What is TNK heat treatment? Explaining the processing methods, types, benefits, and more!

Heat treatment is carried out to improve hardness, strength, and wear resistance, as well as to remove internal stress, and is used in a wide range of products, mainly automotive and machine parts, and is also available at Sanwa Needle Bearings.

In this article, we will introduce in detail the heat treatment technology that our company offers.We will also provide easy-to-understand explanations of common heat treatments such as quenching, tempering, and normalizing, as well as the heat treatment furnaces used.

What is heat treatment?

Heat treatment is a processing method that changes the material properties of metals by heating them.

Heat treatment is performed on a variety of materials, both ferrous and non-ferrous, but there are many different types of heat treatment for steel in particular, and they are used depending on the application.

【Related article】
What is metal heat treatment? Explanation of the main types such as quenching, tempering, and annealing

Steel Heat Treatment

Steel refers to iron or steel materials with a carbon content of approximately 0.02 to 2 wt%.

As a general rule, the higher the carbon content, the harder the steel will be, but there are complex factors involved, which require the selection of appropriate materials and optimal heat treatment conditions.

The most common types of heat treatment for steel are as follows:

1. Annealing
2. Tempering
3. Quenching
4. Tempering

Annealing

This is a process in which heated steel is slowly cooled (furnace cooling).The main purpose is to soften the steel to improve its workability and to restore the metal structure deformed by plastic processing.

This is also called annealing or hardening.

There are several treatment methods, such as full annealing, spheroidizing annealing, and stress relief annealing, and it is necessary to select the appropriate treatment that suits your purpose.

Tempering

This is a process in which heated steel is cooled at room temperature (air cooling).Like annealing, it restores the metal structure deformed by plastic processing, but compared to annealing, it refines the metal structure and provides a certain degree of strength.

This is also called normalizing.

Quenching

This is a process in which heated steel is rapidly cooled.Quenching transforms the steel into martensite, a structure with extremely high hardness.

The cooling method varies depending on the material, and includes water cooling, oil cooling, and gas cooling.

Tempering

If left as is, hardened steel is too hard and brittle.The hardened steel is then tempered to give it enough toughness to be used as a product.

There are two types of tempering: low-temperature tempering and high-temperature tempering, which are used depending on the material and the intended use of the product. Quenching + high-temperature tempering is sometimes called "thermal refining".

Types of heat treatment furnaces

Heat treatment furnaces can be broadly divided into continuous and batch types.

The continuous type is a method in which the inside of the furnace is heated uniformly with a set temperature distribution, and the product is passed through it on a conveyor or the like to perform heat treatment.Since the inlet and outlet are separate, products can be added continuously and automation can be easily implemented, enabling efficient processing.

However, since it is difficult to make detailed changes to the processing conditions, this method is intended for mass production.

The batch method is a heat treatment method in which the temperature is controlled in a closed space.This method offers a high degree of flexibility since various heat treatment conditions can be set by programming.

However, since it is necessary to create the packaging for one processing run and perform tasks such as loading and unloading, this method is inferior to the continuous method in terms of mass production. This method is suitable for small-lot, high-mix production.

We own both continuous and batch type furnaces and can handle both mass production and small-lot, multi-variety production.

Heat treatment atmosphere

The atmosphere in heat treatment refers to the gas that fills the furnace.

Broadly speaking, there are atmospheric furnaces that heat in air, atmospheric furnaces that heat by filling the air with a special gas, and vacuum furnaces that heat in a vacuum state.

1. Atmospheric furnace
2. Atmosphere Furnace
3. Vacuum Furnace

Atmospheric furnace

No prior preparation or special equipment is required for processing, making this the simplest and least expensive method.

However, at high temperatures, the steel surface reacts with oxygen in the air, forming scale (a layer of oxide) on the surface and causing decarburization (a phenomenon in which the amount of carbon on the surface decreases).

Atmosphere Furnace

It is the most widely used industrial heat treatment furnace.Various gases are used, and depending on the characteristics of the gas, it is possible to perform special treatments such as carburizing (a process that increases the amount of carbon on the surface to make it harder) and nitriding (a process that incorporates nitrogen into the surface to make it harder).

However, atmospheric furnaces require precise control of the amount of gas, and therefore require appropriate equipment.

Vacuum Furnace

The advantage of a vacuum furnace is that it heats while creating a vacuum, completely eliminating the adverse effects of gases on products.This allows us to create products with a beautiful surface finish.

On the other hand, the disadvantage is that complex equipment is required, which results in high processing costs, equipment costs, and maintenance costs.

TNK Heat Treatment

We own the following heat treatment equipment:

We specialize in quenching and tempering martensitic stainless steel, but can also accommodate a wide range of materials and processing conditions.

◾️Solution treatment

◾️Aging treatment

We have several metal heat treatment technicians on staff who can propose optimal conditions based on their knowledge and experience.

We will also consider processing for materials and processing conditions other than those listed above.