Screw heat treatment, we also call the screw hard. Screws are divided into iron and stainless steel screws. Iron generally needs to be harder and harder. However, stainless steel screws rarely need to be hardened because of the hardness of the steel itself, which is hard enough. Please see the iron heat treatment method below.
First, the heat treatment method
Different heat treatment methods can be selected depending on the purpose.
Quenched and tempered steel: high temperature tempering after quenching (500-650 ° C);
Spring steel: medium temperature temper after quenching (420-520 ° C);
Carburized steel: after carburizing and quenching, low temperature tempering (150-250 ° C);
After quenching into martensite of low carbon and carbon (alloy) steel, the general rule is that the strength decreases with the increase of tempering temperature. However, due to the different carbon content in carbon steel, the tempering temperature has different effects. Therefore, in order to obtain good comprehensive mechanical properties, the following methods can be used alone: ​​(1) Low-carbon (alloy) steel is selected, and after quenching, tempering at a low temperature of 250 ° C or lower is performed to obtain low-carbon martensite. In order to improve the surface wear resistance of such steels, only the carbon content of each surface layer is increased, that is, surface carburization is performed, which is generally called carburized structural steel. (2) Adopt medium carbon steel with high carbon content, and temper at high temperature (500-650 °C) after quenching (so-called quenching and tempering treatment), so that it can maintain sufficient strength under high plasticity, generally called this The steel is a quenched and tempered steel. If you want to obtain high strength, but prefer to reduce plasticity and toughness, low-temperature tempering can be achieved for gold-containing tempering with lower carbon content, so that the so-called "ultra-high-strength steel" is obtained. (3) Steel grades with carbon content between medium carbon and high carbon (such as 60, 70 steel) and some high carbon steel (such as 80, 90 steel), if used to manufacture springs, in order to ensure high elastic limit , yield limit and fatigue limit, then use medium temperature temper after quenching.
Second, the operation process
(1) Quenched and tempered steel
1. Pre-heat treatment: normalizing→annealing (pearlite steel)→high temperature tempering (martensitic steel). The purpose of normalizing is to refine the grains, reduce the degree of banding in the structure, and adjust the hardness to facilitate mechanical processing. After normalizing, the steel has equiaxed fine grains.
2. Quenching: The cylinder is heated to about 850 °C for quenching. The quenching medium can be selected according to the size of the steel and the hardenability of the steel. Generally, water or oil or even air quenching can be selected. The steel in the quenched state has low plasticity and large internal stress.
3. Tempering: =1 * GB3
1 In order to make the steel have high plasticity, toughness and appropriate strength, the steel is tempered at a high temperature of about 400-500 °C, and the steel which is sensitive to temper brittleness must be rapidly cooled after tempering to suppress the occurrence of temper brittleness. .
2 If the part is required to have a particularly high strength, it is tempered at about 200 ° C to obtain a medium carbon tempered martensite structure.
(2) Spring steel:
1. Quenching: oil quenching at 830-870 °C.
2. Tempering: returning with 420-520 °C to obtain tempered troostite structure.
(3) Carburized steel:
1. Carburizing: A type of chemical heat treatment in which a C element is penetrated into the surface of a steel member in an active medium containing a certain chemical element at a certain temperature. Preheating (850 ° C), carburizing (890 ° C), diffusion (840 ° C) process.
2, quenching: carbon and low alloy carburizing steel, generally using direct quenching or one quenching.
3. Tempering: low temperature tempering to eliminate internal stress and improve the strength and toughness of the carburized layer.
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