Can you oil temper rather than oven air temper?

M

MT Borg

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Jun 14, 2007
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I saw on another thread the problems with a toaster oven maintaining, or acquiring true temperatures. Suggested was fire brick in the oven or 1/4" steel for mass to maintain temp and the toaster cycles temps so a good temp probe was needed. And then you needed to watch it. I do not want to use an oven that I eat food from.

Saw a deep fat fryer at Wally World and 400 degrees is a low temp for it and was wondering if say some used (carboned up) automotive oil maintained at 400 would do the same as tempering in an air oven. Am thinking of 1095 steel. Seems that that would be an easier process. Is there something magic in the air?

Thank you for replies.
 
I am not entirely sure, but maybe the term is mar-temper?

At least that was what I read Frank Richtig's secret 1095 treatment used. Molten lead or babbit. I think folks use low temp salts rather than boiling oil though.

Still trying to grasp it. Reading Metalurgy for the non-Metalurgist at the moment.
 
I would hate to think what fumes used motor oil would put out at 400-450 degrees. I'm sure it would not be good. Clean your blade real well with dish soap and water. It will not contaminate your oven at all. Might not be ideal but it has worked for a lot of people.
 
Tempering in oil has been done for generations, and can work quite well...but it
isn't martempering.....that's a whole different process.

The roasting ovens will heat oil well, but as with toaster ovens, they need to be
double checked with an independent thermometer.
 
Cooking oil is often used to temper simple carbon steel among traditional Japanese smiths.
Put hardened (water quenched) blade into heated oil for an hour or so.
Several decades ago, a swordsmith shoooled me forge welding also told me as such.
 
oil shurely can be used but one thing to think about is oil at tempering temps is getting very close to it's flash point how close depends on what oil is used. Why not use low temp salts which could be melted in a fryer and if it had a stainless liner should last a long time.
 
What Mr. Burke said, Deep fryers typically do not operate as high as 400F. As best as I can tell, that is the absolute upper end of the range for the high smoke point oils. 350-375 is more typical.
 
If temperature regulation is the problem, would putting the blade in a dutch oven inside a large oven serve to damp the temperature flux?


If you want to use oil, refined canola is going to get you up to 470 before it starts to smoke - and smoking isn't going to affect anything anyway. Unlike quenching, the behavior and breakdown of the oil isn't going to change how the blade tempers. The oil is just a big heat sink and will continue to be until it is no longer liquid. But canola isn't going to fume your kitchen.

You could make some fries, first. Then drop in you blade. :thumbup:
 
As stated tempering in oil is feasible with proper temp control but don't quench into hot oil. The additional heat introduced by the hot blade could be enough for a big flash fire.
 
I'm not sure what the concern is with tempering a knife in the kitchen oven? I do all the time (with a huge thick cooking stone as heat sink) and I turned out nor-----rrrrrr-----mmma ----nor ---ma----ll. Normal....that's it.
 
samuraistuart said:
I'm not sure what the concern is with tempering a knife in the kitchen oven? I do all the time (with a huge thick cooking stone as heat sink) and I turned out nor-----rrrrrr-----mmma ----nor ---ma----ll. Normal....that's it.
Click to expand...

I was assuming the concern is when using a toaster oven - that the while the average temp is 400, the blade might see higher temps as the oven cycles to maintain heat.
 
The idea of austenizing/marquenching/tempering in a liquid is nothing new. Obviously, a stable liquid at the appropriate temperature is a fantastic idea, for lots of reasons. However...

The problems that result from trying to do it with various oils (mostly flash-points/extreme fire hazards, and horribly toxic fumes) are exactly why liquid salts in precision kilns are used instead. Ever seen one of those videos of someone burning down their entire house trying to deep-fry a turkey at 350 or 400F? Yeah... :eek:

I invite you all to google/youtube an ABS Mastersmith named Kevin Cashen for more info and background on the topic of salt-baths for heat-treating knives.
 
RX-79G said:
I was assuming the concern is when using a toaster oven - that the while the average temp is 400, the blade might see higher temps as the oven cycles to maintain heat.
Click to expand...

I stole the idea from someone here at bladeforums to make a little tinfoil "tent" over my blades in the toaster oven to shield them from the very hot radiant heat when the elements are on. I also put one over the bottom elements so hopefully the blades don't get blasted as badly when the elements are hot as they cycle on and off.
 
For what it is worth, the OP wants to temper 1095 at a fixed 400F and the flash point of used motor oil can apparently be as low as 420F. So think this through before acting; not that a fryer is likely to cause ignition at these temps, but any other additional flame or spark might. Best to move it all outside while remembering all the giant ash piles that used to be garages, shops, etc the day before Thanksgiving.

The OP had concerns about using his kitchen oven for tempering. Just clean the blades well with a stiff brush, hot water and dish detergent between the quench and 1st temper cycle. Clean knife steel does not smoke or fume at tempering temps, and is not so different than the steel oven racks/grates that get heat cycled every day. No worries on that front in my personal opinion.

To me the bigger concern is overtempering, especially the thin edges and points, because of the routine temperature swings and possible radiant heat exposure as elements cycle on and off. On top of that, consumer ovens are poorly calibrated IME. For example, originally our oven’s dial setting of 400F was actually averaging 422F on the center rack (ranged about 410F to 455F over half an hour after preheating).

For me the best solution was to go back to using a 110V toaster oven. The way I use it, it will hold temp within 2 or 3 degrees of the set point all day long. The tricks are to have the means to measure local temperature accurately and precisely, and to shield your steel from radiant heat of the cycling elements.

I simply place a type K thermocouple alongside the edge of my blades and roll them loosely in 5 or 6 layers of regular aluminum foil. Twist the ends tight (around the probe’s lead) but leave the body loose. I run the lead out the front door and leave it hooked to my meter throughout the cycles. This setup insulates the entire piece of steel from rapid temp changes/overshoots and gives great real-time feedback for temperature control. You can also clamp your steel for warp removal and still include thermocouple in an appropriate location for tempering. If ever needed, I just wrap clamps, bars, blade, and TC into a larger bundle.

The difference this made in my work in terms of control and predictable edge performance would be hard to overstate.
 
For this purpose, I don't understand why motor oil would even be considered over canola, both for flashpoint and fumes. People put food oils in their ovens at 450 degrees all the time. There is no real danger.
 
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