Comparison of popular steel grades for the manufacture of high-strength dowels: from Steel 45 to 30HGSA
What are the main requirements for the material of high-strength dowels?
The main requirements for the dowel material are a high yield strength to prevent plastic deformation and optimal hardness, ensuring a balance between the strength of the dowel itself and the safety of the mating parts. The choice of a specific steel grade depends on the nature of the transmitted torque and the operating conditions of the assembly (you can find out the options and characteristics of the materials in the catalog: https://zernotok22.ru/stal-shponochnaya/shponochny-prokat ).
The keyway connection, whether prismatic according to GOST 23360-78 or segmented according to GOST 24071-97, works as a key element in the transmission of torque from the shaft to the hub (gear, pulley, clutch). The material must resist destruction at peak loads, but at the same time often act as a mechanical fuse. Design engineers rely on the mechanical characteristics of the metal in their calculations, such as yield strength (σt), temporary tensile strength (σb) and hardness (HRC, HB). The wrong choice of material inevitably leads to a rapid failure of the entire mechanism, requiring expensive repairs by the chief mechanic.
What types of mechanical loads does the key experience during operation?
During operation, the key is subjected to two main types of loads: shear stresses (τ), which tend to destroy the part in cross-section between the shaft and the hub, and crumpling stresses (σcm), which affect its lateral faces. It is these forces that are the main causes of problems such as key cutting or keyway breaking.
When transmitting torque, half of the height of the prismatic dowel is in the shaft groove, and the other half is in the hub groove. The resulting force creates tremendous pressure on the contact surfaces. If the load is static, the risk of side edges crumpling prevails. Under dynamic, reversible, or impact loads (for example, in heavy machinery gearboxes or conveyor belts), the risk of fatigue failure and instantaneous shearing increases many times. Additionally, fretting corrosion may occur in joints with a gap, exacerbating surface wear.
Why are yield strength and hardness the main criteria for choosing steel?
The yield strength determines the load limit after which the dowel metal will begin to deform irreversibly, and the hardness is responsible for the surface's ability to resist crumpling and wear upon contact with the groove walls. These two parameters directly depend on the grade of carbon or alloy steel and the heat treatment performed.
If the yield strength (σt) of the selected material is