It's true, the terms and definitions tend to get out of control and I've seen this both in many texts and in technical conversations...
Here are some definitions taken from "The Heat Treater's Guide" which is the official publication of the ASM and AISI which gives detailed HT information for virtually every known common metal in production today:
Normalizing: "A homogenizing or grain refining treatment with the aim of full uniformity throughout the part". [Side note by me from further reading: In this condition, the metal will have no internal stresses. When starting with an unknown material, it should be normalized first. A piece that's been hardened before can be "reset" and rehardened after normalizing].
Annealing: "A generic term denoting a treatment consisting of heating to and holding at a suitable temperature, followed by cooling at a suitable rate; used primarily to soften metals and to produce desired changes in other properties or in microstructures".
Stress Relieving: "A process of heating uniformly to a particular temperature then cooling slowly. Often called stress annealing". [Side note from me from further reading: Heavy machining operations and/or welding can cause internal stress. When such operations are complete, stress relieving can be performed. Depending on the original hardness of the part, stress relieving can change the original hardness in which case, the part must be rehardened].
Tempering: "A process on a previously hardened or normalized steel primarily to increase ductility and toughness but also to increase grain size of the matrix". [Side note from me: Tempering is required after heat treating. In virtually all steels, the tempering must be done within 1 hour of heat treating and the part must not cool to below 150F between the heat treating and tempering steps. Many metals require two tempering steps where the second one should occur within 24 hours of the first. -BTW: I have experimented with and noted the differences when procedure is not followed].
I'd like to point out that the mediums used to cool, quench etc are entirely dependent on the material at hand. It's not always done in standing air... It should be done in accordance to what the material requires and it could range from air, to water, to hot oil to sand, ash or salt baths etc... Some materials (depending on size) require martempering and austempering which are two-stage quenching processes performed at different temperature ranges. It reduces the overall quenching shock on a part while still producing the desired hardness. In these cases, multiple mediums are frequently used.
Ray
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Marcel,
For practice, even less expensive metals are fine to work on. 1045 and 4140 come to mind. These are great steels to make things with. 4140 is basically a low-end tool steel. Also, you're going to need a hardness tester to know if you're doing things properly. Indeed, there a cost of entry to this game but, once you get past the hump, it's clear sailing.
ATF: The cheapest is the best. BTW: If you really want to work on tool steels, you really should use the proper oil quenchant -but in my case, I used ATF and it achieved the desired/predicted results.
Also, many (but not all) of the air and water tool steels have heat treating temperatures beyond the range of your oven. -Just giving you a head's up... Yes, those materials are easier to quench -at the cost of having higher HT temperatures -that's the trade off.
Ray
I missed this thread when it first appeared. Now that I have my heat treating ears up, I'm getting really fascinated and interested in producing some good hardened and tough parts. I love this hobby!
For a beginner like me, O1 seems to be the reccomended steel to practice on, Is there another common name for it? Where's the cheapest place to get 5 gals of tranny fluid? Does it matter what type it is? ie: dexron, type F etc?
Marcel
