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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 06-27-2008, 02:46 AM
gavinphillips gavinphillips is offline
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Tempering in heated oil, with deep-fat fryer?

I understand you can temper by immersing in hot oil. I propose to get my domestic deep-fat fryer, fill with cooking oil, and plunge the blade in. I use O1 steel.

I imagine this will be quicker than using the oven in the kitchen to do the tempering.

Here is the fryer:


and, next to the tape, an example of the type of tool that I wish to temper the last inch or inch and a half of:


Has any one tried this?
For how long do you suggest I plunge the blade into the hot oil?
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  #2  
Old 06-27-2008, 04:28 AM
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Robert Mayo Robert Mayo is offline
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No it will not be quicker you still have to temper O1 around 400 degrees for min. 1 hr. so regardless of what you use to temper it still has to be at that temp for min. 1 hr. and 2 hr is better. Allso at 400 degrees you are getting close to the flash point of your oil,
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Old 06-27-2008, 07:29 AM
Kevin R. Cashen Kevin R. Cashen is offline
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gavinphilips, I need to clarify when you say "temper" that you mean actual tempering, as in the heating of a hardened blade around the 400-450F range in order to reduce brittleness? If that is the case then yes you can use that setup for very nice tempering. However if you mean the very common, yet very incorrect usage of tempering to refer to hardening as well, then no I would strongly advise against it, even with a steel like O1. I would still quench into a typical 130F oil for quenching and then temper in the hot oil, unless you have one of the oils engineered and designed specifically for martempering. You will get people who will tell you to quench and temper in the same hot vegetable oil but they really are not in posession of all the pertinent facts and saftey considerations, in my opinion their caution and reason has been compromised by their frugality.

Used just for tempering, liquid mediums will transfer the heat into the blade faster than air so while I agree with Robert that you will still need that hour, more of that time can be spent actually at temperature with the tempering process at work than it would with an oven. Also the liquid will tend to even out the heating, giving you a more uniform temper.
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Old 06-27-2008, 09:03 AM
AcridSaint AcridSaint is offline
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Bob Warner talked about trying this a few years ago with peanut oil and a turkey fryer. Don't know if he ever got around to it though. I always thought it was a good idea.


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  #5  
Old 06-27-2008, 09:39 AM
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NJStricker NJStricker is offline
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Following up on Kevin's statement, if you are referring to the quench in oil to harden the blade, it looks to me from your pic that you have a relatively low volume of oil. That might be fine for quenching 1, maybe 2 blades in short succession. If you plan to do a larger batch of blades you will likely need to wait a while to give the oil time to cool back down to the 130-170F range. Use a thermometer to verify your oil temperature and make sure that it stabilizes. Some of those electric deep fryers can be pretty erratic because of the simple thermostats in them.
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Old 06-27-2008, 10:46 AM
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chiger chiger is offline
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Gavin,

The guys are steering you straight. You can use your little fryer to quench or temper that small tool in the pic. That should be plenty of oil to quench a tool that small. I would, however suggest that you move the operation outdoors for safety. Different common cooking oils have different flash points and a flash fire and flare up is a REAL possibility during quenching.

For tempering, a hot liquid tempering media, like oil in a cooker is a great way to go. As the guys have stated, the oil will not change temperature as quickly as the air in an oven making it extremely efficient as a tempering medium. Tempering times/temps are tempering times/temps, however. It will not reduce the time or temperature requirements for your tool.

Do some checking before you choose your cooking oil. You need to use oil that has the highest flash point. Not just to avoid fire, but because at 400-450 degrees oils with low flash points will produce a lot of smoke whether you can see it or not. It'll cover everything in the shop! Doooough! ;~0

Before you know it, every free floating thing in the shop will be hanging from the ceiling. ;~(

chiger,
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Old 06-27-2008, 03:31 PM
Doug Lester Doug Lester is offline
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I use vegetable oil in a turkey frier and it works fine for hardening. My kettle holds over three gallons of oil which I bring up to heat, about 120-130 degrees, on top of the stove. There's a large enough mass of oil to hold temperature long enough for me to heat the blades and quench. Also that much oil can hold a lot of heat so I can do a few blades without any significant change in temperature. It is also deep enough to harden a 7" blade but that's without getting all the tang down into the oil, which is not big deal.

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  #8  
Old 07-01-2008, 03:50 AM
gavinphillips gavinphillips is offline
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Given the fire risks, I think I will stick to oven tempering in the kitchen oven and NOT use the turkey frier.

I do intend to do larger batches of blades ( at least 10 or 20 at a time).

Thanks for these replies!
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  #9  
Old 05-24-2018, 08:59 AM
WilliamHans WilliamHans is offline
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