What is the Best Oil for Quenching Knife Steel?
If you ever get into making your own knives or tools, at some point you will need to quench a knife. Most commonly this is done with various types of oils. But what is the best oil for quenching steel?
First, we need to understand what is the purpose of quenching and what it does to steel. Quenching is our case is when we heat a high carbon knife blade to a high temperature and quickly cool it. This quick cooling process hardens the steel. If we didn’t do this the steel would be too soft to make a good knife. Hardening allows for better wear and edge retention.
Here are some common oils used as a steel quenchant:
Food Grade Quenching Oils
Food grade oils are commonly used as a quenching oil for a few reasons. First, they are much cheaper than commercial quenching oils. Second, they are readily available. You can go to your local Walmart and purchase these oils for $30 - $40 for our purposes.
These food grade oils also tend to smell better when quenching and tempering. This can be important when doing either of these processes in an enclosed area or in your house.
The two most common food grade oils used in this process are peanut and canola oil. Both of these oils have high flash points which is good for the quenching process. You will need to preheat these oils to slightly higher temperatures when compared to commercial quenching oils (120 - 130 degrees Fahrenheit).
Motor oil is a common oil used in the hobby knife making industry. Both used and new motor oil is used in this process. It has some advantages and disadvantages.
One advantage is new motor oil is cheaper than commercial quenchants. Used oil is obviously free. Also new and used motor oils are available everywhere. Chances are you have some in your shop or garage right now.
Disadvantages include motor oils contain additives and potential toxins. Another disadvantage to motor oil is that it stinks during the quenching process. This can be a problem if you are doing this in an enclosed area or in your basement. I suggest not inhaling this either.
These smells can also persist during the tempering process. That’s not a good thing if you are using your wife’s oven for this!
Used motor oil can also leave a black film on your project that is very hard. It can be a pain to remove this later.
Mineral Oil & ATF
Some other common oils include mineral oil and automatic transmission fluid (ATF). These can be alternatives to using motor oil. In the case of mineral oil, it doesn’t have the additives that can be found in motor oil.
Both can be found fairly easily but if you can’t find mineral oil, baby oil will work. It’s basically the same thing but with a tiny bit of perfume added. It will work fine.
Commercial Quenching Oils
There are several commercially available quenching oils on the market. These oils are specifically design for this and have special properties that make them faster or slower quenchants.
Ideally this is what you want to use. However, they can be hard to find and aren’t available at your local Walmart. Also they can be very expensive especially if you have to ship them. They can run around $150 for 5 gallons of oil.
Parks is a common brand that is used as a commercial quench oil. The chart below shows two of their more common oils.
Park Brand Quenching Oils
#50 quenching oil comes close to matching the quench speed of water. However, #50 will give you a less severe and a much more uniform quench that water will.
This is a good quenchant to use with 1095 high carbon steel.
AAA quenching oil is the most popular and widely used quenchant offered by Park. This oil provides a uniform cooling rate and a cleanable surface if maintained.
This is a good quenchant with something like a 1084 carbon steel.
Additional Things to Consider when Quenching with Oil
- Always have on the proper safety equipment. Safety glasses, gloves, leathers, etc.
- Always have a fire extinguisher and a bucket of sand on hand for emergency fires.
- Make sure oil is in a metal container. Plastic can melt and cause an accident. Use a turkey fryer for larger projects. A metal container that will hold around 2 gallons is ideal for smaller projects.
- Oil can flash fire when you first place the blade in it. Long pliers or blacksmith tongs work good to get your hands out of the way. Never have your face directly over the oil quenchant container.
- Always heat the oil up prior to quenching your project. Quenchants should be at room temperature or slightly above. Never quench in cold oil. Heat an old bolt or scrap steel and use it to bring the solution up to temp.
As you can see there is lots of different oils that you can use. The best oil for quenching knife steel might just come down to your situation. Availability, price, and personal preference can all come into play here. Personally I use both Park's #50 & Canola Oil.
Also certain carbon steels quench better in certain oils than others. For example a higher carbon steel like 1095 found in my bushcraft knife does better in something like Park #50 oil. This is because it a faster quenching oil. Where something like 1080 carbon steel would be fine in canola oil or Part's AAA.
I may write an article later explaining this in more detail. What is your favorite oil to quench your project knives in?