For iron and steel materials, due to the process of heating, deformation and cooling during forging, forgings exhibit different organization status due to material composition and forging size, and the following two points are mainly summarized.
1. Small and medium forgings (below 150kg) organization status This kind of forgings mainly uses the blank die forging forming of the rolling profile, for the hypoeutectoid (medium carbon steel, medium and low alloy structural steels), the coarse bulk ferrite and lamellar pearlite are generally obtained after the final forging, and the hypoeutectoid, especially the high carbon and high alloy steels, and the slow cooling after final forging are generally obtained.
Because of the difference of shape section of forgings and the uncontrollable cooling, the microstructure is often uneven, and due to the effect of temperature stress (also known as thermal stress) and tissue stress, the residual internal stress will be produced inside the forgings, so the heat treatment process must be used to improve and eliminate it.
2. Big forging organization State In 10MN from the above forging hydraulic press production of free forgings (shaft class parts greater than 5t, disk class parts greater than 2t)-like called forgings, such forgings are generally used ingot direct forging forming. Because of the forging, it heats more times (6 fire or more), due to the uneven deformation, large cross-section and high alloying degree, the most prominent feature of large forgings is the high residual hydrogen content and the serious organization heterogeneity (mixed crystal phenomenon), which is an important factor affecting the properties of large forgings. Therefore, it is important to solve the problem of heat treatment process design of large forgings.