What is Tempering?

Tempering is a heat treatment process that alters the mechanical properties (typically ductility and hardness) and relieves the internal stresses of a steel. Tempering allows carbon trapped in a martensitic microstructure to disperse and enables the internal stresses to be released from the steel that may have been created from prior operations.

By carefully controlling the temperature and duration of the treatment, manufacturers can fine-tune the properties of the metal to meet specific performance requirements. The metal tempering process is widely used in industries such as automotive, construction, and aerospace, where durability and resistance to wear are critical.

What is Tempering Metal?

Tempering is a heat treatment process used to improve the toughness and durability of metal. It involves heating a hardened metal, such as steel, to a specific temperature below its critical point and then allowing it to cool in a controlled manner. This process reduces brittleness while maintaining strength, making the metal more resistant to fractures and wear.

What is tempered metal? Tempered metal has undergone this heat treatment to achieve a balance between hardness and flexibility. It is commonly used in tools, automotive parts, and structural components where both strength and resilience are necessary.

Hardening and tempering metal are often performed together to first increase hardness through quenching, followed by tempering to adjust the material’s properties for practical applications. The metal tempering process ensures metals perform well under stress while maintaining durability.

The Metal Tempering Process

Tempering is performed by elevating the steel to a set point below its lower critical temperature, typically following a hardening operation. Once this temperature is reached, it is held there for a specified amount of time. The exact temperature and time depend on several factors, such as the type of steel and desired mechanical properties.

To get the steel to its critical temperature, some type of heating device must be used. Common devices include gas furnaces, electrical resistance furnaces, or induction furnaces. Often, this heating is done in a vacuum or with an inert gas to protect the steel from oxidation. Once the furnace achieves the desired temperature, a dwell time occurs. Following the dwell time, the furnace is shut off, and the steel is allowed to cool at a predetermined rate.

Why is Steel Tempered?

Tempering steel after a hardening process allows for a middle ground of hardness and strength. Without proper metal tempering, steel may either be too brittle to handle stress or too soft to provide the necessary durability. This is achieved by allowing the carbon diffusion to occur within a steel microstructure. When steel is hardened, it can become excessively brittle and hard. However, when not hardened, the steel may not have the strength or abrasion resistance needed for its intended application. By incorporating both hardening and tempering metal, manufacturers can optimize material properties to meet the specific demands of industries such as construction, automotive, and tooling.

Tempering also improves the machinability and formability of a hardened steel and can reduce the risk of the steel cracking or failing due to internal stresses. By relieving the brittleness caused by the initial hardening process, tempering makes the metal easier to cut, shape, and drill.

When is Metal Tempering Used?

Tempering is most commonly used following a quenching operation. Heating a carbon steel and rapidly quenching it can leave it too hard and brittle. Tempering it can restore some of its ductility. By carefully selecting the tempering temperature, manufacturers can adjust the balance between hardness and toughness to meet the specific needs of a component.

Tempering can reduce the hardness and relieve the stress of a welded component. Welds can create a localized zone that has been hardened due to the heat of the welding process. This can leave undesirable mechanical properties and residual stress that can promote hydrogen cracking. Tempering helps prevent this. By applying heat treatment after welding, manufacturers can refine the microstructure, enhance toughness, and minimize the risk of failure.

Work hardened materials often require tempering. Materials can become work hardened through processes such as punching, bending, forming, drilling, or rolling. Work hardened materials have a high amount of residual stresses that can be alleviated through a tempering process. By applying tempering techniques, manufacturers ensure that metals retain sufficient strength while regaining flexibility, reducing the likelihood of fractures or premature wear.