How To vacuum heat treating damasteel?

K

knifeaficionado

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Jul 30, 2016
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What would be the ideal heat treatment process for hardening damasteel to 60-62 HRC in vacuum oven?

Any direct experiences with this kind of oven and damasteel?

I would hope to get some improvement to our "recipe" since last vacuum hardening process got us only 57 HRC.
 
Is it OK to do the cryo a few days after austenizing or does it have to be done right away?

Any real benefit from the oil quench instead of air cooling?
 
Cryo needs to be done right away, continuous cool down. Austenite can stabilize if given time.

Oil or plate quench would be good.

Hoss
 
When I do it myself, I austenitize at 1950F in a sealed packet in the regular HT oven. Plate quench, cool to room temp, directly into dry ice bath ( -100F) then temper twice at 400F. I get Rc 60-61.
 
I plate quench the damasteel I’ve worked with. If You haven’t already done one ht yet, You may want to test with rwl-34 as the damasteel is pricey IMO
 
Thanks,

what is the difference of tempering once or twice and is the foil necessary if using vacuum oven?

Stacey, I have this heat treatment written down based on your earlier instructions, should this achieve 60-64HRC with 1.7mm thick blade and would austenizing time longer be better? These temps are from damasteel data sheet for 63 HRC blade


1.Foil wrap blade with high temp foil
2.Stress relieve at 650 Celsius for 2 hr. Oven cool to 425 C Remove and air cool to ambient.
3.Preheat oven to 760 C
4.Place blade in preheated oven and soak for 10 minutes to equalize
5.Ramp at 9999 to 1080 C
6.Once the oven has reached 1080 celsius, austenize for 5 minutes
7. Remove the blades from the oven and plate quench
8. Cold treatment with cryo(liquid nitrogen) or dry ice method for 1.5 hours.
9. let warm to room temperature in air
10. temper at 175 Celsius for 2 hours
 
I would soak at 1080C for 15 to 20 minutes.
Two tempers are pretty much a requirement. Especially when dealing with RA.
 
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I don’t have a vacuum oven, I just put argon gas into the foil pouch to achieve an inert atmosphere. I used the same recipe you listed above from the damasteel website, except I left the blades in the liquid nitrogen overnight, and achieved exactly 63RC. I wouldn’t try to save money on the power bill, by skipping the second temper. Here is my video if you don’t care to spare nine minutes to watch it.

 
I don’t have a vacuum oven!
I use the same procedure as Stacy and the results are the same. I use this procedure for RWL34
 
RA is Retained Austenite.
When you HT steel, it becomes austenite above 1400F ( roughly).
When you quench steel, it drops below 1000F fast enough to stay austenite … called super-cooled austenite.
As it reaches around 400F (the Ms point) it starts to convert to Martensite … which is what you want for a knife blade.
If the steel is simple, the conversion to martensite is finished by the time it cools to room temp (the Mf point). If there is a lot of alloying, the conversion may not end until -100F. If you quit at room temp, the amount of austenite remaining unconverted is called % Retained Austenite. Tempering removes some of this, and that is part of why you need two tempers. Cooling to -100F with dry ice, or -300F in cryo will convert most of the RA to martensite. It should be done immediately after cooling to room temp as part of the continuous cooling from 400F.
All steel with high alloy will have a small percentage RA even after cryo. This isn't a problem, as a small amount of RA actually makes the blade tougher.

Upper range tempering (900-1000F) of knife blades isn't normally done. It is occasionally used when cryo isn't available, but I generally recommend using the 400-500F range. In industry, where toughness is more important, high alloy steels are normally tempered in the upper range.
 
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Stacy thanks for the useful info. In case I won't be able to use sub-zero temperatures, other than the freezer, what changes to the temperatures in the above HT process should I do, only change tempering temperature to 950 fahrenheit?
 
As I said, I would not use the upper range on knves unless there is a special reason.

If you do HT with nothing more than an stay in the freezer, drop the temper to 375F and you will be fine.

A gallon of denatured alcohol from Home Depot costs about $15. You can use it over and over again for sub-zero cooling. It is also the proper solvent for cleaning up epoxy before it sets.
Do sub-zero treatment as soon as possible after the blade cools to room temp from then quench.
You put the alcohol in a metal pan that will hold your knife and have room for the dry ice. Set the knife blade in the pan half full of alcohol. Break up 2 or three pounds of dry ice (you can get it at many grocery stores) and put the dust and chunks in the pan of alcohol. It will boil and smoke ... that is normal. Let the blade sit in the pan until it stops bubbling in an hour or so. Take it out (it will be very cold) and let return to room temperature. Temper immediately at 375F for two hours twice.
 
knifeaficionado said:
Stacy thanks for the useful info. In case I won't be able to use sub-zero temperatures, other than the freezer, what changes to the temperatures in the above HT process should I do, only change tempering temperature to 950 fahrenheit?
Click to expand...
I recently used higher tempering temps of 1050 F to bring a Damasteel slipjoint spring down to 50 RC
I don't think you want that higher tempering temp.

page 3 here has a tempering diagram of RWL-34 - http://michaelwest.dk/knive/rwl34-datasheet.pdf
 
That is interesting info. I haven't seen that sheet before. I wonder about the "High temperature tempering for Maximum Edge Sharpness" statement?

Larrin - you got any info or comments on this?
 
Stacy E. Apelt - Bladesmith said:
That is interesting info. I haven't seen that sheet before. I wonder about the "High temperature tempering for Maximum Edge Sharpness" statement?

Larrin - you got any info or comments on this?
Click to expand...

The only thing I can think of is the correlation between higher hardness and better support for fine edges. Our testing is showing better toughness at equivalent hardness with low temper protocol in every steel tested except M2 so far.
 
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