Tempering of Steel

Tempering of steel is a final heat treatment that is always applied after hardening. It consists of heating the hardened steel to a temperature below the critical point AC₁, holding, and cooling, generally in air.

Heating temperatures vary greatly depending on the type of steel.

There are 4 basic types of heat treatment for steel: annealing, normalizing, hardening, and tempering.

Why is tempering necessary after the hardening treatment?

After hardening, steel has an unstable, hard, and brittle structure. Mechanical strength and hardness characteristics are high, but plasticity and toughness characteristics are low

Tempering treatment is applied to steels that undergo physical transformations. Following this treatment, the unstable and brittle state is changed into a more stable and less brittle state.

Tempering of steel – purpose of application:

– eliminating or reducing internal stresses that appear in steel parts after hardening ;

– transforming the martensitic structure of hardened parts into a more stable structure ;

– reducing brittleness ;

– increasing toughness .

The tempering temperature is chosen based on the mechanical characteristics required for the part.

The hardness of the hardened part decreases as this temperature increases, while toughness increases.

The heating time depends on the size of the part and aims to avoid creating internal stresses in the material.

Depending on the temperature, three types of tempering can be distinguished (see the table below).

Low tempering aims to reduce residual stresses in hardened parts, without decreasing their hardness.

High yield strength of the material of the treated parts, in order to ensure good elasticity, is obtained through medium tempering.

And following the high tempering treatment, a part with high mechanical strength and good toughness is obtained.

The tempering temperature influences the mechanical properties by determining the degree of dispersion of carbides in the ferrite-carbide mixture.

Hardening and low tempering can be grouped into a single operation called hardening with self-tempering.

High tempering is the most frequently encountered of the three types detailed above.

Cooling during tempering is done in air, except for alloy steels susceptible to temper brittleness, which are rapidly cooled in water from temperatures of 550-650˚C.

H Metal sells a wide range of metallurgical products subjected to heat treatments.

To receive a concrete offer, please contact us at the email address office@h-metal.ro.