The coil element, also known as wire or coil material, is made by heating and rolling steel billets. (Hot-rolled wire rod cannot be used for the production of fasteners due to its size and surface quality, and must be reprocessed)
Annealing: A metal heat treatment process that slowly heats a metal to a certain temperature, holds it for a sufficient time, and then cools it at a suitable rate (usually slow cooling, sometimes controlled cooling).
The purpose is to soften the material or workpiece after casting, forging, welding, or cutting, improve the plasticity and toughness, homogenize the chemical composition, remove the residual stress, or obtain the expected physical properties. There are a variety of annealing processes depending on the purpose, such as recrystallization annealing, isothermal annealing, homogenization annealing, spheroidizing annealing, stress relief annealing, recrystallization annealing, and stabilization annealing, magnetic field annealing, and so on.
Spheroidizing annealing—Spheroidizing carbides, the material is plastic. The steel is heated to 20-30 ° C above Ac1, held for a period of time, and then slowly cooled to obtain a spherical or granular carbide structure uniformly distributed on the ferrite matrix.
Steel is air-cooled after rolling and forging. The resulting structure is lamellar pearlite and reticulated cementite. This structure is hard and brittle, not only difficult to cut, but also easily deformed and cracked in the subsequent quenching process.
Spheroidized pearlite structure is obtained through spheroidizing annealing. The cementite is spherical particles dispersed on the ferrite matrix. Compared with flaky pearlite, it has lower hardness and is easier to cut and hardened. When heated, austenite grains are not easy to grow, and the workpiece has a small tendency to deform and crack when cooled.
Examine the spheroidizing structure and decarburized layer to confirm the spheroidizing effect.