The design stress is increased, that is, by selecting a high-strength steel having a small diameter, the weight W of the coil spring can be reduced, thereby reducing the cost. As the valve springs improve with the performance requirements of the motorcycle, the requirements for material strength are also improved, and the materials and strengths are as shown. Material characteristics Strong éœ ç´ é’¢ä¸ é’¢ä¸ , , , , , , , , , , , , , , éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœ éœThe surface is strengthened by nitriding treatment.
To improve the fatigue properties of spring materials: 1) reduce non-metallic inclusions and surface defects; 2) refine austenite grains. Improve the elastic attenuation: 1) high strength of the spring material; 2) increase the tempering resistance of the steel. The effect of alloying elements on the strength of the tempered material is as shown. It shows the influence of strengthening elements such as C, Si and Cr on tensile strength.
Since the content of C in the steel is above 0.6%, the maximum quenching hardness is basically unchanged. The chemical composition of the quenched and tempered spring steel is generally 0.5% to 0.6%. Si, Cr is added to improve the elastic damping and quenching properties. Alloying elements such as Mn, usually used in a strength class of 180-1 lb X) Ml]a. The simplest way to increase the strength is to reduce the tempering temperature, but not simply to reduce the tempering temperature, but also to study the chemical composition.
In order to refine the grains, vanadium is added at the same time as increasing the carbon content. Vanadium is dispersed by VC to prevent coarse grains of austenite, and the secondary precipitation hardening of vanadium at tempering above 450 °C improves the resistance. Fire, which increases the strength, while Qin He Ni is also very effective in refining grains. The spring material can be integrally reinforced, or it can be surface treated by nitriding to increase the surface hardness and increase the surface compressive stress, thereby improving the fatigue life. The effect of alloying elements on nitriding hardness.
Since the nitriding treatment is a diffusion heat treatment, in order to improve the hardened layer, it is reasonable to increase the treatment temperature, but as the surface hardness is increased, the core hardness is lowered, and Mo and V are added to solve the problem to improve the tempering resistance. High-strength method of spring steel wire Part of the valve spring material is the high-carbon steel wire after drawing, mainly the oil tempering line treated by quenching and tempering, and the buffer spring is formed by cold-rolling with tempering line and hot-roll forming. .
Increase the amount of quenched 0.5-1.0 alloy added. Factors that hinder the improvement of strength With the increase of tensile strength, when a certain degree is reached, the tensile strength and the fatigue strength are out of proportion, due to inclusions and surface defects. It is known that the refinement of harmful inclusions is necessary to increase the fatigue strength under strength. Such as reducing the A12O3 system oxide, strengthening the surface quality inspection, controlling the surface decarburization during the manufacturing process are all conducive to improving the spring quality.
Free graphite destroys the continuity of the metal matrix, reduces the carbon content in the solid solution, affects the fatigue life of the spring, and free ferrite. The quenching heating temperature is low, the ferrite is not fully dissolved, and a mixture of martensite and ferrite appears after quenching. The presence of free ferrite reduces the strength and fatigue life of the spring; the microstructure is coarse.
The quenching temperature is too high to obtain coarse martensite and retained austenite. Large grain size will increase the brittleness of the material, causing the spring to break during use; feathery tissue. The quenching cooling rate can be low, and a feather-like bainite structure is formed; the band structure. There is a banded structure in the raw material, and there are still strip marks after quenching and tempering. This heterogeneity of the structure and composition will cause stress concentration in the local weak area, thereby reducing the fatigue life.
Microdestruction surface decarburization. The material is heated and annealed several times. If the protection is not good, the surface of the material often has decarburization, which will reduce the fatigue life of the material. 4 Springs and precautions when using the spring l) To ensure the uniformity of the internal structure of the material, the material should have enough The hardenability, considering the quality effect of the thermoformed coil spring, adding Cr to improve the hardenability; adjusting the tempering temperature can obtain different hardness, but the tempering temperature changes, other properties also change.
For example, when the quenching is insufficient, there is a large amount of retained austenite, and as the tempering temperature is increased, the austenite decomposition is reduced. The amount of austenite is large, the endurance is reduced, and the anti-elasticity is deteriorated; the cold-formed spring has residual stress due to the processing strain, and the low-temperature annealing is performed in order to eliminate residual stress and improve mechanical properties and fatigue strength. Low temperature annealing will reduce the material strength and fatigue strength, and choose a suitable low temperature annealing.
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