Spring steel features a spring mainly works under dynamic load, that is, under the conditions of shock, vibration, or work under the effect of alternating stress, the use of elastic deformation to absorb shock energy, play a buffering role.
As the spring is often subjected to vibration and long-term work under the action of hedonic stress, mainly fatigue damage, so the spring steel must have a high elastic limit and high fatigue limit. In addition, there should be sufficient toughness and plasticity to prevent sudden brittle breakage under the action of impact.
In the process theory, the spring steel should have good hardenability and low overheating, decarburization sensitivity. Reduce the surface roughness of the spring can improve fatigue life.
In order to obtain the required performance, spring steel must have a high carbon content. Carbon spring steel carbon content between 0.6-0.9%, due to the poor hardenability of carbon spring steel, so only used in the manufacture of cross-sectional dimensions of not more than 10-15mm spring. For springs with larger cross-sectional dimensions, alloy spring steel must be used. Alloy spring steel carbon content between 0.45-0.75%, the addition of alloying elements are Mn
Si, W, V, Mo and so on. Their main role is to improve the hardenability and tempering stability, strengthen the ferrite and refine the grain, effectively improving the mechanical properties of spring steel, which Cr, W, Mo can also improve the high-temperature strength of steel.
Spring formed in the hot state (diameter or thickness is generally more than 10mm)
Springs formed in the cold state (diameter or thickness generally below 10mm)
Heat treatment process for hot formed springs - Most springs formed in this way combine hot forming and heat treatment, while most coil springs are heat treated after hot forming. The heat treatment of this type of spring steel is quenching + tempering at medium temperature, and the organization after heat treatment is tempered taustenite. The elastic limit and yield limit of this organization are high, and there is a certain degree of toughness.
Cold-formed spring heat treatment process - for cold-rolled steel, steel strip or cold-drawn steel wire made of spring, due to cold plastic deformation to strengthen the material, it has reached the performance required by the spring. Therefore, the spring is formed only in the range of about 250C, holding about 30min of stress relief treatment to eliminate the cold forming spring door stress, and the spring can be shaped.
Heat treatment of heat-resistant spring steel - internal combustion engine valve springs are working at higher temperatures, some also have a corrosive atmosphere, so you must choose a special spring steel and appropriate heat treatment specifications.