Common heat treatment methods and applications of steel

Annealing (stewing)

Description: annealing is to heat steel pieces (or billets) to a suitable temperature, keep them warm for a period of time, and then slowly cool them down (generally furnace cooling).

Application: used to eliminate the internal stress of casting, forging and welding parts, reduce the hardness, so as to facilitate cutting, refine metal grains, improve structure and increase toughness.

Normalize (normalize)

Description: normalizing is to heat the steel to the phase transition point above 30 ~ 50℃, heat preservation for a period of time, and then in the air cooling, cooling rate faster than annealing.

Application: used for heat treatment of low and medium carbon structural steels and carburized parts to refine the microstructure, increase strength and toughness, reduce internal stress and improve cutting performance.


Description: quenching is to heat steel to a certain temperature above the phase transition point, keep it warm for a period of time, and then put it into water, salt water or oil (some materials in the air) to cool down sharply, so that it gets a high hardness.

Application: used to improve the hardness and strength limit of steel. But quenching causes internal stress to make the steel brittle, so it must be tempered after quenching


Note: tempering is the process of heating brittle steel to a temperature below the phase transition point, holding it for a period of time, and then cooling it down in air or oil.

Application: used to eliminate the brittleness and internal stress after quenching, improve the plasticity and impact toughness of steel

Quenched and tempered

Description: high temperature tempering after quenching

Application: used to make steel with high toughness and sufficient strength, many important parts are tempered and heat-treated

Surface hardening

Description: quench the surface of parts only. The surface of the parts has high hardness and wear resistance, while the core keeps the original strength and toughness

Application: commonly used for heat treatment of gear surfaces


Description: heating steel ≤ 120 ~ 130℃, after a long time heat preservation, with the furnace or take out in the air cooling

Application: used to eliminate or reduce the micro stress after quenching, prevent deformation and cracking, stabilize the shape and size of the workpiece and eliminate the residual stress of machining


Description: carburized the surface, carburized layer depth 04 ~ 6mm, hardness of 56 ~ 65HRC

Application: increase wear resistance, surface hardness, tensile strength and fatigue limit.

Suitable for low - carbon, medium - carbon (w c < 0.04%) medium - sized parts and large heavy - duty, impact, wear - resistant parts.

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