Stud heat treatment method for different materials and stud hardening process
March 25, 2019
Screw heat treatment, we also call the stud. The stud are divided into steel and stainless steel stud. Iron is generally harder if it needs to be harder. All need to be hardened. But stainless steel stud rarely need to be hardened. Because its hardness is enough, it is hard enough. The iron heat treatment method for iron is described below.
First, the heat treatment method: different heat treatment methods can be selected according to the object and 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: quenching after carburizing and then low temperature tempering (150-250 ° C)
After the low carbon and medium carbon (alloy) steels are quenched into martensite, the general rule is that the strength decreases and the plasticity and toughness increase as the tempering temperature increases. However, due to the different carbon content in low 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 separately:
(1) Select low-carbon (alloy) steel, and after quenching, temper at a low temperature of 250 ° C or lower 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 type of steel is quenched and tempered steel. If you want to get high strength, you would rather reduce plasticity and
Resilience, for low-temperature tempering of gold-containing tempering with low carbon content, the so-called "ultra-high-strength steel".
(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 elasticity At the limit, yield limit and fatigue limit, moderate temperature tempering after quenching is used.
Second, the operation process:
(1) Quenched and tempered steel:
1. Pre-heat treatment: normalizing->annealing (pearlite steel)->high temperature tempering (martensitic steel)
(1) 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 steel body 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) 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 tempering. Brittleness occurs.
(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: tempering at about 420-520 °C to obtain tempered troostite structure.
(3) Carburizing steel:
1. Carburizing: A type of chemical heat treatment in which a C element is infiltrated 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. The tempering temperature of the middle teeth of our company is about 360 °C, and the self-drilling screws (wall plate nails) have a tempering temperature of about 200 °C, and then cooled to 34-35 ° C and 39-40 ° C respectively.
Screw hardening, screw heat treatment, general screw SMEs, there will be no self-heating factory of the enterprise. Generally, it is necessary to send it to a professional screw and hard factory. Therefore, our company that produces screws attaches great importance to the choice of heat treatment plants. To choose a reasonable price, the quality of the screw after heat treatment is high quality.
