tempering vs heat treating

[Hoodoo]

Can someone please tell me the difference between tempering and heat treating? I was reading an article by Wayne Goddard the other day and he said you can temper a knife in a toaster oven. But heat treating, as I understand it, requires much higher temperatures. What's the difference and when do you need to do either?

I am currently making a knife out of a lawn edger blade. It's my first knife and it's pretty crude but what the hey. I'm wondering if I need to pop it in the toaster oven, maybe put some jam or butter on it... whatever. I dunno. If I toast it in my oven, how long should I leave it in. I'm assuming it's some kind of high carbon steel that has already been hardened.

Thanks,


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Hoodoo

The low, hoarse purr of the whirling stone—the light-press’d blade,
Diffusing, dropping, sideways-darting, in tiny showers of gold,
Sparkles from the wheel.

Walt Whitman

 

[Jerry Hossom]

HooDoo, the meanings have wandered around over the years. Tempering is generally considered to be that part of heat treating, where after the steel is hardened at around 1500-2100 degrees and quenched back to near room temperature or even cryogenically, it's final hardness is achieved by soaking it at temperatures in the 300-1000 degree range. As quenched, the steel is too hard and brittle to be useful. Tempering lowers that hardness and refines the grain structure to make the steel more uniform and less brittle.

Some use the terms interchangeably, but more accurately heat treating is the whole process. Tempering is just the final part.

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Jerry Hossom
www.hossom.com

 

[Ed Caffrey]

Hoodoo,

Generally, "heat treating" is a term used to label the overall process of normailizing, annealing, hardening, and tempering, (and sometimes sub-zero treating)
Heres the low-down on each of the above from the prospective of forging...........
Normailizing: When steel is forged or ground, internal stress is built up within the steel's matrix. Normailizing is accomplished by heating the steel to just below critical temp and allowing it to cool to room temp, in still air. This relaxes the stresses. Sort of like you or I streching after a long car ride.
Annealing: Simply stated, this operation, when done properly, places the steel in it's softest state, with a very fine grain structure. This is accomplished by heating the steel to critical temp, and cooling very slowly, by placing it in some type of insulating enviroment (I use vermiculite)
Hardening: Taking steel to it's hardest possible state. Achieved by heating to critical temp, and quenching in a rapid cooling media. (at this point the steel is very hard, but also brittle, this is the reason for tempering)
Tempering: This is a controled softening which brings the steel's hardness to a workable level. This step is accomplished by "baking" the steel (what temp depends on steel type and composition) for a given time to achieve a mixture of hardness and durability for the chosen task(s) of the steel. There are other steps, and combinations of steps that can be used, but that is basically what folks refer to when they use the term "heat treatment". Take Care!

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Ed Caffrey
"The Montana Bladesmith"
www.caffreyknives.com

 

[Hoodoo]

Wow! That was undoubtedly the quickest couple of replies I've ever received in BF. You guy's are the best and so is BF. I know I wouldn't be having fun making knives right now if it wasn't for BF. What a resource!

Thanks again, guys! I appreciate you taking the time to give me such detailed information.



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Hoodoo

The low, hoarse purr of the whirling stone—the light-press’d blade,
Diffusing, dropping, sideways-darting, in tiny showers of gold,
Sparkles from the wheel.

Walt Whitman