Heat treatment methods for iron screws

Heat treatment methods: Different heat treatment methods can be selected according to different objects and purposes.

Quenched and tempered steel: high temperature tempering after quenching (500-650℃)

Spring steel: medium temperature tempering after quenching (420-520℃)

Carburizing steel: quenching after carburizing and then low temperature tempering (150-250℃)

After low-carbon and medium-carbon (alloy) steels are quenched into martensite, as the tempering temperature increases, the general rule is that the strength decreases, while the plasticity and toughness increase. However, due to the different carbon content in low-carbon and medium-carbon steels, the tempering temperature has different effects on them. Therefore, in order to obtain good comprehensive mechanical properties, the following approaches can be taken respectively:

(1) Select low-carbon (alloy) steel, and temper it at a low temperature below 250℃ after quenching to obtain low-carbon martensite. In order to improve the surface wear resistance of this type of steel, only the carbon content of each surface layer can be increased, that is, surface carburizing is performed, which is generally called carburized structural steel.

(2) Take medium carbon steel with high carbon content, and perform high temperature (500-650℃) tempering (so-called quenching and tempering treatment) after quenching, so that it can maintain sufficient strength under high plasticity. This type of steel is generally called quenched and tempered steel. If you want to obtain high strength, but would rather reduce plasticity and toughness, you can use low temperature tempering for the steel with low carbon content, and you will get the so-called "ultra-high strength steel".

(3) Steels with carbon content between medium carbon and high carbon (such as 60, 70 steel) and some high carbon steels (such as 80, 90 steel), if used to make springs, in order to ensure high elastic limit, yield limit and fatigue limit, medium temperature tempering is used after quenching.