quenchig O1 steel

AJH_Knives

Well-Known Member
Hey guys, sitting here at work thinking about what the metallurgist at Starrett steel told me about heat treating their O1. He said after HT and oil quench, when the knife is at room temp to toss them in the deep freeze or dry ice if I wanted too. ( I am paraphrasing here) My question is after the initial quench, the steel is still too hot to touch. what would happen if you dunked that in water, say like cold tap water? would that cause any problems?
 
You will produce stress in the steel as the thinner parts cool off faster and contract more than the thicker parts will. Whether or not this will crack the blade will depend on the temperature of the blade and the water and the geometry of the blade. If O1 can benefit from cryotreatment I doubt that the kitchen freezer will get get the job done. A bath of dry ice and alcohol or acetone might be beneficial but I don't think that O1 is complex enough of an alloy. Do it if you want. It won't do any harm. Just play it safe and alloy the steel to get to ambient temperature before plunging it into a cold bath. It doesn't take all that long. If you don't have the time to wait for it to cool where are you going to find the time to make a new blade? You wouldn't believe how many times I heard a patient start to explain how an accident happened and his/her first words were "I was in a hurry".

Doug
 
If you don't have the time to wait for it to cool where are you going to find the time to make a new blade? You wouldn't believe how many times I heard a patient start to explain how an accident happened and his/her first words were "I was in a hurry".

Doug
I hear you, they will cool fast, because I'll be out in the back yard heat treating them!!!
 
Aaron,
Below was copied from Uddeholm O1 data sheet. You can cold treat, (not cryo treat as with LN2) with dry ice at -110F in an insulated container and gain some reasonable increase in wear resistance. I have seen articles on using an acetone bath but could just put block of dry ice on top of blades in a cooler for 3-4 hours then do your temper. Also attached a link to a PDF on cold and cryo treating- look at second page where talks about Cold Treating.

Sub-zero treatment
Immediately after quenching the piece should be
sub-zero treated to between –95 to –110°F (–70
and –80°C), soaking time 3–4 hours, followed by
tempering or aging. Sub-zero treatment will give a
hardness increase of 1–3 HRC. Avoid intricate
shapes as there will be risk of cracking.
http://www.energy.ca.gov/process/pubs/cryog_processing_tc113571.pdf
 
One caution about these data sheets, they generally refer to pieces of steel thicker than knife blades. Also knife blades qualify as irregular and probably the intricate shapes referred to above. Also be aware that the best Rockwell hardness testers only have a precision of ± 2 HRc so any improvement in hardness is marginal. I would still advise that the blade be allowed to cool to ambient temperature before being subjected to cryotreatment to prevent cracking due to it's irregular shape. The dry ice in alcohol or acetone will transfer heat much better than sandwiching the blade between blocks of dry ice.

Doug
 
One caution about these data sheets, they generally refer to pieces of steel thicker than knife blades. Also knife blades qualify as irregular and probably the intricate shapes referred to above. Also be aware that the best Rockwell hardness testers only have a precision of ± 2 HRc so any improvement in hardness is marginal...

NIST type specs list a +/- of 1 point variance in Rockwell calibrations, however the test blocks often will have a 2 point swing. I have found this to be a general average since one can be very fastidious on the upkeep and calibration of a good tester with top of the line test blocks (just one will probably not get you tighter than 2, but triangulating off several will) and get some pretty precise and consistent readings, but you have to be fairly OCD for it. I proabaly have close to half a dozen test blocks and never take less than 5 readings if it really counts, but then there is that OCD thing again:3:

I was thinking pretty much the same thing on the shapes considered in other industries Doug. I am not usually of the line of thinking that knife shapes negate industrial steel specs, but in matters of heating and cooling rates it cannot be ignored entirely. Freezing the blades probably can’t hurt, but I have never found it necessary with O-1. Barring over-soaking or over-heating there should be no problem achieving 65-66 HRC with knife shaped cross sections. Industry will have much differently shaped parts and thickness, and cooling rates will be, well, industrial. With perhaps in the range of 6-8% retained austenite, you are really pushing the point of diminishing returns. If one has the room for 2 or more points gain in HRC, I would adjust the soak temp and time for the quickest fix, as it strongly suggests greater than usual retained austenite in O-1. And if one does get such a gain from cold treatments it confirms the conversion of a problematic amount of retained austenite that would lead me to review my soak times and temps for a simple little knife blade.

Ausbrooks, I very much like that PDF you linked to, I saved it away in my library for future use. It takes a very refreshing objective approach to the subject and sticks with verifiable facts as much as possible, while pointing out the large amounts of unsubstantiated claims regarding cryo. Very fair and concise, a rare gem in the literature on the topic.
 
Kevin, thanks for the update on the Rockwell precision. I'm from a technical background and the rule is that if you can't prove it, it doesn't exist. So if you calibration block is only good for ±2 HRc....Moral of the story, get good calibration blocks. BTW, OCD rocks.:s11798:

Doug
 
...So if your calibration block is only good for ±2 HRc....Moral of the story, get good calibration blocks...

Absolutely, since your tester is only as good as those blocks it is one area where you just cannot skimp. For accuracy, a $5,000 dollar Wilson machine with cheap blocks isn't worth half what a $900 Chinese machine with good blocks is worth. Also I have had clients who had me do some work for them laugh at the 10 or 12 Rockwell dimples on the piece I tested for them. They say the laughter is because I am the only one they would expect to see that many tests from, which is disturbing to me since what you rightly point out makes averaging necessary for truly accurate readings and if most folks are only taking one reading it makes me wonder how many people have reliable numbers at all. My numbers are also rarely even whole numbers either since precise averaging often gives me something like 62.73, now of course my tester dial doesn't have that many increments but the spread sheet I enter my numbers into does. And if one of the readings is more than a point and a half off, I consider it an anomaly and take another to double check. I have notebooks full of every Rockwell reading ever taken in my shop and they all eventually end up in a spread sheet. Really thick blades made from water hardening steel makes me pace and sweat like a caged animal because they offer no reliably accurate place to take a reading and I start to suffer from a data withdrawal.
 
You know, that actually kind'a sounds like fun. Imagine what it would be like with one of those old heterogeneous Viking Age swords? Hoooorah!

Doug
 
Hey guys, well Saturday night I used the old coal fire forge and HT'ed 4 blades, I let them cool out side to ambient temp. i placed them in the bottom of a small igloo cooler, used 3 pints of isopropal 91% and 3 lbs of dry ice. AT first as i was placing ice chunks into the alcohol it was bubbling like crazy. So i carefully dumped the rest of the ice in and left the lid up for a few minutes while i cleaned up my forge and quench oil mess. when i came back most of the fast bubbling was done, and the consistency of the alcohol was like pudding. So i left the blades in there for about a hour and a half. removed the blades, i let them come up to room temp, cleaned them off a bit, then into a 400* oven for about an hour and a half. i decided to take 1 blade and temper again at 425* just to see if i can tell a difference.
so i haven't put an edge on any of them yet.
Also, I want to meet up with Ausbrooks at some point and have him HT a blade for me under a more controlled environment and see how much better a kiln is for HT.
 
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