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Quality requirements for wire rods for vehicle suspension springs

Number of visits: Date:1/3/2017

Car suspension spring with steel on the purity of steel, dimensional accuracy, surface quality has strict requirements. Practice has proved that the diameter of the wire diameter to reduce the drawing die wear, reduce energy consumption, reduce broken wire, to ensure the stability of drawing is of great significance. The diameter tolerance of the wire for the suspension spring is controlled at ± 0.2 mm and the ellipticity is not greater than 60% of the diameter tolerance. Wire surface cracks, folding, scratches and other defects seriously affect the quality of the wire, reducing the fatigue life of the suspension spring. Wire surface should be smooth, no cracks, folding, scarring, ears and so on. Local bumps, pits, hemp and other defects in the size of not more than 0.10mm. The mechanical properties of the wire are better and the fluctuation is small. The tensile strength fluctuation of the wire rod is less than or equal to 40MPa, the shrinkage of the section is less than or equal to 15%, the volume fraction of sorbite is ≥85%, the free ferrite has a great influence on the fatigue life, the volume fraction should be controlled within 1.5% Degree of 8 or more, no martensite.
Inclusions as a fatigue crack source will lead to fatigue crack expansion, and ultimately lead to spring breakage, it caused the spring failure has become one of the main reasons for spring damage. Especially in the high-pressure stress conditions used under the spring, the fatigue limit and hardness is no longer a linear relationship between the material hardness HV value of more than 400 after the micro-inclusions will become a fatigue crack source, the material fatigue limit decreased Automotive suspension springs are usually used at HV values ​​of 430 to 535, requiring no brittle inclusions greater than 15 μm.
Surface decarburization can cause the surface hardness to decrease, easy to form in the process of surface fatigue crack source, the suspension spring fatigue life has an important impact. It is required that the total decarburization layer on the wire surface is not more than 1% of the nominal diameter of the wire and avoid the whole decarburization.
Carbon content fluctuations, will cause mechanical properties of fluctuations: carbon content and tensile strength is positively correlated with the negative shrinkage of the cross-section, reduce carbon content can reduce decarburization, improve the formability and anti-buckling. The fluctuation range of carbon mass fraction should be less than 0.03%. Silicon element has a high solid solution strengthening effect, to improve the anti-buck life advantage, high silicon content is easy to form silicate inclusions and produce decarburization tendency. Manganese can enhance the strength and hardenability of the spring, but also increases the overheating sensitivity of the steel and temper brittleness. Such as high quality 55SiCr, the silicon mass fraction is generally 1.33% ~ 1.45%, manganese mass fraction of 0.67% ~ 0.69%. Sulfur and phosphorus content should be strictly controlled, high-quality suspension spring products require sulfur and phosphorus mass fraction of less than 0.01% and 0.015%, oxygen mass fraction ≤ 15 × 10, nitrogen mass fraction ≤ 35 × 10.
Through the understanding of the product, you can also know the spring manufacturers in the manufacture of various springs such as bending the spring process is strictly required, not to reach the product of the spring demand.

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