Quenching ???

[Will Leavitt]

Okay, I've been using OCT 5160 and some new 1084. I used the traditional ATF at aprox 130 degrees. I decided to experiment and used some conola oil at room temp to edge quench a wharney EDC pattern I'm playing with. WOW, I got 60 cuts in cardboard and it still shaves. This is my best performing blade yet.

My question is why would a semi cool oil seem to make a better blade than the traditional warm ATF quench? I'm going to see if I was just lucky or I can repeat this.

Thanks,
Will

[Jamey Saunders]

This is just a wild guess: The cooler oil removes the heat from the blade much faster than a warm oil. The thinner canola also contributes to the removal of heat. The faster you remove the heat, the harder the steel. But there's a point where the steel will crack if you remove the heat too fast. That's why water quenches are so risky. The warm ATF is insurance against hearing your brand new blade go *TINK*.

Someone correct me if I'm wrong. It's midnight, and I'm still at work, so I'm just spouting off at the mouth.

Warning: The above was written by a total idiot, who has been overworked and deprived of sleep for the better part of three months. Take the above information with a grain of salt.

[Ed Caffrey]

There COULD be a lot of factors that came into play here.......... One of them is not the issue of the oil temp. by that I mean that the cool oil does not qench at a faster rate than a warm oil. To explain...... an oil that is cool does not circulate nearly as well as a warm oil....and often times a cool/cold oil type quench media will develop a vapor pocket immediately surrounding the blade, which acts as a themal trap to hold in the heat, and actually reduces the speed at which the media cools the steel. Warmer oil will circulate freely, and if you pay close attention to the currents and eddys that are created in both a "cold" oil qench versus a "warm" oil quench when you quench a blade, it will be obvious.
It may be something to do with viscocity between the different types of oils at given temps, but there again, I doubt it. ATF is generally considers about the fastest "routine" type of quench media as far as the "oils" go.
My bet is that there is some other variable in the equation that may not have occurred with previous quenches, and without knowing the specifics, my guess is that the time/temp curve was nailed for the blade that is cutting so well for you...........and may have been slightly off on others that may have not measured up the your latest blade.

[Tom Ferry]

Will,
There are alot of variables involved in hardening a blade. Not only will different oils with different viscousity give different results but the temps of the oil and the temp of the blade going into the quench can all play a role in final hardness.
As Ed stated a warm or hot oil will quench or cool the blade faster than a cold oil. Although there are some manufactured quenchants that are used at room temp.
Bringing a blade to non magnetic to quench is just a guideline. A blade can still harden below non magnetic if the conditions are right, such as the quenchant. A blade can also not harden completly if it is to far above non magnetic with the wrong quenchant. I guess what I am saying is that you can usually make any quenchant work properly. The trick is playing with it enough to understand how that particular quench responds and what temps you need to apply to achieve the greatest results.

Sounds to me like you nailed the hardening process with the canola oil.

[fitzo]

The comment stated in the heat treating books regarding using heated oil suggests that the main purpose in heating the oil is specifically to reduce viscosity to get a faster quench. The reason is exactly as Ed stated: reduced viscosity has a lower surface tension and penetrates the billions of bubbles that form as the oil heats to the temperature of the hot steel. They can flow away from the blade easier, like bubbles travel easier through water than molasses. As long as the steel is boiling the oil, the vapor barrier forms. This superheats and causes a loss of heat transfer. The vapor barrier has to be "removed" to continue a rapid heat removal. I think that if this vapor barrier didn't form, and mixing could be maintained, that cool oil would actually remove heat faster, just as an ice cube placed in a drink cools it a lot faster than if you put it in the 'fridge.

There are a couple ways to do this:

1) Swish it around in the oil. A BAD IDEA: the blade will warp.
2) Reduce the viscosity of the oil so it can flow more freely, penetrate the vapor barrier easier. This is one of the most important characteristics of "designed" commercial heat treat quenchants.
3) Introduce a mild mechanical agitation to the oil, something commonly done in industry.

Vegetable oils are usually a mixture of many different types of oils from the same source: seldom does one plant produce only a single chemically unique oil. These oils thus have a substantial variation in composition based on the genetic of the seeds and their growing conditions. The point here is that you may have a batch of oil that is lower in viscosity, and removed the heat handily without "vapor barrier" problems due to the temp.

Sorry for the longwinded add-on to the already sufficient explanations Ed and Tom gave.

[Will Leavitt]

One thing I did differently while quenching this (and subsequent blades) is that I initially plunged a little farther up the blade than I normally do then moved the blade up and down never going any further than 1/3 of the blade width. Maybe this "agitation" helped. I'm pretty happy with this but I'm going to do an ATF quench "agitating" the blade up and down in the same manner.

Thanks for the help guys.

[whv]

the real science in heat treating, or anything else imho, is to reduce the number of variables to zero (or one if you are experimenting).
will had three variables going here: type of oil, temp and agitation method. to find out which was more significant of the three, just change one at a time

[DaQo'tah]

Will Leavitt...

Hi my name is Daqo'tah.

I am also into making knives out of 5160 (forged from John deere load shafts ), and I am very interested in any help you might be able give me on making my blades cut better...

Right now I quench in Texaco type A quenching oil,,,I use a O/A torch to heat the cutting edge to non-magnetic...I dip the point in first , waite to the count of 7, then lower the rest of the cutting edge on to the little table that sits in the quenching oil.

I try to do 2 or 3 quenches, then 2 Temperings in a kitchen oven set at 330.


any place you guys see for a change in my systems?

[John Frankl]

Yes, but that is not to criticize Ed Fowler's method. I've seen him count to 7 on that video, and I cringe every time. But his blades cut and then some, so he is doing it right for his set-up.

OTOH, 7 seconds can be both unnecessary and risky. Once your tip has cooled to a bit under 1,000F, you are good to submerge the rest of the blade. I'm guessing this should take no more than 3 seconds--many nail it in 1 second for 1095 and such. I'm not sure about all the other variables in your shop, but if you wait too long, like 7 seconds or anything over that, you will not get near full martensite conversion/hardness. My books are still in boxes, but I'm guessing 5160 won't give you much more than 4-5 seconds to miss the pearlite nose (i.e. get down to under 1,000F or so), so waiting 7 seconds may be risky.

Ed, I know you do a lot of 52100 and some 5160 with a torch, how long do you wait when edge quenching?

John

[DaQo'tah]

well...i could change to a 3 second count,,,but is 3 seconds enough time for the point to cool down enough when Im never that sure at it's starting temp?


also,,,,when i rock the rest of the blade down into the oil, the point will slightly rock out of the oil...Im not sure that just 3 secondsin the full oil , then lift out of the oil is enough sometimes...


I have been told that the oil is quenching fully just the lower ,deeper, sections and that the upper oil (Like the top 1/8 inch) is not doing much quenching.

right now i try to quench as fast as I can, I go from the torch to the point diped into the oil, bang-bang.

I have been watching the rest of the blade as the point is dipped into the oil first, and the rest of the blade sure seems the same red hot after just 7 seconds.

as an experiment, I will go half way and do a 5 second count on a few blades, and see if I like the results..