How to Heat Treat Steel? Four Heat Treatment Processes for Steel and Goals

Steel is one of the most important engineering materials in modern manufacturing. It is used in a wide range of applications such as construction, automotive, machinery, and aerospace.

However, steel needs to have different properties in different applications, which need to be regulated and optimized by heat treatment processes.

The four basic heat treatment processes for steel include annealing, normalizing, quenching, and tempering, each of which aims to change the internal organization of steel by controlling the heating, holding, and cooling processes to improve its physical, chemical, and mechanical properties to meet the needs of different engineering applications.

In this article, Brother Furnace will delve into the principles and purposes of these four heat treatment processes, and introduce how the bogie hearth furnace plays a key role in these processes.

1. Annealing

What is Annealing?

Annealing is a heat treatment process designed to reduce the hardness of steel and enhance its plasticity and toughness. By heating the steel to an appropriate temperature and cooling it slowly, annealing removes stresses within the steel, reduces brittleness, and improves workability and mechanical properties. Annealing also improves the structure of the steel, making it smoother for subsequent processing.

The Process of Annealing

The annealing process consists of three main stages: heating, holding, and cooling. In the heating stage, the steel is heated to a specific temperature (usually between 700°C and 900°C) to bring its internal organization to a state of recrystallization.

The holding stage ensures that the steel is kept at this temperature for a sufficient period to achieve homogenization of the tissue. Finally, during the cooling phase, the steel is usually cooled at a slow rate to avoid creating new internal stresses.

Why is the Annealing Process Needed?

Reduces hardness: Facilitate cutting and machining and increases productivity.

Eliminate defects: Improve the internal organization of the steel and reduce defects such as cracks and porosity.

Reduce internal stress: Improve the stability and service life of steel.

Brother Furnace's bogie-type annealing furnaces are specially designed for steel annealing, adopting advanced temperature control technology to ensure the uniformity and stability of the heating process.

2. Quenching

What is Quenching?

Quenching is a heat treatment process that increases the hardness of steel through rapid cooling. Its main purpose is to increase the hardness and strength of steel while maintaining high wear resistance. Hardening is commonly used in the manufacture of components that are subjected to high mechanical loads, such as gears and bearings.

The Process of Quenching

The quenching process consists of three stages: heating, holding, and rapid cooling. The steel is first heated to an interval above its critical temperature, usually between 800°C and 1000°C. It is then rapidly immersed in a cooling medium (e.g. water, oil, or a special coolant) to reduce the temperature quickly. The rapid cooling causes changes in the internal structure of the steel, thus increasing its hardness.

Why is the Quenching Process Needed?

Improvement of hardness: Quenched steel is significantly harder and is suitable for application scenarios where high hardness is required.

Formation of martensite: The martensitic organization gives the steel excellent mechanical properties and wear resistance.

Increased Strength: Hardened steel is stronger and able to withstand greater loads.

3. Tempering

What is Tempering?

Tempering is a secondary heat treatment process for hardened steel, the main purpose of which is to reduce the brittleness of the steel while maintaining a certain level of hardness and strength. While quenching can significantly improve hardness, it often makes the steel too brittle, and tempering is used to alleviate this problem by improving the toughness and impact resistance of the steel.

The Tempering Process

The tempering process usually consists of three steps: heating, holding, and cooling. During the tempering process, the steel is heated to a lower temperature (usually between 150°C and 700°C) and then held for a certain period to allow the internal stresses in the steel to be released. Afterward, the steel is slowly cooled to room temperature. This process adjusts the microstructure of the steel to balance hardness and toughness.

Why is the Tempering Process Necessary?

Elimination of internal stresses: Tempering significantly reduces the internal stresses generated during the hardening process and improves the stability of the steel.

Improve toughness: Tempered steel has increased toughness and is less prone to brittle fracture.

Adjustment of mechanical properties: By adjusting the tempering temperature and holding time, we can obtain steel products with different mechanical properties.

Brother Furnace's bogie hearth furnaces are equipped with a precise heating control system, which can provide a uniform heating and cooling environment for steel. By tempering the steel in the bogie hearth furnace, the properties of the steel can be effectively adjusted to ensure that it has a good overall performance in practical applications.

4. Normalizing

What is Normalizing?

Normalizing is a heat treatment process designed to improve the organization and properties of steel. Its main purpose is to refine the grain size of steel and improve its uniformity and mechanical properties. Normalizing can eliminate the casting and forging process of uneven organization so that the mechanical properties of are steel more stable.

The Process of Normalizing

The normalizing process consists of three steps: heating, holding, and air cooling. The steel is heated above its critical temperature (generally between 850°C and 950°C) and then held at that temperature for a certain period to complete recrystallization of the tissue. Next, the steel is cooled in air to homogenize its organization. This treatment helps to improve the mechanical properties and machinability of the steel.

Why is the Normalizing Process Needed?

Increase hardness and strength: To enhance the load-carrying capacity and wear resistance of steel.

Refinement of grain: Improve the organization of steel and its comprehensive performance.

Eliminate internal stress: Similar to annealing, normalizing can effectively eliminate the internal stress of steel and improve its stability.

Bogie Hearth Furnace: Professional Steel Heat Treatment Equipment

Heat treatment processes for steel include annealing, quenching, tempering, and normalizing, each with its own unique purpose and application scenario. The successful implementation of these processes relies on stable and precise heat treatment equipment.

As a specialized manufacturer of bogie hearth furnaces, Brother Furnace is committed to providing state-of-the-art bogie hearth furnaces to meet the needs of steel in different heat treatment processes.

Brother Furnace's bogie hearth furnaces not only provide superior temperature control and heating performance but also ensure the efficiency and stability of the treatment process.

If you are looking for a machine that can provide excellent heat treatment results, Brother Furnace is undoubtedly your best choice. By choosing a cart furnace, you will be able to achieve precise control over the properties of your steel, resulting in increased productivity and product quality.

Contact us for more information and let us help you succeed in the field of steel heat treatment.