Screw heat treatment, also known as screw hardening. Screws can be divided into iron and Stainless steel screws, as well as other materials such as aluminum and copper. Iron generally needs to be harder and requires hardening. But Stainless steel screws rarely need to be hardened because they are relatively hard, and stainless steel cannot be hardened through heat treatment. Please take a look at the heat treatment method for iron screws below.
1、 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: quenched and tempered at medium temperature (420-520 ℃)
Carburized steel: quenched after carburization and then tempered at low temperature (150-250 ℃)
Low and medium carbon (alloy) steels quenched into Martensite, with the increase of tempering temperature, the general rule is that the strength decreases, and the plasticity and toughness increase. However, due to the different carbon content in low and medium carbon steels, the impact of tempering temperature on them varies. So in order to achieve good comprehensive mechanical performance, the following methods can be adopted:
(1) Low carbon (alloy) steel is selected and tempered below 250 ℃ after quenching to obtain low carbon Martensite. In order to improve the surface wear resistance of this type of steel, only by increasing the carbon content of each surface layer can surface carburization be carried out, commonly known as carburized structural steel.
(2) Adopting medium carbon steel with high carbon content, quenching and tempering at high temperature (500-650 ℃) (also known as quenching and tempering treatment) to maintain sufficient strength under high plasticity conditions, this type of steel is generally referred to as quenched and tempered steel. If one wishes to obtain high strength and prefers to reduce plasticity and toughness, low-temperature tempering can be adopted for low carbon content gold containing quenched and tempered steel, thus obtaining the so-called "ultra high strength steel".
(3) For steel grades with carbon content between medium and high carbon (such as 60 and 70 steels) and some high carbon steels (such as 80 and 90 steels), if they are used to manufacture springs, in order to ensure high Elastic Limit, yield limit and Fatigue limit, they shall be tempered at medium temperature after quenching.
2、 Operation process
(1) Quenched and tempered steel
1. Preheating treatment: normalizing → annealing (pearlitic steel) → high temperature tempering (martensitic steel)
The purpose of normalizing is to refine the grains, reduce the degree of banding in the organization, and adjust the hardness to facilitate mechanical processing. After normalizing, there are equiaxed fine grains just now.
2. Quenching: Heat the cylinder body to around 850 ℃ for quenching, and the quenching medium can be selected based on the size of the steel piece and the hardenability of the steel. Generally, water, oil, or even air quenching can be chosen. Steel in a quenched state has low plasticity and high internal stress
3. Tempering:
=1  * GB3 ① In order to make the steel have high plasticity, toughness, and appropriate strength, the steel is subjected to high-temperature tempering at around 400-500 ℃. Steel with high sensitivity to temper brittleness must be rapidly cooled after tempering to suppress the occurrence of temper brittleness.
=2  * GB3 ② If the parts are required to have particularly high strength, they shall be tempered at about 200 ℃ to obtain medium carbon tempered Martensite structure.
(2) Spring steel:
1. Quenching: Oil quenching at 830-870 ℃.
2. Tempering: Tempering at around 420-520 ℃ to obtain tempered troostite structure.
(3) Carburized steel:
1. Carburization: A type of chemical heat treatment that refers to the penetration of C element into the surface of steel parts in an active medium containing a certain chemical element at a certain temperature. Pre heating (850 ℃) carburization (890 ℃) diffusion (840 ℃) process
2. Quenching: Carbon and low alloy carburized steel, generally using direct quenching or one-time quenching.
3. Tempering: Low temperature tempering to eliminate internal stress and improve the strength and toughness of the carburized layer.