Best Types Quenching Oil for Blacksmithing 2020 [Updated]


Working the Flame is supported by it’s readers. We may earn commission at no extra cost to you if you buy through a link on this page. As an Amazon Associate we earn from qualifying purchases.

Different Types of Quenching Oils for Blacksmithing 2020 (Compared)

There are many different types of quenching oils available, all with various pros and cons. Photo by Matthew Pallady CC BY-SA

The quenching process is a very important step in the blacksmithing process when working with heated metals. Quenching is a form of rapidly cooling a uniformly heated metal to limit and control the effect that slow cooling has on a metal’s microstructure and, therefore, its metallurgical properties.

One of the common media in which a blacksmithed workpiece can be quenched is oil. There are many kinds of quenching oils available to perform this task, but some may be better than others for certain applications.

The common quenching oils that we will discuss are motor oils, food-grade oils, mineral oils and automatic transmission fluids, and commercial quenching oils. Although the properties of these oils can vary greatly, it is also important to consider their cost, availability, and compatibility with the grade and type steel you intend to quench.

Park's AAA Quench Oil - 1 Gallon Jug
  • Appearance: Light Amber Oil, Viscosity @ 100°F: 14.0 – 19.3 cSt
  • Nickel Ball Time: 9 – 11 seconds, Flash Point: > 340°F
  • Parks AAA is considered a medium to medium fast oil. Many times a quench oil is described in seconds...

How Do Oils Work to Quench Metals?

The quenching process is made up of different steps. When a heated workpiece first comes into contact with the quenching oil, a vapor layer forms around the metal as it is completely submerged. This vapor layer is stabilized by different conditions.

The properties of the metal and those of the quenching oil can greatly affect the stability of the vapor blanket surrounding the workpiece. Once the vapor blanket is destabilized, nucleate boiling takes place.  This step in the process features the most rapid rate of heat transfer. The molecular composition of the individual quenching oil plays a large role in determining when this step takes place and how fast it is.

Once the process temperature decreases below the oil’s boiling point, the process transitions to the convective cooling step. The cooling rate in this step is heavily dependent on the viscosity of the quench oil, which, in turn, is dependent on its purity. Below is a great video showcasing the quenching process in two different media, both oil and water:

As previously mentioned, the properties of quenching oils can vary greatly based on the type of oil being used. This variation affects the way in which the oil quenches a metal. Some of the effects it can cause are manifested as structural changes to the work metal that are more favorable at lower temperatures, like phase transformations.

Phase transformations could increase the density of a metal’s crystal lattice, causing it to harden. The hardness of a metal can determine how pliable or brittle it is, making this an important characteristic to be able to control.

Is There Actually a Best Quenching Oil?

The type of oil you choose largely depends on your choice of materials and project. Photo by Ben Osteen CC BY-SA

While there may not be an overall best quenching oil type, there are quenching oils that may be better-suited for quenching certain types or grades of steels in a particular application than others. This factor is very important to consider once you understand the characteristics of the metal you intend to quench.

Since the conditions of the quenching process are not universal to all metal types, it makes sense that the oils used for quenching are chosen based on the properties unique to the particular steel or steel alloy being quenched.

Steels and alloys undergo quenching at different starting temperatures and cooling rates to promote the uniformity and quality of the finished product. One of the common metal and oil combinations are mineral oils and oil-hardened steels, because it acts as an intermediate-rate quenchant.


Considerations When Buying Quenching Oils

1) Oil Quenching Costs

Many food grade oils are both biodegradable and much cheaper than commercial quench oils.

The factor at the forefront of many blacksmiths’ minds when choosing a quenching oil, is its cost. This is a very important and valid factor to consider, because cost can be affected by the effectiveness of a particular oil in an application or simply by the availability of the oil.

If you are a beginner blacksmith who would just like to get started with some projects involving the quenching process in oil, it may be more prudent for you to start using cheaper oils to practice and refine your technique.

If you are an advanced blacksmith trying to find the perfect quenching oil for your application, regardless of the cost, it would make more sense to pick the ideal oil type for your project – often in the form of commercial quench oils.


 2) Oil Quench Rate and Speed

Viscosity (resistance to deformation) affects quench rate, with lower viscosity oils providing higher heat transfer.

The other physical properties of quenching oil can also have a significant effect on how efficient it is at quenching a particular steel type. Some metals require certain quenching speeds to prevent any cracking or distortion in its structure.

As briefly discussed, the viscosity of oil can accelerate or decelerate convective heat transfer step in the quenching process, also referred to as the quench rate. The lower the viscosity of a particular oil, the faster the rate of heat transfer is. It is also important to note that the viscosity can also be affected by the degradation of the oil that takes place as it is used in the quenching process. This degradation is characterized by the presence of oxidation by-products in the oil, which can also cause an increase to the overall fluid’s viscosity and lower the rate of heat transfer.

Another physical property that can affect the quench rate is the water content of the oil. This property also affects the look and quality of the finished workpiece if it does not cause a fire in combination with the oil. Since water has very different properties from oil, more than two percent of the water content in a quenching oil could create irregularities on the surface of the workpiece and a dangerous combination. This is a form of contamination that can greatly alter the rate of heat transfer on different parts of the metal’s surface due to thermal gradients.


3) Environmental Impact of Oils

Many food grade oils are biodegradable, but motor oils and automatic transmission fluids are not.

The environmental impact that a quenching oil has is a very important factor to consider when choosing a quenching oil. This factor not only impacts the way in which you dispose of the oil, but the amount of times that you can re-use a quenching oil and get the most out of your supplies.

For example, premium quenching oils can last years before needing to dispose of them. In large-scale settings, oil filtration and circulation systems are currently used to optimize the use of quench oil due to the increasing costs of oil and its proper disposal. The recyclability of quench oils can decrease your carbon footprint. Some oils can even be reclaimed as bio-fuels, further optimizing their use.


Different Types of Blacksmith Quenching Oils (Comparison)

1) Motor Oils

Valvoline - 881164-EA Advanced Full Synthetic SAE 5W-30 Motor Oil 5 QT
  • For best performance, follow the manufacturer's recommendations in your vehicle owner’s manual.
  • Excellent engine cleanliness through superior sludge and varnish protection
  • Outstanding high-temperature protection under severe driving conditions and superior...

Motor oils are a common type of quenching oil used in both blacksmithing and bladesmithing applications. New and used motor oils can be used for quenching and are both widely available. New motor oil is typically cheaper to use than commercial quenching oils.

Used motor oil is oftentimes free or easy to obtain, but it can contain a few contaminants from being used in a vehicle. Unfortunately, both new and used motor oil have additives that can release toxins when the hot metal workpiece comes into contact with the oil during the quenching process. These toxins typically give off an undesirable smell during quenching. It is always wise to avoid inhaling these toxins and to wear the proper safety gear for your application.

Quenching with motor oil should be done in a space with enough ventilation. Due to the contaminants found in motor oils, a lot of blacksmiths who use it, find that there is a thin dark film on their finished workpiece after quenching.

Advantages  Disadvantages 
  • Can be cheap whether it is new or used
  • Widely accessible
  • Commonly used in bladesmithing
  • Used motor oil can have a lot of contaminants
  • Motor oils have additives that release toxins during the quenching process
  • Toxins smell bad during quenching
  • Should only be used in a well-ventilated space
  • Smell from quenching motor oil should never be inhaled
  • Can cause staining on workpiece from contaminants

 

2) Food-Grade Oils

Botticelli Chef Select Cooking Oil - Organic Canola Oil for Cooking, Baking & Frying Blended With Organic...
  • WORKS GREAT FOR ALL TYPES OF COOKING - It's called Chef Select as it brings true versatility while...
  • HIGH HEAT TOLERANCE - Botticelli's Chef Select blended cooking oil has high smoke point which makes...
  • CLEAN AND MILD FLAVOR - Each can contains 80% of canola oil organic and 20% organic olive oil extra...

There are many food-grade quenching oil options available to use for blacksmithing. Among these options are vegetable, peanut, and avocado oil. Some commonly used vegetable oils are canola, olive, and palm kernel oil. Vegetable oil is very cheap and comes from renewable sources. They are biodegradable and can even be reclaimed as bio fuels. Vegetable oils have better impact energy values when used as a quenching oil. This characteristic allows them to increase the toughness of the workpiece.

The trade-off with these oil types is the decreased hardness. Peanut oil and olive oil could also be used for similar applications, but they are typically more expensive than common neutral oils.

Advantages  Disadvantages 
  • Cheap to purchase
  • Widely available
  • Renewable sources
  • Recyclable
  • Promotes toughness of workpiece
  • Workpiece does not achieve hardness values as high as when quenched other oil types
  • Some vegetable oils are more expensive than others

3) Mineral Oils & Automatic Transmission Fluids

Mineral Oil (1 Gallon Bucket) by Pure Ingredients, Resealable Bucket, Food & USP Grade, Fragrance-Free,...
5 Reviews
Mineral Oil (1 Gallon Bucket) by Pure Ingredients, Resealable Bucket, Food & USP Grade, Fragrance-Free,...
  • PURE INGREDIENTS Mineral Oil Conditions Wood & Polishes Stainless Steel.
  • BEST VALUE: 1 GAL BUCKET 7 LBS More Than Other Top Sellers. (Seriously, check out their labels.)
  • 100% PURE, FOOD GRADE, PHARMA GRADE.

Mineral oils and automatic transmission fluids are a suitable alternative for motor oils. These types of oils actually do not contain the additives that motor quenching  oils are infamously known for in blacksmithing. If you do not have access to mineral oils, baby oil is another great alternative for them, it simply contains an added scent.

Mineral oil quenchants work great with steels that require a fast quench rate and oil-hardened steels. Mineral oils generally have greater cooling capacities for steel alloys. Their efficiency in the quenching process increases their overall cost.

The environmental impact of mineral oils is not very good, as they are not biodegradable. If these oils are heated to very high temperatures, there is a possibility that dangerous aromatics will start to build up and release toxins into the air.

Advantages  Disadvantages 
  • Alternative for motor oil
  • Baby oil is an alternative for mineral oil
  • Does not contain additives
  • Not biodegradable quenching oil
  • Relatively expensive oil
  • When mineral oils reach high temperatures, they can create toxic aromatics

4) Commercial Quenching Oils

Park's AAA Quench Oil - 1 Gallon Jug
  • Appearance: Light Amber Oil, Viscosity @ 100°F: 14.0 – 19.3 cSt
  • Nickel Ball Time: 9 – 11 seconds, Flash Point: > 340°F
  • Parks AAA is considered a medium to medium fast oil. Many times a quench oil is described in seconds...

Commercial quenching oils are specifically made to be used in the quenching process, as their name suggests. There are a wide variety of commercial quenching oils available to accommodate the different types of steels and steel alloys to be quenched. They are composed in such a way that different commercial quenching oils feature properties that can cause slow or fast quenching rates.

Since commercial quenching oils are made for the purpose of quenching, they are typically the most expensive quenching oil type available. They are not easily accessible at general stores and have higher costs than common oils.

Advantages  Disadvantages 
  • Specifically designed to be used in quenching applications
  • Accommodates different quench rates for different steel and steel alloy types
  • More expensive than non-commercial quenching oils
  • Not widely available

Leave a Comment