How To Damasteel heat treat questions

K

knifeaficionado

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Jul 30, 2016
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Hello,

I got this heat treat recipe from Stacy(thanks!). I would like to ask what's the purpose of the cryo with liquid nitrogen and is there a way to harden damasteel with less steps that would produce decent hardness?

damasteel heat treatment:

Foil wrap blade with high temp foil

Stress relieve at 1200 F for 2 hr. Oven cool to 800 F ( turn off oven heat and let drop slowly in closed oven). Remove and air cool to ambient

Preheat oven to 1400 °F

Place blade in preheated oven and soak for 10 minutes to equalize

Ramp at 9999 to 1950°F

Austenitize at 1950 °F for 15 to 20 min

Plate quench

Snap temper at 325 °F for 1 hour

Cryo in LN for 12 hours

Temper at 500 °F for 2 hours

Second temper at 450 °F for 2 hours
 
Presumably the Mf or temperature where retained austenite is completely transformed to martensite is below what's achievable at -90 degrees (about the temps of dry ice and alcohol slurry). Others smarter than me should chime in, but depending on the steel and purpose of the knife, some retained austenite sometimes won't be detrimental though usually it's not desired.
 
I found this shorter recipe by Paul Bos:
Peter: The process I use is 1975 Deg. F. rapid air quench, Cryo @ -280 . Temper @ 425 Deg. F for 2 Hra @ temp. Repeat temper for 2 more hrs. R\C 60-61. Paul.

So would that be simply removing stress relieving, equalization and snap tempering?
any thoughts on how it could affect the outcome?
 
The cryo is the finish of the quench for high alloy stainless steels. Reaching at least -95°F is required. A dry ice bath would work if cryo isn't available. The steel needs to be cooled to -95°F to fully harden. The LN cryo step will add eta carbides and make the blade a bit harder and tougher.

The stress relief is optional. On long blades it may reduce any warping issues.

The snap temper can also be skipped. It removes some of the stress in the blade from the quench. This will prevent possible cracks in the cryo.

On a steel as expensive as Damasteel, I would do all the steps that will assure a great blade. Any customer or user will expect it to be at its max .... not merely "good enough".
 
Consider emailing Damasteel and see what they suggest for a process utilizing the tools that you have available.
 
Getting the steel down to - 100 F will get out most of the RA .Yes a bit of RA will provide some higher toughness . You could then skip the whole cryo steps . But as said someone wanting the best steel will probably want the best HT also. You could though reduce some of the times of the cryo but I wonder who has done detailed study of all the variables .
 
The average cost of electricity in the USA is $0.10 per KWH. That means a 3800 watt oven costs $0.38 an hour to run.

Now, that $0.38 /hr is at full blast. In normal HT use, it costs less per hour. At temper temps, it cost very little to run. The damasteel HT listed would probably cost $1.00-$2.00 in electricity. This is around 1% of the steel cost, 10% of the wood, and even less than the sandpaper cost on the knife.

Lets look at it from the other side. If you spend $2.00 on electricity per knife and do a HT on a knife M-F every week , you will spend about $45 a month for the extra electricity. Other HT costs, such as foil, dry-ice, or LN add a little more, but HT is still well below $5 a knife (less than $1 a knife if done in batches or ten).
You will also be making (and hopefully selling) about 22-23 knives a month. If you make only $50 a knife as profit, you are earning a steady $1000+ a month in profits. If they are damasteel knives, you probably are making $3-4K profit a month. Few of us sell a knife a day, but you can see that there is no loss in the small amount of electricity expense in doing a top notch HT.
 
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