Heat Treatment of Steel Strip Coils: Tempering

Tempering is the quenched metal material or parts heated to a certain temperature, after a certain period of time, in a certain way cooling of the heat treatment process, tempering is an operation immediately after quenching, usually also the workpiece for heat treatment of the last process, so the joint process of quenching and tempering is called final heat treatment. The main objectives of quenching and tempering are:

1) Reduce internal stress and reduce brittleness, quenched parts have great stress and brittleness, such as not tempered in time will often produce deformation or even cracking.

2) Adjust the mechanical properties of the workpiece, after the workpiece is quenched, the hardness is high, the brittleness is large, in order to meet the different performance requirements of various workpieces, it can be adjusted by tempering, hardness, strength, plasticity and toughness.

3) Stabilize the workpiece size. By tempering, the metallographic structure can be stabilized to ensure that no deformation occurs during subsequent use.

4) Improve the cutting performance of some alloy steels.

The tissue obtained by high-temperature tempering is tempered cordite. Tempering is generally not used alone, tempering after the quenching treatment of parts, the main purpose is to eliminate the quenching stress, get the required organization, tempering according to the tempering temperature is divided into low temperature, medium temperature and high temperature tempering. Tempered martensite, tortenite and sorstenite were obtained, respectively. Among them, the heat treatment combined with high temperature tempering after quenching is called quenching and tempering treatment, the purpose of which is to obtain comprehensive mechanical properties with good strength, hardness, plasticity and toughness.

In production, it is often based on the requirements for the performance of the workpiece. According to the different heating temperature, tempering is divided into low-temperature tempering, medium-temperature tempering, and high-temperature tempering. The heat treatment process combining quenching and subsequent high-temperature tempering is called tempering, that is, it has high strength and good plastic toughness. It is mainly used to deal with machine structure parts with large loads, such as machine tool spindles, automobile rear axle half shafts, powerful gears, etc.

Tempering requirements: Workpieces with different uses should be tempered at different temperatures to meet the requirements in use.

1) Tools, bearings, carburized quenched parts, and surface quenched parts are usually tempered at low temperature below 250 °C. After low-temperature tempering, the hardness does not change much, the internal stress decreases, and the toughness is slightly improved.

2) The spring is tempered at medium temperature at 350~500 °C, which can obtain high elasticity and necessary toughness.

3) Parts made of medium carbon structural steel are usually tempered at high temperature at 500~600 °C to obtain a good fit of appropriate strength and toughness.