Tempering question, great HT explanation by STacy on Pg 2.

Atlas Knife Company

Atlas Knife Company

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Just got done heat treating an s30v Santoku. I can find soak times for 1650°, 1950°, and 450°, but no soak times for the cryo. It's currently in the oven backing at 450° for 2 hrs, then room temp then to cryo. How long should it stay in cryo?

If no answer, then I will do 5 minutes at cryo the first round and leave in the cryo until the dry ice is gone after the second batch.

Also, should I let it warm to room temp before putting in the oven for the second tempering, or just put it in cold?
 
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it is my understanding that the blade should go right to cyro after the plate quench and soak for hours . Most just leave them in over night .
 
Zaph, cryo should be done as a part of the quench. Doing it after a full temper will probably get you limited results. Remember that with cryo, you are trying to convert retained austenite that was left after the quench to martensite. A full tempering process will convert some RA, but the rest tends to stabilize. If you want to cryo, you should do so right after the quench or after a quick snap temper. As for time, I just leave it overnight.

--Nathan
 
Great, now I'm even more confused. I thought I had to go straight to the temper right after the quench? Leaving it in cryo overnight, I couldn't begin the temper until the next day.
 
i cannot remeber where i read up , But Cyro is 12- 24 hour .

at -180C and then - 300C

two step , while i had not try any of this . please verify the info by searching online cos i got it while reading up .

Good luck .

Not sure if it apply to the steel yo are using .
 
I missed the last line of Stacy's post. Thanks for all your help.

bladsmth said:
I found a large cooler at a yard sale for $1. The top hinges were broken, but the lid fit fine. I placed a section of Kaowool in it in a "U" position ( best way to describe it). I placed a metal pan (whole fish cooker from another yard sale) on the wool. Poured denatured alcohol ($10 for a gallon can from Home Depot) in the pan and add the dry ice chunks.
After giving the hardened blades a snap temper at 200F, I had chilled the blades in the freezer and kept them there until ready to place in the alcohol/dry ice mix. After placing the blades in the pan, I folded the wool over the pan and placed the cooler lid on with a brick on the top ( because my cooler wouldn't latch shut). Just leave it and go to bed. The next day all there is is a pan of alcohol with the blades in it. Pour the alcohol back into it's can and label it for "cryo". Give the blades a second temper and a third,because the snap temper really does not count.
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Gabaski said:
i cannot remeber where i read up , But Cyro is 12- 24 hour .

at -180C and then - 300C

two step , while i had not try any of this . please verify the info by searching online cos i got it while reading up .

Good luck .

Not sure if it apply to the steel yo are using .
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Those must be Farenheit temps since absolute zero is -273.15C.

Having noted that, we have used both dry ice and liquid nitrogen, with essentially similar results, and we have not used any two step cryo process. For time, while it appears results are all acheived after a few hours, we routinely leave them in overnight.

As for the OP remark about getting in to temper ASAP, I agree with that for Carbon steels - especially 1095 which is prone to breaking even when properly treated. No need to tempt the fracture demons more with a window of opportunity. ;)

For most of the air hardening steels, I don't think it's so important to get them straight into temper. I have heard from people that are reluctant to wait till the oven cools, but if we can leave them in cryo for hours or overnight, I'm pretty sure they won't see any more damage sitting on the bench overnight. If concerned, do a snap temper.

Rob!
 
OK, thanks Rob! BTW: Do you have anymore (1/16" or 3/32") x (2.5" or 3" s30v)? I want to make another one of these and liked buying steel from you last time. Also, I need something for a very slim prybar. I currently have one made of 6Al4V and use it to crack open laptop cases everyday. I was thinking of making something nicer. Keeping a sharp edge isn't necessary at all, but strength is a must. I'm thinking of a tool steel probably. Any chance you will be at Ashokan?


Last s30v I made and hardened, I had problems. It came out of the plate quench perfectly straight. But, I didn't temper it right away and it was warped by the next morning about 1/32". I just don't want the same thing to happen here because this is so thin at only 1/16". Dang, it's hard to flat grind that thin. This is going to be a wedding present and I don't really have time to make another one.
 
KnifeMaker.ca said:
Having noted that, we have used both dry ice and liquid nitrogen, with essentially similar results,
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May I ask what steels you are referring to here and how you determined that the results were similar? I am not calling your statement into question, just very interested in your results. I am roughing out a batch of A2 blades now and preparing to do my first run at cryo with dry ice. I am also planning a batch of cpm3v blades soon, and I am debating whether to send the latter out for HT to be sure the cryo is effective since LN does not seem to be in my immediate future. The price of the 3v is hard to justify unless you have confidence that the HT/cryo is geared to get the most out of it.
 
Time for more dry ice, and maybe a better cooler. A friend has a foam cooler that is 4" thick he got from a medical equipment supplier.
 
Justin King said:
May I ask what steels you are referring to here and how you determined that the results were similar?
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Sure Justin. The objective test is from the extra RHC points the rockwell tester shows, indicating (IMHO) more complete conversion and less RA. We also did some dye penetrant testing for cracks with the liquid nitrogen and found none. The subjective test is customer satisfaction.

We used dry ice and acetone, because it met the requirements of the data sheets without special equipment. The results we got were consistent with Crucible published tables. The problem was that the dry ice was all gone after 48 hours - so we bit the bullet for a dewar and started with liquid nitrogen. The hardness results are the same (as is the customer satisfaction) but the 20 litre dewar lasts 5 -6 weeks instead of 48 hours - so the liquid nitrogen is a no brainer for us.

Oh yes, you asked which steels. The answer is all air quench steels (yes 3V), 154cm, CPM154, S30V, RWL34, 440C, D2, CPM D2, ATS34, A2, Damasteel. I'm sure there are more, but those are what comes to mind. We never did RWL34 or Damasteel in dry ice.

We also do O1 in cryo, with either no difference or 1 RHC better - mainly because it meets the test of "do no harm". Carbon steels go straight to temper.

Rob!
 
The Number had alway been a little confusing for me Cos i so use to working in Degree C .

What ROb said might be correct as 300F.


like i said i cannot recall - but i think i saw something like -450F using Liquid Helium or something .

not sure if it possible in a un-control environment or if is even Safe .

but what i read is that Unless Deep CRYO treatment is Done . it would not show great improvement , and you are better off . Having a Good Oven and do a Good hardening and tempering process. cos if you DO it badly . what you get is just added Name that your Knife been Cryo treated but in fact the Steel does not improve Much . or rather a better control HT knife would be better .

All this is read up . so maybe you can go search it i found it online .

what i recell slightly is like 12 hour treatment and then 24 hour treatment both need to temper in heat before each process.

and the Deep cryo treatment DO improve the steel .
 
You're looking at far to complex treatments. Steels with lower than 1.00 % C see little benefit from cryo. For the reduction in retained austenite ,dry ice [at about -100 F] will help.Liquid nitrogen at -300 F will do more . You can go directly from quench to cryo .If you're nervous about cracking a "snap temper " at 300 F will a bit safer.
After cryo ALWAYS temper .After the cryo and temper little benefit is seen for further cryo for knife steels.
 
mete said:
After cryo ALWAYS temper .After the cryo and temper little benefit is seen for further cryo for knife steels.
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Mete: What do you mean here? My understanding was temper then cryo then temper then cryo then start hand sanding. Are you saying to cryo then temper, with temper being the last step instead of cryo?
 
Think of the Cryo as part of the quench process, just much lower in temperature. You should always temper after a cryo cycle .
 
Zaph, I think you had things a little mixed up. Heat to critical and hold the appropriate time, quench in the appropriate medium, cryo (if appropriate for the steel; snap temper before cryo if you like... I never have and have never had a blade crack *yet* ;) ), temper, and finish. No need for any more cryo.

--nathan
 
Understand the difference between "temper" and "snap temper" .Snap temper will make things a bit safer without stabilizing the RA. Temper at 350 F and above will stabilize most of the RA.
Cryo will transform RA to UNtempered martensite which must be tempered ! So the last operation is always temper.
 
OK, super confused now. You seem to all be saying to cryo between quench and tempering. Crucible's datasheet states to freeze between the two tempers. How badly did I screw it up by doing cryo between the tempers and not between the quench and temper? Should I finish the second temper or anneal and reharden?

Double temper at 400-750. Hold 2 hours minimum each time. A freezing treatment may be used between the first and second tempers. Freezing treatments help to maintain hardenability and must always be followed by at least one temper.
 
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