# Trials and tribulations with O1



## SpikeC (Feb 5, 2012)

My last few O1 blades have developed a bit of a curve after heat treat. The first time this happened I was able to grind them straight. The one I just did I clamped straight in the temper stage, but there was still a bit of curve so I tried to bend it back and the tang snapped off! 
I have a light weight jig that holds the blade vertical in the oven and heat soak at 1475º f. for 5 minutes, quench in fast quench oil followed by 30 minutes at -100º f., then 2 2 hour tempers at 340º. This routine has been working really well until now. 
The steel is from Starrett through McMaster-Carr. 
Does anyone have any suggestions?


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## tk59 (Feb 5, 2012)

Are you doing any pre-HT grinding?


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## SpikeC (Feb 5, 2012)

Nope. Just doing the profile.


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## WillC (Feb 6, 2012)

Spike, I've generally forged the taper in on my blades but I always heat cycle before heat treatment. Would still do this on ground annealed stock out of suspicion. 
I will heat to critical and straighten. Heat just beyond critical and check for straightness as it cools, re-straighten as necessary. I will do this 3 times minimum or until it stays dead straight on cooling. Then go to the final heat and soak at critical for the quench. I rarely get one that still wants to kink after that. I use a jig on tempering to straighten as a last resort but not on heat treatment. In my experience with distortion clamping while heating and cooling is best avoided. At least until it becomes necessary.


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## Dave Martell (Feb 6, 2012)

WillC said:


> ......but I always heat cycle before heat treatment. Would still do this on ground annealed stock out of suspicion.
> I will heat to critical and straighten. Heat just beyond critical and check for straightness as it cools, re-straighten as necessary. I will do this 3 times minimum or until it stays dead straight on cooling. Then go to the final heat and soak at critical for the quench. I rarely get one that still wants to kink after that.




My heat treat company does this for my O-1 blanks each and every time just to avoid issues after the final HT. They need/use 3 cycles for O-1


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## SpikeC (Feb 6, 2012)

Thanks guys, and thanks to Marko for his pm which I cannot reply to as his mailbox is full!


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## Mike Davis (Feb 10, 2012)

One thing i can suggest is fast oil is not good for O-1. You need a slow oil for it, you might be creating stress fractures in the matrix by creating undue stress in the blade when using fast oil. O-1 quenches about as slow as it gets...Almost air hardening lol. Maybe Del will jump in, he uses primarily O-1.


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## jmforge (Feb 15, 2012)

Also, you should be soaking O1 for more like 20 minutes, not 5.


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## SpikeC (Feb 15, 2012)

I got my procedure from Devin. He uses a lot of O1, and I trust his advice.


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## jmforge (Feb 16, 2012)

That piece of advice did not come from me but from Kevin Cashen. I did not intend to imply any kind of personal expertise with O1.


SpikeC said:


> I got my procedure from Devin. He uses a lot of O1, and I trust his advice.


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## SpikeC (Feb 16, 2012)

Soak time when heat treating is dependent on thickness. One half hour at 1 inch equals 2.8 minutes.


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## Mike (Feb 16, 2012)

******* said:


> That piece of advice did not come from me but from Kevin Cashen. I did not intend to imply any kind of personal expertise with O1.



JM, I have tried a few methods for O1 and ultimately settled on Mr. Cashen's method. I've tested 6 blades to destruction on three different methods and the ones that resulted from Mr. Cashen's were tougher and their edges held up better. I don't want to enter a urine inspired contest, but this method has worked for me.


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## Mike (Feb 16, 2012)

Just some fun reading material... 

http://www.bladeforums.com/forums/printthread.php?t=394824&pp=20&page=1

http://www.bladeforums.com/forums/showthread.php/398842-Analysis-of-the-5-hour-O-1


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## JMJones (Feb 16, 2012)

Most industry reccomended heat treat data regarding soak time that I have read states something like" Soak for xxx minutes or xxx minutes per inch of thickness" The first number is the minimum time to soak and the additional time is for thick materials. I dont think it is linear so that if it says i hour per inch that it only needs to soak for 15 minutes for a 1/4 inch. I could be wrong though.


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## jmforge (Feb 17, 2012)

True, but a lot of the industry heat treat specs are not intended for knives. With O1, that is supposedly not as much of a problem because O1 is used for cutting applications. On the other hand, 52100 heat treated as intended will work great for bearings which require a LOT of abrasion resistance, but maybe not so good for a super fine edge like you might get from dropping the austenizing temperature down to lower end of the range at 1475. Look at what Bob Dozier did with D2. Another great example is W2. if you look at what the industry specs are for a 1 inch piece, you had better be looking for a tool with a very hard outer skin and a fairly "soft" center even when quenched in water. That is not what you get when you harden a kitchen knife blade that is less than 1/10 the thickness of the test block. Thin sections like knife blades can be quenched in fast oil and some folks even manage to do it in 11 second oil or even canola.


JMJones said:


> Most industry reccomended heat treat data regarding soak time that I have read states something like" Soak for xxx minutes or xxx minutes per inch of thickness" The first number is the minimum time to soak and the additional time is for thick materials. I dont think it is linear so that if it says i hour per inch that it only needs to soak for 15 minutes for a 1/4 inch. I could be wrong though.


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## Eamon Burke (Feb 17, 2012)

It would probably be so complex to quantify the time required that it wouldn't be worth the effort.

The heat being transferred from the air to the steel is not going to happen the same rate at heat from outside of steel to the inside, and a change in thickness from 1" to .1" is going to mean a whopping shift in surface area relative to volume.

I would imagine that Cashen's method is practiced more on thicker blades, and intended to create edges that are great for daily abuse, and Thomas' would be optimized for thinner kitchen blades and creating kitchen-friendly qualities. So in this case, it's Potato-Tomato.


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## jmforge (Feb 17, 2012)

Actually, Cashen austenizes and quenches his blades in salt, but he has coached folks on how to do it in an oven. The soak that he recommends is timed AFTER the temperature in the salt pot or oven has stabilized, which I think assumes that the piece had fully come up to temperature. The purpose is to get everything as fully into solution as possible. In the case if the 52100 at 1475, as best as I can tell, the purpose is to get ONLY that amount of the elements into solution as you desire.


BurkeCutlery said:


> It would probably be so complex to quantify the time required that it wouldn't be worth the eff
> The heat being transferred from the air to the steel is not going to happen the same rate at heat from outside of steel to the inside, and a change in thickness from 1" to .1" is going to mean a whopping shift in surface area relative to volume.
> 
> I would imagine that Cashen's method is practiced more on thicker blades, and intended to create edges that are great for daily abuse, and Thomas' would be optimized for thinner kitchen blades and creating kitchen-friendly qualities. So in this case, it's Potato-Tomato.


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## Marko Tsourkan (Feb 19, 2012)

Higher austenitizing temperature = larger grain size, lesser edge stability but better wear resistance

Lower austenitizing temperature = smaller grain size, greater edge stability but less wear resistance. 

There is an inverse relationship between edge stability (resistance to chipping) and wear resistance (resistance to abrasion). 

Every maker tends to settle in a range of temps that produce desired result (i.e. a balance between edge stability and wear resistance) and they are different from a maker to a maker. Even if it's coming from K. Cashen, I would not call 1475F austenitizing temperature a holy grain of heat treating 52100. 

Kitchen knives are different from all other knives made from 52100 (they are ground differently, heat treated differently, and evaluated differently) and one has to keep that in mind. 

M

PS: I second following Devin's advice heat treating steel.


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## jmforge (Feb 19, 2012)

The "Cashen" method of HT with 52100, which is salt austenizing at 1475 and quenching in oil,(back to low temp salts for tempering, I think) allegedly results in an as quenched hardness of up to 67, very little if any retained austenite and the fine grain structure and small precipitated carbines that you look for in a kitchen knife. If you know Kevin, you would be inclined to say that he probably spent WAY too much time working with 52100 strictly for the purpose of debunking much is what he considered to be hype and heat treat voodoo surrounding 52100. With that said he is still probably inclined to recommend O1 if you want something that is design for slicing as opposed to hard use that has better edge retention. I have talked with Kevin about those two steels in particular and he said that where 52100 can get interesting is when you start playing around with controlling how much of the elements go into solution in order to make it tougher than just the small grain size in the matrix will do for you as opposed to using steels like A2 and L6 that, as he says, give you toughness as a result of their basic chemistry and you take what they give you. I was asking him about steel to use for mid-tech or semproduction knives and he recommend O1 for smaller slicing knives and maybe 52100 for larger blades, which is opposite of what I thought he would tell me considering that 52100 is known for its fine, stable edge, and he has helped guys like Ian Allen-Rowlinson and some other European guys with HT recipes for O1 cutting competition knives.


Marko Tsourkan said:


> Higher austenitizing temperature = larger grain size, lesser edge stability but better wear resistance
> 
> Lower austenitizing temperature = smaller grain size, greater edge stability but less wear resistance.
> 
> ...


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## Marko Tsourkan (Feb 19, 2012)

Not many people use salt baths (I am not yet), and using my Evenheat oven will not give me 67RC (if your steel will even harden to 67, some only harden to 65RC at full hardness) at 1475F +/-10F. I have had good results on edge stability and excellent result on wear resistant austenitizing at higher temperatures. Hell, that knife went for a month in a pro kitchen without sharpening, just hand stropping, but felt a little more like stainless steel on the stones. 

So, it is all relative. One can tweak austenitizing temperature, tempering temperature and do a number of other things in heat treatment to get a desired effect. 

There is no wodoo around 52100. It simply that different combination of temps give you different results. If you use your knives and sharpen your knives you should have a good idea about your heat treatment. You can always send your knives to folks in pro kitchen or here on the forum for a feedback on your heat treatment. 

It's good to get some guidance from experts, but ultimately, you will be making calls, as no settings are the same - we can have same equipment but result might not be identical.

M


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