What is Quenching?
Quenching is a technique for quickly cooling an evenly heated metal to minimize and regulate the impact of slow cooling on the structure and, therefore, the metallurgical characteristics of the metal. There are different types of quenching media, but this article will examine oil as a form of quenching media in the heat-treatment process. (We will not discuss the gas forge)
What exactly is quenching oil?
Oil is a typical medium for quenching a blacksmithing workpiece. Many types of quenching oils are available for this purpose, but some are superior to others in specific situations. While the characteristics of these oils vary considerably, it is also reasonable to examine their price, accessibility, and suitability with the grade and kind of steel being quenched.
How Do Oils Act as a Coolant for Metals?
The quenching procedure is divided into many stages. Firstly, when a hot workpiece contacts the quenching oil for the first time, a vapor layer develops around the metal as it is fully immersed. Different circumstances stabilize this vapor layer.
The metal's and quenching oil's characteristics may significantly impact the reliability of the vapor blanket around the workpiece. Nucleate boiling occurs when the vapor blanket is disturbed. This stage of the process exhibits the highest heat transfer rates. The chemical composition of the particular quenching oil has a significant effect on when and how quickly this process occurs.
Convective cooling begins when the process temperature falls below the boiling point of the oil. This step's cooling pace is highly reliant on the stickiness of the quench oil, which is itself highly dependent on its purity.
Is There an Optimal Quenching Oil?
The kind of oil you choose is very dependent on the materials and project. While there is no one-size-fits-all quenching oil, some types or grades of steel may be more fitted for quenching than others in a given application. This is a critical aspect to consider after you have a firm grasp on the properties of the metal you want to quench. And because the circumstances of quenching are not uniform, the oils used for quenching should be selected based on their characteristics.
Steels and alloys are quenched at varying initial temperatures and cooling speeds to ensure the final product's homogeneity and quality. Mineral oils and oil-hardened steels are two of the most frequent metal and oil pairings because mineral oil serves as a medium quenchant.
Factors To Consider When Purchasing Quenching Oils
Costs of Quenching Oil
Cost is a primary consideration when blacksmiths choose a quenching oil. This is a critical and relevant consideration since it may be influenced by the efficacy of a specific oil in a given application or simply by the oil's availability.
If you are a beginning blacksmith who wants to begin working on projects that need the quenching process in oil, it may be wise to start with less expensive oils to practice and improve your skill.
Rate and Speed of Oil Quench
The oil's viscosity (resistance to deformation) affects the pace of quench, with lower viscosity lubricants enabling more heat transfer.
Other physical characteristics of quenching oil may also significantly affect its efficiency in quenching a specific steel type. Special quenching rates are required for certain metals to avoid structural cracks or distortions.
Oils' environmental impact
Although many oils used in food are edible, motor oils and electronically controlled fluids are not. Environmental impact is a critical factor to consider when selecting a quenching oil. This factor affects how you dispose of the oil and the number of times you can recycle a quenching oil and make the most of your resources.
Types of Quenching Oils for Blacksmiths
When it comes to blacksmithing and bladesmithing, motor oils are a popular kind of quenching oil. Both new and old motor oils are suitable for quenching purposes and are readily accessible. Typically, fresh motor oil is less expensive to use than industrial quenching oils.
Oils Suitable for Human Consumption
There are many quenching oils suitable for blacksmithing that are food-grade. Vegetable, peanut, and avocado oils are just a few of the available choices. Canola, olive, and palm kernel oils are all examples of vegetable oils. Vegetable oil is very affordable and is derived from renewable resources. They are sustainable and may even be recovered for use as biofuel. When used as a quenching oil, vegetable oils have higher impact energy values.
Mineral Oils & Transmission Fluids
Mineral oils and automatic transmission fluids may be used in place of motor oils. Indeed, these oils do not include the additives for which motor quenching oils are notorious in blacksmithing. If you cannot get mineral oils, baby oil is an excellent substitute, including additional fragrance. Mineral oil quenchants are ideal for steels that need a rapid quench rate, as well as for oil-hardened steels.
The purpose of using oil for quenching is to provide a slower cooling rate than water, which helps prevent cracking caused by unequal stresses in hard materials. If you quench in water, you risk breaking a steel component that needs a slower cooling rate. When an air-hardening steel component is quenched in oil, it is prone to fracture. If you immerse water-hardening steel in oil, it is likely to become overly soft. Determining the appropriate quench oil requires knowledge about the type of steel. This is why high-quality steel is the ideal material to use when manufacturing knives.