Analysis of the 5 hour O-1

Kevin R. Cashen said:
Very thin edges that plunge below Ms out of synch with thick spines will ribbon up from the differnential expansion. I avoid these problems with the marquenching process, allowing things to equalize right before complete hardening.
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I have a couple of 2 inch wide, O-1, 3/16" thick blades. Flat grind goes from the spine and edge ground to 0.05". I wanted to cover spine in clay to have differential quenching(in Tough Quench preheated oil)
Now I realize that thick blade and thin edge will have different expansion rates and it might warp. I guess I stay with hard spine unless you can recommend something else to me.

Thanks,
Alex
 
Kevin R. Cashen said:
It is even harder on you if you are hand sanding;) Folks ask why I go so fine before heat treating, my answer- there is a huge difference in hand sanding O1 at 25-30HRC from doing it when it is 62HRC!:eek:
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If you're trying to make me wish I had salt baths, it's working. :D
 
alexmin said:
I have a couple of 2 inch wide, O-1, 3/16" thick blades. Flat grind goes from the spine and edge ground to 0.05". I wanted to cover spine in clay to have differential quenching(in Tough Quench preheated oil)
Now I realize that thick blade and thin edge will have different expansion rates and it might warp. I guess I stay with hard spine unless you can recommend something else to me.

Thanks,
Alex
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yes that is much more complicated, putting clay on the blade will generally spin things off into a very different tangent. Many never account for this, and it creates problems. Many times I have recommended a particular heat treatment based upon what the vast majority of heat treaters do, only to have the poor fellow return to me with opposing results because he failed to tell me he had clay on the blade.

O1 would be one of the last simple steels I would clay, as the clay will offer little resistance to the hardening effect in this steel. When we do use clay we can hope that the quench will be timed well enough to allow the spine to transform at around 1000F into pearlite slightly ahead of the edge transforming to martensite. If we want the Japanese induced curvature thing, we will want more seperation of the two points in order for the edge to out-push the spine. If we would just like things to stay straight we would want to equalize things as much as possible in order for the changes to sychronize.

O1 is going to want to harden to some extent all the way to the spine anyhow, so my suggestion, if you really want the visuals of a hamon, would be to choose a shallower hardening steel. If you are going for strength or toughness, martensite tempered back to the desired level will beat pearlite in both areas, so I would recommend hardening the spine and then torching it back until it is as soft as you like. That's right, I did say torch:D! Under the right cirumstances een I would use torches for some steps of heat treatment;) .
 
Kevin,

you just saved me at least two knives and a lot of frustration.
Can't tell you how much I appreciate it!

Thanks,
Alex
 
Alex, that is good to hear, because the clay thing is so far removed from many of the industrial specs that those answers cannot be found directly in the books. I would hate to give the impression that I work entirely off the theoretical and textbooks, I also balance it with 25 years of gritty bladesmithing experience, I didn't crack my first metallurgical book until I had been bumping around in the dark on my own for 15 years, then it all started to make sense. The books can give you the changes that are occurring in a blade with clay on it, but they can't explain when and why until you have watched the blade move around under the quench and put it all together.
 
Guys,
since you talking about marquench...
How do I learn to recognize that my O1 blade is about 350 F and I should remove it from oil to cool in still air?

Thanks,
Alex
 
Darrel, you are a moderator, perhaps you could do me favor. The time alotted for me to edit my initial post has expired and I would really like to have the following words of that post in bold if I could:

"I must stress once again that I am not in any way advocating soaking O1 for this outrageous amount of time"***

We would be doing a great disservice to all if the impression was given that anybody present thinks that soaking any steel for 5 hours could be beneficial, this was an extreme test by Phillip to push the limits on a process. All we need is one more whacky and extreme heat treat being pushed as an improvement over the practical, sound methods.

The books say 10 to 30 minutes, all of my experience has shown me that I can trust the books on this one.

***Oops! Never mind I was doing things wrong, I did still have time to edit and have done so. Thanks anyhow.
 
alexmin said:
Guys,
since you talking about marquench...
How do I learn to recognize that my O1 blade is about 350 F and I should remove it from oil to cool in still air?

Thanks,
Alex
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Shoot for 400F-425F, just above Ms (martensite start) is best. The oil can tell you a bit, since most oils have vapor points arouns this range, if you pull the blade out and it has a light coating of oil that is giving off some smoke, it should be pretty good. If the oil quickly evaporates, and it really smokes a lot you are probably on the high side.

Do some practice runs. Get some thin stock of the steel you want to use and quench it, put gloves on before hand, then count off as you quench. Interrupt and grab the steel with your gloved hands and see how easy it is to move. If you are above Ms the steel will bend very easily and you will then notice that as it cools the steel will get progressively stiffer.

Anther tool to practice with is our old friend the magnet. If we have completely nailed the quench down to Ms, the magnet will not stick to it until enough martensite has transformed for it to do so.

Of course there is the old "ouch" test that so many get talked into trying at least once, to the endless amusement of others;) , if you touch the blade with bare fingers and you end up with scorched skin and blisters- IT WAS TOO HOT! If you can easily grab it with little discomfort- it was too cold. If you touch and it instantly makes you wnat to say "OUCH!" but that is the extent of it- it was probably about right:D , but I recommend some of the other methods to practice;) .
 
So long as the oil is below 400-425, what is the problem with just sitting the blade in it until it equalizes with the quench temp. Is there any difference between pulling it at 350 degrees and letting it air cool down to hand-holdable prior to temper and just letting it sit in the oil until the same point?
 
Kevin,

do you know if Tough Quench Oil behaves like you said?
Flash point is 355° F. (179.4° C.); Fire point is 410° F. (210° C.).

Alex
 
TikTock said:
So long as the oil is below 400-425, what is the problem with just sitting the blade in it until it equalizes with the quench temp. Is there any difference between pulling it at 350 degrees and letting it air cool down to hand-holdable prior to temper and just letting it sit in the oil until the same point?
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There are a couple of differences, but to most they would be small enough not to get worked up about. First is the distortion due to differential expansion as thinner sections cool quicker, thus forming martensite, faster. It is more critical in more complex shapes that knives, and is the reason that many knifemakers have done just fine cooling all the way down in one shot. But if one does get distortion some gentle guidence with your gloved hands on the way down can put things back on the straight and narrow.

The other difference, there are no doubt others I am not thinking of right now, is what has been called an auto-tempering effect. If you get 40% martensite formation above 350F or 375F then the slow air cooling will allow the temperature of the blade to imediately get a head start on the tempering process with that existing martensite. Kind of like snap tempering and quenching all in one shot. This allows you to take steels like O1 all the way to cold before tempering without worrying about it distortion or cracking.
 
alexmin said:
Kevin,

do you know if Tough Quench Oil behaves like you said?
Flash point is 355° F. (179.4° C.); Fire point is 410° F. (210° C.).

Alex
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That is where you will need to practice. I got an unpleasant surprise the first time I used Park AAA. I had been using another quenchant for years and got quite used to counting off a given ammount of seconds and then interrupting and taking it in gloved hands.

AAA has a startling ability to quench very fast from your austenitizing temp down below 850F and then things cool differently. I counted off my standard seconds and then unkowingly took a 700 degree blade into my gloved hands- but not for long:o ! A good oil will do exactly that, cool very quickly through the upper temperatures and then take things much more gently to room temp. I have little experience with Tough Quench, but I am sure my count would be off the first couple times I used it after AAA.
 
Kevin, (or anyone else who knows) where can I get data sheets for #50 and AAA oils? I've looked on heatbaths website and even checked Google and can't find anything.
 
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