 212 degrees most oil is around 450 - 550 so you should use a oil and pre heat the oil to about 150 degrees. you will get less vapor lock. when you plop your pick into cold water the water is boiling off the pick creating a vapor barrier. what krept told you was right on and always use the magnet trick because you will never now how hot it gets by eye. once it gets to hot and it grains its done.