Quality Requirement of Wire for Vehicle Suspension Spring
Release Time:
Dec 21,2023
The wire rod for car suspension spring has strict requirements on the purity, dimensional accuracy and surface quality of steel. Practice has proved that the diameter accuracy of wire rod is of great significance to reduce wire drawing die wear, reduce energy consumption, reduce wire breakage and ensure stable drawing. The diameter tolerance of wire rod for suspension spring shall be controlled within ± 0.2mm, and the ovality shall not be greater than 60% of the diameter tolerance. The cracks, folds, scratches and other defects on the surface of the wire seriously affect the quality of the wire and reduce the fatigue life of the suspension spring. The wire surface shall be smooth and free from cracks, folds, scarring, ears, etc. The size of local defects such as bumps, pits and pockmarks shall not be greater than 0.10mm. The mechanical properties of the wire rod are better, and the fluctuation is small. The tensile strength fluctuation of the wire rod is less than or equal to 40MPa, the area shrinkage fluctuation is less than or equal to 15%, the volume fraction of sorbite is more than or equal to 85%, the free ferrite has a great influence on the fatigue life, the volume fraction should be controlled within 1.5, the grain size is above 8, and no martensite is allowed.
The wire rod for car suspension spring has strict requirements on the purity, dimensional accuracy and surface quality of steel. Practice has proved that the diameter accuracy of wire rod is of great significance to reduce wire drawing die wear, reduce energy consumption, reduce wire breakage and ensure stable drawing. The diameter tolerance of wire rod for suspension spring shall be controlled within ± 0.2mm, and the ovality shall not be greater than 60% of the diameter tolerance. The cracks, folds, scratches and other defects on the surface of the wire seriously affect the quality of the wire and reduce the fatigue life of the suspension spring. The wire surface shall be smooth and free from cracks, folds, scarring, ears, etc. The size of local defects such as bumps, pits and pockmarks shall not be greater than 0.10mm. The mechanical properties of the wire rod are better, and the fluctuation is small. The tensile strength fluctuation of the wire rod is less than or equal to 40MPa, the area shrinkage fluctuation is less than or equal to 15%, the volume fraction of sorbite is more than or equal to 85%, the free ferrite has a great influence on the fatigue life, the volume fraction should be controlled within 1.5, the grain size is above 8, and no martensite is allowed.
As a fatigue crack source, inclusions can cause fatigue crack propagation and lead to spring fracture, which has become one of the main reasons for spring failure. Especially for springs used under high pressure stress conditions, the relationship between fatigue limit and hardness is no longer linear. When the hardness HV value of the material exceeds 400, microinclusions will become the source of fatigue cracks, which will reduce the fatigue limit of the material. However, automobile suspension springs are usually used when the HV value is 430~535, which requires no brittle inclusions greater than 15μm.
Surface decarburization will cause the decrease of surface hardness, and it is easy to form surface fatigue crack source in processing, which has an important influence on the fatigue life of suspension spring. It is required that the total decarburized layer on the surface of the wire rod is not more than 1% of the nominal diameter of the wire rod to avoid complete decarburization.
The fluctuation of carbon content will cause the fluctuation of mechanical properties: carbon content is positively correlated with tensile strength and negatively correlated with section shrinkage. Reducing carbon content can reduce decarburization, improve formability and resistance to elastic reduction. The fluctuation range of carbon mass fraction should be less than 0.03%. Silicon has a high solid solution strengthening effect, which is beneficial to improve the resistance to elastic reduction, and too high silicon content is easy to form silicate inclusions and decarburization tendency. Manganese can strengthen the strength and hardenability of the spring, but it also increases the overheating sensitivity and temper brittleness of the steel. For example, in high-quality 55SiCr, the mass fraction of silicon is generally 1.33 to 1.45, and the mass fraction of manganese is 0.67 to 0.69. The content of sulfur and phosphorus should be strictly controlled. High-quality suspension spring products require the mass fraction of sulfur and phosphorus to be less than 0.01 and 0.015, respectively, the mass fraction of oxygen ≤ 15 × 10, and the mass fraction of nitrogen ≤ 35 × 10.
Through the understanding of the current products, we can also know that the spring manufacturers are strict in the process of manufacturing various springs such as curved springs, and they are not able to meet the demand of the products for springs.
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