is tempering and heat treat the same?

K

knifeaholic101

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Oct 17, 2005
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is being tempered the same as heat treated? does all steel need to be edge quenched and heat treated? does o1 tool steel need both edge quenced and heat treated? sorry about all the questions just trying to understand what needs what
 
Heat treating is just a general term for using heat to affect steel. You can heat treat to soften steel which is annealing. You can use it to harden it to a spring temper or to a glass like state for holding an edge. Tempering is heat treating to relieve stresses after hardening.

It all hinges on time and temperature of the steel. It is worthwhile to learn as much as you can about heat treating in order to make good quality knives that will stand up to what they may be used for.

Here is quick tutorial:

Heating to Critical Temp (CT) when the steel no longer is magnetic, and holding that temp for 12-24 hrs and slowly cooling will anneal it. If you bent it it would stay in the bent shape.

Heating to CT and air cooling will give it a spring or tool steel temper. If you bent it it would return back to shape, more or less.

Heating to CT and then rapidly cooling (quenching) will give it brittle glass like properties. The area quenched and the other area that is at tool steel temper will be a weak spot with streses. If you bent it it too much it would break.

Heating and holding at temps around 350-600 depending on the steel will relieve some of the stresses (tempering).

This is an over simplified synopsis of heat treating and the type of steel, size and many other factors will affect the outcome.

If a steel is labeled A-xxx it means it is an air hardening steel and does not need to be quenched.

If a steel is labeled W-xxx it means you can water quench to harden.

If a steel is labeled O-xxx it means it can be oil quenched.

Clear as mud?

I am sure other forumites will chime in with more info and maybe a bit more understandable.
 
It's great to ask questions...that is how you learn and there are a great bunch of folks to learn from here. The process if starting with annealed material is to get your blank close to net with all holes included, heat treat which has different techniques and temperatures for different steels. I will describe stainless or air hardening steel process since that is what I am more familiar with. ATS-34 for example, I wrap in foil then I heat treat it at 1950 F and rapid air quench, this will make the steel hard and somewhat brittle and can chip easily. This takes us to the tempering or drawing back of the steel which causes it to be less brittle, you loose a very little bit of hardness but it is needed to make the blade tough and stand up to use. I then double temper for example I will put the blades in at 850 F for 2 hours let cool to room temperature then go back in the oven at 850 F for another 2 hours. If I cryogenic treat the blades, I do it between heat treat and temper. This is a very simple explanation with out getting into martinizing, grain growth etc., I don't think you are ready for that yet. You have talked about 440C and 01 in your posts and they are 2 different animals, let us know what steel you have chosen and folks here can help. I heat treat stainless for other makers and if you need that service, let me know. Again heat treat, quench, temper is the order of things. Others can help on the edge treatment and clay for hamons etc. for the high carbon steels.
Hope this helps!
Jim
 
The answer is in your other post on the same question.

B Finnigan - mostly good info but a few corrections:
You don't want to hold the steel at critical for 12-24 hours in annealing.You want to bring it fully to critical temperature and allow it to cool to room temperature over a 12-24 hour period.This is to craete fine pearlite.
Bringing it to critical and allowing it to air cool is called "stress relieving".It is done prior to quench to remove stresses that may cause warping. (Spring temper is a higher temper than blade temper, and is done after quench.)
W series steels can be quenched in water,but in knife making it is better to use a fast oil.Water is still too violent a quench for the thin cross section of most knife blades.
Stacy
 
Generally you "harden" a blade by heating it up until a magnet will not stick to it (above 1,400 F) and then quenching it so that it cools quickly. If you were making a file you would be done. You get a very hard steel, but it will break if you drop it on the floor.

Tempering is to reheat the blade to somewhere around 1/3 that temperature for an hour or two and then allowing it to cool at a moderate rate. Tempering will make it less brittle.

The simplest "heat treat" would be a combination of hardening then tempering. You can add on more steps, but those are sort of a bare minimum (there are exceptions, but this is a simple core),

You can take a file and temper it if you want to make a knife. Simply stick the file in your kitchen oven at 375 degrees for an hour or so. Then you can grind it into a knife shape. (You want to use a good file like a Nicholson for this).

Edge quenching is a trick to make a blade's edge harder than the body. If you only stick the blade edge into your quenching liquid instead of the whole blade the edge will get hard while the remainder of the blade will be softer (it wasn't cooled fast enough to be fully hard). This method is seldom used in commercial knife making. Swamp Rat knives is one of the only manufacturers that does it. Custom makers do it. Generally you need to be working with a nonstainless and non-air hardening steel to do edge quenching. The result is a blade that is "differentially hardened". Different sections have different hardness.

O1 is no exception to the general hardening then tempering process. It is one of the steels that can be differentially hardened if you want to. It is not necessary to differentially harden it for most applications.
 
Tempering a file at 375 will still leave it very hard (too hard to file into a knife).If heated to non-magnetic and allowed to slowly cool in vermiculite,it will get soft.
 
When you temper you don't quench. It probably doesn't make a lot of difference, but you generally just let things air cool.
 
375 F has worked for me tempering files. I recently used it on a Nicholson which I believe is 1095 carbon steel alloy. If you do a quick quench on 1095 you need to temper it quickly or it may spontaneously crack. I think that Nicholson either did a slower quench or a low temperature temper to prevent this. Anyway I was able to temper at 375 degrees for 1 or 2 hours (I have forgotten). After that it cut with a file like it was around 58 RC.

So I think it is likely that you can temper files a bit quicker and at a bit lower temperature than if you fast quenched the blade yourself.
 
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