What Material Are Automotive Leaf Springs Made Of?

[DePatrick]

Automotive leaf springs are manufactured using materials such as 60Si2Mn and 50CrV, through processes including blanking, drilling, eye rolling, quenching, tempering, shot peening, assembly, preloading, and painting. Also known as laminated springs or simply "leaf springs," they consist of multiple steel plates of varying lengths and curvatures stacked together, which naturally curve upward at both ends after installation. The function of automotive leaf springs is to absorb and mitigate road impacts on the wheels through deformation, providing cushioning and shock absorption. When arranged longitudinally, they also serve to guide and transmit forces.

[OAngelina]

I've been repairing vehicles for over a decade and have disassembled numerous truck chassis. Most leaf springs are made of 60Si2Mn manganese-silicon alloy steel, with silicon added to enhance elasticity and manganese to increase hardness. For heavy-duty trucks, 55CrMnA steel containing chromium is used to improve wear resistance. These steel plates must undergo quenching and tempering treatments before leaving the factory to ensure both flexibility and pressure resistance. The rear axles of 5-ton trucks typically stack seven or eight steel plates, each requiring shot peening reinforcement to withstand repeated bending. Last time when helping a logistics fleet replace rear suspensions, I found the fractured old leaf springs were caused by material inhomogeneity leading to stress concentration. I recommend owners inspect leaf spring surface cracks every two years, especially for vehicles frequently driven on mountain roads.

[LaPiper]

In the field of mechanical engineering, the alloy formulation of spring steel is quite particular. It starts with high-quality carbon steel, with 1-2% silicon and manganese added to enhance toughness, while chromium and vanadium elements improve fatigue strength. For example, the SUP6 spring steel commonly used in Japanese cars contains 0.6% carbon, achieving a tensile strength of over 1500 MPa after heat treatment. Interestingly, the manufacturing process is relatively simple: after hot rolling into shape, it is coiled into a semicircle, and the cooling rate is controlled during high-temperature oil quenching to prevent distortion. Nowadays, some buses are experimenting with composite leaf springs, but trucks still rely on steel leaf springs—after all, when twenty tons of cargo comes crashing down, the metallic bonds between steel molecules are best at withstanding impact loads.

[Margot]

Three common spring steel plate materials in the auto parts market: 55SiMn hot-rolled steel offers high cost performance; 50CrVA chromium-vanadium alloy steel has strong fatigue resistance; 60Si2CrVA vanadium-containing steel used in heavy trucks is more wear-resistant. Some off-road enthusiasts replace their pickup truck springs with Japanese JIS SUP9 spring steel, which shows noticeably better flexibility when crossing speed bumps. Pay attention to decarburization at the steel plate edges - the oxide scale generated during oxygen cutting can reduce strength by 20%. Last time when customizing a lift kit for an off-road club, we specifically requested continuously rolled whole-piece steel to avoid weld joint fractures in desert sections. Regularly applying graphite grease between steel plate leaves can reduce squeaking noises.