How long under the oil

Britt_Askew

Britt_Askew

Knifemaker / Craftsman / Service Provider
Joined
Dec 9, 2010
Messages
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I want to do my own side by side testing to see what I like best. I started with 1095 and parks50 but now I have got me some canola and some 11 sec quench and some 1084,1095,O-1,5160,cpm3v,cpm35,cpm154.
My question is for the 1084,1095,O-1,and 5160 steels ..... how long do I keep them submerged under the oil when quenching ?
 
Definitely long enough until you're under the "pearlite nose". (TTT Diagram)
 
Troop said:
Definitely long enough until you're under the "pearlite nose". (TTT Diagram)
Click to expand...

No, you need to be past the Martensitic start point (Ms) at 400F on the TTT.

If doing side-by-side comparison tests, I would submerse all blades until they equalized to the tank temperature ( around 120-130F), which is cool enough to touch.
 
I read the link you posted and what I gather from it is that to try and maximize martensite formation by extending the cooling from the Ms line 400F to 150F over a 15 minute span? Is this what is recommended or that most do to get maximum hardness from 1084?
 
Yes, that is what I was trying to get across, but in no way do I want to step on Stacy's toes. He is more knowledgeable than I when it comes to metallurgy. I have found that air-cooling from Ms seems to produce less stress during the martensite transformation period. I get less warping, and it may (not 100% positive) result in a blade with less of a chance of fractures in the structure, because of the reduced stress.
I don't know if this practice is "recommended", but this is what I do quite frequently. I don't think this method will produce a harder blade, but may result in better edge stability due to less stress during the martensite transformation stage. The less stress during this period, the better. Look at why people snap temper before cryo. When you go straight into cryo, after the blade reaches ambient, you're adding more stress to an already stressful condition. I've had two blades peel in half lengthwise going right from ambient into the cryo (sub-zero actually). It was later determined that there was a defect in the steel, but it still shows the point.
 
Is there any merit to the link Troop posted as oppesed to leaving it in the oil till its at the oil's temp for 1084?
 
I think what he's doing in the link is a variation of the Martemper. Quick quench to get under the pearlite nose, slow martensitic transformation.

Some things I'm not overly familiar with though. He is quenching while the blade is cooling slightly, after it has gotten to 'critical', but before dropping off to 1333 degrees F - this is an idea I've never heard of or read. He's also using brine even for O1, which has a 2 second window to get under the pearlite nose; I'm not sure why he doesn't use an oil?

I've always been curious with the info in that link, but never got answers. Hopefully someone more versed can chime in and clarify.
 
Troop,
I understand what you are saying, but the OP question was for side by side testing of different steels. To eliminate as many variables as possible, the cooling rate should be the same for all samples.

In doing the HT on a knife blade, the cooling rate must be fast enough to miss the pearlite nose at 1000F, and then gentle enough to drop smoothly to the Martensitic start point. This can be done fairly rapidly for most oil and water hardening blade steels and thickness. If you delay it too long, some of the supersaturated austenite ( That is what you have between the pearlite nose and the Ms), can stabilize, or go into a structure called bainite, which has some of the features of pearlite and austenite. Bainite is not as hard as martensite, but it is much tougher.

From the Ms to the Mf, the range when the steel converts to hard martensite, the cooling needs to be a bit slower and as even as possible. The rate of cooling in this range varies somewhat depending on the steel type, but for most common blade steels, this is best left to the cooling rate of the oil. That is one good reason to use professionally engineered quenchants, as these features are built into them.

Letting the steel cool as slowly as possible ( air cool) sounds like it would be a good way to avoid any stress, but too slow can have its hazards in some steels. The warm oil will allow a gradual drop from 400F to 130F at a suitable rate for almost any knife blade. Some steels have hours between Ms and Mf, but that would not benefit the blade over an ambient air quench or quench plates.

In reading the TTT charts the times shown are the maximum for each transition.....not the optimum.
 
"From the Ms to the Mf, the range when the steel converts to hard martensite, the cooling needs to be a bit slower and as even as possible. The rate of cooling in this range varies somewhat depending on the steel type, but for most common blade steels, this is best left to the cooling rate of the oil. That is one good reason to use professionally engineered quenchants, as these features are built into them." Stacy

CANOLA:

* Faster quench rates in the 1300 -1100 F temp., range, where high quench rates are necessary to achieve properties.

* Slower quench rates at low (900-250 F) where low rates are desirable to minimize distortion.

Reference:

http://books.google.com/books?id=io...&resnum=1&ved=0CBMQ6AEwAA#v=onepage&q&f=false

One of the main differences between petroleum oils and vegetables oils, is that the petroleum based oils need cooling rate accelerators for the higher temp., ranges of the quench for difficult to harden steels,… whereas the vegetable oils generally don’t, due their inherent lack of a vapor jacket phase.

Both types of oils rely on convective heat transfer at lower temps.

Note: The term "Mineral oil" includes petroleum based oils and usually is.
(Just a note to help clarify the text in the reference in the paragraph above sightings.)
 
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Tai , You are probably the one most responsible for me purchasing a bottle of canola oil :)

The only thing I am interested in is using the oil that will give me the best results, dont much care what its called. I will post my results when done.
 
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