Steel versus....

T

TinyDee

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Dec 26, 2005
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I am about to begin plate quenching. Yeah, first time for me but what I have is 3/4 thick, 8 X 15 steel. Will that work okay? I can get aluminum but have found it difficult to find what I want. So, I am with this for now. Any help appreciated for sure.










x
 
Since air is the standard quenchant for stainless steels, steel plates will still be faster than air. The biggest reason aluminum is used is the speed it absorbs the heat and then recovers for another round. This is because it has a much higher coefficient of heat than steel does. Steel has a much higher coefficient than air, so it will do the job...just not as good as aluminum.
If all you have is steel - use it. Just leave the blades clamped in the plates until the plates are cool to the touch.

I read all the time of people putting the plates in the freezer. Sorry, but the difference between 0°F and 70°F is negligible to a 1900°F blade. I did the math fast in my head, and get something like a 3.5% difference in cooling rate. Since the plates have probably 100 times the thermal mass of the blade, this percentage will make no discernible difference in the time it takes to drop the blade to below 900°F. If you use a time of 30 seconds to make the drop ( it is probably closer to 10 seconds), the difference in time would be one second. Cold or not, the plates absorb the exact same amount of heat energy.
 
Putting plates in the freezer can cause condensate to form on the surface of the plate... Not usuly an issue, but water contacted by extreme heat in confined spaces can do some 'unique' things... No matter how small...

Plus, its like putting a knife in the freezer between tempering cycles and all the other discussion. IMHO, if temperatures normally seen in earth's atmosphere can significantly alter the metallurgy of a steel, I wouldn't want to use that steel for a knife blade anyway...
 
The thermal conductivity of aluminum is about three times greater than steel, but the specific heat (thermal mass) of steel is about three times greater than aluminum. So the aluminum conducts heat away faster, but it heat up faster too, so the actual difference in delta T (and therefor quench rates) is not as great as you might think. I expect the quality of the surface contact is more significant.

Steel quench plates are not very popular, but they are effective.
 
I have nothing to add, except to say that it's refreshing and fascinating to see discussion based on actual data, not just hearsay and old wive's tales. Thanks, gentlemen!
 
Another small thing to consider,make sure your steel plates are flat. Use a straight edge and check them. If they have a slight bow they will add that curve to your blades when you quench.

Stan
 
Would an aluminum plate with fins machined in the back side be more effective, or is it not worth the hassle to machine them in. I would think that the fins would create more surface area and allow quicker heat exchange. About how long does a blade need to be between the plates until it is cooled?
 
Don't bother yourself with fins. I've been plate quenching A2, D2, 154cm, and CPM steels with aluminum for 3 years now. The biggest reason for plates IMHO is so the blades don't warp or twist on you. Once they are black hot (around 900f) you can pull the top plate off. Though the martensite conversion is still happening, chances of the knife warping at that temp is about 0. Though, it doesn't hurt to keep them on until it's 125f and enough to handle and cut them out of your foil.
 
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