If you are new to blacksmithing or just curious about the practice, you may have heard of the process of quenching, or submerging your workpiece into a substance to cool and harden it.
Blacksmiths generally use water, oil, or compressed air to quench. These substances vary in environmental impact, cost, and effects on the metal, but the best quenching medium is usually water or quenching oil.
To learn more about what quenching is and which quenching substances are the most effective, keep reading!
How Does Quenching Work?
Quenching is when hot metal pieces are submerged into fluid or air. When workpieces reach the cooling process, quenching is used to quicken the metal’s cooling and increase its hardness.
Check the video below from the tv show “Forged in Fire” for some great tips (PS: I love this show):
After the metal is shaped and soaked, it is submerged into a quenching fluid. When the metal is heated and reaches its correct temperature, it is soaked to maintain its temperature evenly throughout the piece.
Then, when the temperature is consistent, the metal is submerged in the quenching material, forming a vapor layer around the metal.
This quenching process causes the metal’s crystal structure to decrease, making it denser, stronger, and harder.
Why Is Quenching Important?
When steel or cast iron is made and cooled slowly, they form a weak metal.
Cooling these substances more quickly allows a much harder and stronger metal to be formed.
Therefore, by controlling the heat transfer from hot metal, you can ensure your metal is as strong as possible, and improve its microstructure by preventing cracks and flaws.
Without quenching, your metal would not be hard enough to use.
Be sure to check your steel’s rating for quenching before deciding which quenching substance to use. This rating will advise you on which substance works best for your material.
The most common substances used for quenching include water, quenching oil, and air.
Different Types Of Quenching Media
The most popular types of quenching media for blacksmithing are the quench oils (vegetable, motor, mineral), water, and compressed air.
Read below more about each one:
1. Quenching Oil
Quenching oil increases the wetting of steel during the quenching process, which helps prevent cracks.
Oil quenching works best for knives, blades, and some hand tools because these types of steel are generally rated for oil quenching. Furthermore, it quenches faster than compressed air. While it does not quench as fast as water, it causes fewer cracks than quenching with water.
Quenching oils are less efficient than water during quenching because they often form a sludge as the quenching occurs. Sludge and varnish do not evenly absorb into the steel’s surface, so these byproducts change the rate at which different parts of the steel’s surface cool.
This can lower efficiency by making parts of the surface cool slower and also less evenly, creating a nonuniform heat transfer that can lead to distortion and cracking in some cases.
The ability of the oil to properly quench the steel depends on the surface irregularities of the metal. Moreover, oils of different viscosities, or thickness, will have different boiling and igniting points, so it is important to consider thickness when deciding what type of oil to quench with.
When using quenching oil, it is also important to note water content, as water contamination in quenching oils can lead to increased cooling rate and cause staining or cracking.
Certain types of quenching oils work better for different people depending on the financial situation, environmental intentions, and what you are welding. The most common quenching oils are motor oils, mineral oils, vegetable oils, and commercial oils.
a. Vegetable Oil
If you want to use vegetable oil for quenching, coconut oil is a great option. Not only is it an effective quenching oil, but it will also leave your forge smelling great.
Generally, vegetable oils are a good option for at-home blacksmiths, as they are widely accessible and easy to use.
One issue with coconut oil is its cost- it is generally more expensive than other vegetable oils.
However, vegetable oils are the most home-friendly quenching oil due to their general accessibility and lack of additives.
b. Motor Oil
Motor oil can easily be used for quenching. Even used motor oil can be used for quenching, so this is a great option if you have extra or want to save money.
Motor oil that has been used in a vehicle can be obtained easily or even for free but may contain contaminants from being inside the vehicle.
Furthermore, motor oil can be dangerous or unpleasant, as it releases strong-smelling toxins and additives.
To quench with motor oil, you should work in a well-ventilated space and wear protective gear.
c. Mineral Oil
Mineral Oil works just as well as motor oil but does not have the same toxins or additives, so it is a safer alternative.
It can be bought in bulk from Amazon, such as this Mineral Oil by Pure Organic Ingredients. However, it is more expensive than motor oil, which is often free.
Luckily, even if you do not have access to mineral oil, you can use baby oil. Surprisingly, this oil works as a substitute for mineral oil in quenching metal!
If you are environmentally conscious, keep in mind that these oils are not biodegradable, so they do have a negative impact on the environment and may release toxins at high temperatures.
d. Commercial Quenching Oil
Commercial quenching oils are oils made specifically for the quenching process.
These oils are specifically made for different steels and alloys, so you can ensure they will create high-quality products.
While these oils are a great option for professional blacksmiths, they are usually more expensive than other oils.
Water can also be used to quench metals. It has a low viscosity (because it is very thin), so it evaporates quickly and rapidly exchanges heat with the metal.
These properties allow water to cool metal faster than other quenching mediums.
While water makes metal significantly harder through quenching, it can also make it brittle and susceptible to cracking.
This is one tradeoff of using water instead of oil, as water makes the metal more likely to crack than oil.
To quench a workpiece in water, the workpiece will be submerged in a tank of water until the workpiece and the water are room temperature.
Water is more sustainable than other quenching substances, as it has a low environmental impact.
Since water is highly accessible, it is also generally low-cost.
3. Compressed Air
Compressed air is one of the less commonly used mediums for quenching. When metal is left out to cool in the air, that is technically “air quenching.” However, submerging the metal in air that is compressed allows it to cool faster than it would in normal air.
While this method is effective, it does not drastically alter the structure of the metal or make it significantly harder.
Therefore, for stronger or harder tools, you may want to use an alternate medium. However, it is also less likely to cause cracks or brittle nature in the metal, making it more flexible than other substances.
Generally, compressed air is accessible and low-cost.
In conclusion, blacksmiths use many mediums to quench. The most common quenching substances are water, compressed air, and quenching oil.
Water and compressed air are the most sustainable and affordable quenching methods, but water may cause cracks in the fluid.
Compressed air may also be a less desirable option due to its inability to vastly affect metal’s property.
Blacksmiths also use oils to quench. While commercial quenching oil is the best quality and the most specific oil, motor oil, mineral oil, and even vegetable oil can yield positive results when quenching.