Starting in the knifemaking industry may be a challenging experience for some individuals. For a novice, learning about anvil work, all these various kinds of metal, forging methods, equipment, and the heat-treating process may be daunting.
We will cover all you need to know about the tempering process of a knife in this post.
What exactly is tempering?
Heat treatment at low temperatures is called tempering. It is used to modify materials' hardness/toughness ratio after other heat treatment methods have been exhausted.
The maximal hardness of a steel grade, achieved via hardening, results in a low toughness for the material. Tempering decreases the material's hardness and improves its toughness. Tempering allows you to tailor the characteristics of a material (hardness/toughness ratio) to a specific application.
Tempering Materials & Application
Tempering may be classified into three broad categories:
Low temperature (160-300°C): used to case hardening materials and work tool steels at low temperatures. Typically, the required hardness is about 60 HRC.
Tempering of spring steels (300-500°C): utilized in the manufacture of spring steels and related materials. Typically, the required hardness is about 45 HRC.
High temperature (500°C or greater): utilized for quenched and tempered steels, high-temperature tool steels, and high-speed steels. The hardness of the material varies between 300HB and 65HRC.
What are tempering processes?
Tempering temperatures may range from 160°C to 500°C or more, depending on the needs and steel quality. Tempering is often carried out in furnaces that have a protective gas option. Protective gas shields the surface against oxidation throughout the process and is often utilized at elevated temperatures.
Holding time at the tempering temperature is critical for some kinds of steels; a prolonged holding time corresponds to a higher temperature. In specific temperature intervals, depending on the steel quality, a condition called temper brittleness may develop. Generally, tempering inside this temperature range should be avoided. These regions and the optimal temperature for meeting hardness criteria are detailed in steel manufacturers' steel catalogs.
How Often Should a Knife Be Tempered?
The material's intended use primarily determines the quantity of tempering required. Therefore, if you want to create a beautiful, high-quality knife, it must be sufficiently robust for optimum benefit. Bear in mind that the greater the temperature utilized to temper the blade, the softer it will be. On the other hand, the lower it is, the tougher but more brittle the material becomes.
For example, a kitchen knife is often tempered at lower temperatures due to its intended usage. On the other hand, since hunting knives are used for severe cutting, they are tempered at a greater temperature. Thus, to ensure a decent blade in the end, a temperature exceeding 600°F may significantly weaken the blade. Additionally, avoid going too low since you risk not reducing the hardness enough.
Low temperature is suggested if the material is used for anything different from its original purpose when great hardness is unnecessary.
In most instances, two 2-hour tempering sessions at approximately 400°F should be enough. And to ensure optimum performance, the blade should be allowed to cool completely between cycles. After the second tempering process, the blade is typically thoroughly tempered and ready to be finished into a knife. Keep in mind that the heat must be maintained. The knife becomes tough after the tempering process, indicating nearly ready for usage.
Is It Necessary to Temper a Knife?
The purpose of hardening is, as the name implies, to harden the blade of the knife. A knife is hardened by heating it to between 1800 and 2000 degrees Fahrenheit and rapidly quenching it in oil or water.
Your blade has become very hard due to the quenching process, which is a positive development. The downside is that it is also very fragile. That is where the tempering procedure comes into play to alleviate the brittleness issue. Tempering's main objective is to decrease the knife's hardness in return for increased ductility. For example, what is the purpose of having a razor-sharp, hard knife if it is so fragile that it would shatter into a million pieces if dropped accidentally?
In a nutshell, yes, you must temper a knife. Tempering reduces the hardness of your knife somewhat but increases its toughness and durability. Without tempering, your blade is far more prone to fracture, rendering it ineffective. There are very few instances in which tempering a knife is not necessary.
Tempering vs. Hardening: What's the Difference?
It is not unusual for a novice to get perplexed by the many heat treatment components and other knife manufacturing terminologies. I've observed that many folks continue to confuse the tempering and hardening processes, so let's clear things up.
In a nutshell, hardening is the process of heating steel to a non-magnetic temperature and quickly quenching it in oil or water. As the name implies, the objective is to enhance the steel's hardness. On the other hand, tempering is heating the steel below its critical temperature, often in an oven. Its main objective is to improve strength and durability by decreasing the hardness.
It has been observed that tempering may result in the loss of tensile stress. If you're going to utilize the metal to create a knife, it's critical to heat it gradually to prevent breaking it. After that, the metal should be kept at a set temperature for a specific time. Each inch should take an hour, followed by cooling the metal in calm air and forging it into a knife.