For steel materials, due to the heating, deformation and cooling processes during forging, the wheel forgings show different structures due to the material composition and the size of the wheel forgings. In summary, there are two main points.
1. Organizational status of small and medium wheel forgings
This type of wheel forgings is mainly formed by die forging of rolled profiles. For hypoeutectoid steels (medium carbon steel, medium carbon low alloy structural steel), when it is air-cooled to room temperature after final forging, generally coarse lump ferrite and Lamellar pearlite structure; For hypereutectoid steels, especially high-carbon and high-alloy steels, slow cooling after final forging can generally obtain a relatively coarse annealed structure. Because of the difference in the shape and cross section of the wheel forging and the uncontrollable cooling, its structure is often uneven, and due to the effects of temperature stress (also known as thermal stress) and tissue stress, residual internal stress will be generated in the wheel forging, so it must be treated by heat treatment. Improve and eliminate.
2. Organization status of large wheel forgings
This type of wheel forging is generally formed by direct forging of steel ingots. During forging, the number of heating times (6 fires or more), uneven deformation, large cross-section differences, and high degree of alloying of materials, the most prominent characteristics of large wheel forgings are high residual hydrogen content and serious non-uniformity. Existence (mixed crystal phenomenon). This is an important factor affecting the performance of wheel forgings, and therefore it is also a problem that needs to be addressed in the design of heat treatment process for wheel forgings.