Please Critique my O1 Heat Treatment Procedure

B

bobasaurus

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Mar 13, 2013
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I wish to heat treat some small O1 steel folder blades (in a digital kiln), so I've scoured the internet for various methods and tried to come up with the right procedure. Here's my current plan:


initial prep: coat blade in ATP-641 anti-scale coating

preheating: 1250 deg F, keep blade in kiln while warming

hardening: 1500 deg F, hold for 10 minutes

quenching: canola oil at room temperature, agitate rapidly by moving blade up and down (NOT side to side), keep going until bubbles stop and blade is hand warm (about 125 deg F)

tempering: 400 deg F, hold for 2 hours minimum, room air cooling after


Does this seem like a solid plan? Any changes or additions? Thanks for the feedback.




Edit: after reading through your feedback, here is my new plan:

initial prep: coat blade in ATP-641 anti-scale coating

preheating: 1250 deg F, keep blade in kiln while warming

hardening: 1475 deg F, hold for 10-15 minutes

quenching: canola oil warmed to 125 deg F, agitate rapidly by moving blade up and down (NOT side to side), keep going until bubbles stop and blade is hand warm (about 125 deg F)

tempering: 375 deg F, hold for 2 hours minimum then cool with water, repeat for second temper at 375-400 deg F
 
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I heat my canola up to 125-130 degree's to quench in, also it is ok to cool the blades in water between tempering cycles so you don't have to wait until they cool to room temp before putting them back in the oven, but other than that, your process sounds good.

-Adam
 
I've heard about heating the oil, I'll have to try that out. How many tempering cycles would you recommend? I had only planned on one, but I can do more.
 
from what i have heard two seems to be the number popping up a lot but i havent tried o1 yet so im just telling you what ive heard from others
 
There is no need for a second tempering, and as posted before, I would pre heat the oil before hardening. You can put a chunk of steel in the oven along the knife and before hardening dunk the steel in the oil to preheat it.


Pablo
 
O-1 is a hyper eutectoid steel and will benefit from, and I dare say must have, that second temper. Retained Austenite. Also...due to the same concern...I would suggest the austenizing heat be at or under (preferably under) 1500F. Right around 1475F or so is best. We are splitting hairs here, tho. If you have a controlled kiln...I would shoot for a 10-15 minute soak at 1475F. The canola oil should be from room temp to 130F. No higher than that. 150F canola is really too hot. And the initial temper I recommend you start at 375F for one hour. Check and see where you are at after that. If it needs to be softened up a bit...go to 400F for one hour. There should be no reason on low alloy carbon steels to go much beyond one hour per temper cycle. And one temper cycle is not enough. At least two should be employed on ANY "high carbon" steel. There is ZERO reason to use cryo with O1 if heat treated properly so do go down that route either.
 
samuraistuart: Yeah, I hear cryo treatment is more for A2 and similar steels. 1475 sounds good, I only went higher to allow for some temp drop while gripping the knife and transferring to the oil bath, but it should be a quick process. That's a good idea with the tempering, though I'm not sure what a good hardness test would be. Are you sure about the 1 hour tempering? Every source I came across stated a 2 hour minimum.
 
Stuart is right on the 1475. Going higher gets too much carbon into solution, and causes retained austentite. There is no reason to temper O1 to below Rc61 for general use. It's a pretty tough steel, and Rc61/62 is it's sweet spot. Test the edge by chopping into hard things, if you get a chippy edge, go 25f higher each temper until the edge no longer chips.
 
samuraistuart said:
O-1 is a hyper eutectoid steel and will benefit from, and I dare say must have, that second temper.
Click to expand...

Bohler, manufacturer of quality O2 steel (K720) says nothing about a second temper, but it do says the temper must be at least two hours, also it notes that sometimes you can lower the tempering temperature in favor of a longer temper.


Pablo
 
Knifemakers have figured this stuff out. I cannot imagine ANY steel manufacturer, especially one supplying knife steel, recommending only ONE temper. Never heard of that EVER. I have always heard THREE tempers.....which I believe with carbon steel is not necessary. Stainless......yes. Two tempers, at least one hour each (some will even say 45 minutes is all required in a cycle....I go with one hour minimum), is basically required for trying to make the best blade we can. Again.....if you haven't read up on it and are curious as to why.....search "retained austenite".

Lower the temperature in favor of a longer temper? I'm sorry....that is just WRONG. If a you are shooting for a Rockwell of say 59, and everything went perfect in the quench.....O1 will probably need a temper of about 420F or 430F (maybe slightly higher if it was real hard after quench). So in that situation....I would run one temper at 375F for one hour. Then another cycle at 420F for an hour or hour and a half. Might even be tempted to go 375 for an hour, 400F for an hour, then 420F for an hour and check.

Back to the "longer lower temper equals a short higher temper". NOPE. If you are shooting for 59.....and you leave the blade in the oven at 375F.....you'll never reach 59 (within a reasonable amount of time...like days....I don't mean decades). You'll reach 62 and it will remain 62 for hours upon hours. Temperature in tempering MUST be hit and soaked.
 
Most recommend two tempers for good reason, it works, and the micrographs show this. Kevin Cashen notes an evening of Rc values across the steel with a third temper. I tried one, two and three tempers, and he is right. Does the third temper make a real world performance difference? I don't know. I do know that I like to do the third as it minimizes the variance in Rc #s. I walk my tempers to the desired hardness, so I typically do three anyway.

Longer temper? Overnight might make the difference of 1/2 Rc point.
 
Check data sheets for "aging" treatments. These are the lower/longer treatments, but they are usually dozens of hours.
 
Okay, I've updated my plan in the original post to reflect your feedback here. It now has 1475 for hardening, warmed quench oil, tempering first at 375, then tempering again at 375-400 depending on hardness desired. Does this seem about right?
 
1475 for 30 minutes after reaching temperature. Quench in warm oil (11 sec should be fine). Cool to -80 to -90 F (dry ice and antifreeze or similar), temper 1 hour @ 360 to 380, quench in water, cool in dry ice solution again, temper again, quench again, and one more for squirts and giggles if desired.
 
The Mf of O1 is still above room temp. So dry ice or cryo will do nothing to benefit O1. HOWEVER....if you DO see performance gains by using cryo treatments with a low alloy steel like O1....you did something wrong in heat treatment. This is a hot button topic.....using cryo for low alloy carbon and tool steels, but I don't see why. O1 has an Mf of about 100F or 150F. The martensite has finished it's transformation at this temperature....and going any colder will do nothing for you. It WILL help if things didn't go right in the first place...or too much carbon in solution, etc. Therefor, I cannot recommend using any cryo procedures for O1 steel....as I see it as a complete waste of time and energy. However, if you are seeing performance gains in your shop....then by all means use it.

Me2 mentioned quenching during the tempering cycles...and that has caused some questions as to why. It really is a time thing more than a performance gain. If you're like me, you do the first temper around 375F or so, and then I like to clean off the scale and decarb for the next round (or two). So quenching it from 375F to room temp helps speed things up. There is even some speculation that quenching in water during tempering might help to precipitate some of the super small carbides that form during tempering....but that is probably not going to be noticed in use. How the knife will be used should determine the final tempering temperature. If it is a kitchen knife that will not see abuse, but rather needs a nice hard long lasting edge, I would say do not go above 400F or so. A 420F temper would make it a bit tougher. If it is a hard use camp knife that will see many chopping tasks, a higher temperature of 420F-450F may be in order. All the way to 500F for a really tough blade (at the expense of edge retention of course).

I would think the McM Carr 11 second oil would be a great oil for O1. Maybe slightly slightly slightly faster than needed...but a good choice methinks.
 
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If you have a tester, or access to one, Austentize a coupon at 1455, 1465, 1475, 1485, and 1495. The one that has the highest Rc value without tempering is the one that got the optimum amount of carbon into solution, and will not require cryo. The lower temps got too little carbon into solution, and the higher temps get too much into solution. In industry, larger carbides (possible by getting more carbon into solution and using heat to break up the existing carbides) can have an improvement in wear resistance in the right application. This is not a good compromise in a blade as we use them. In industry, cryo will deal with any retained austentite. For a blade, we want fine, evenly distributed carbides. I used to thermal cycle only 52100, but I cycle all of my carbon steel now (excepting 15n20- Its in great shape from Aldo to start with.)
 
Interesting. None of my sources show an Mf for O1. Buehler's data sheet shows up to 10% RA when quenched from 1470 F, while still getting a hardness of 65 HRc. A lot of this will be removed by tempering, but part of the quenches after tempering and the cold treatments are to get rid of as much as is possible without changing it to something other than martensite.
 
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I run a hundred grinding clamps, made from 01, at a time and after doing close to 3,000 of them I've found that a 1200 degree stress relief soak in the kiln, for 2 hours, is beneficial. I switched from a fast oil, 9 to 11 second to a med speed oil after experiencing breakage in a small percentage of each run. After making the changes stated above, we have not experienced and breakage in the last 1500 clamps. I am working with 9/32 X 1/2 inch stock which is thicker than knife blades and the same process might not apply. Me2 might clarify this.

Fred
 
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