Analysis on heat treatment process of large castings by induction heating machine

Due to the relatively poor plasticity and toughness of large castings, uneven and compact internal structures, and complex shapes, the technical requirements for castings are also different in different environments. In the process of heat treatment of large castings, we usually use induction heating machines to reduce the internal stress of castings and prevent surface cracks and cracks. The heat treatment process for large castings often includes preparatory heat treatment, normalizing and tempering heat treatment, annealing treatment, quenching and tempering treatment, stress relief annealing treatment, etc., and different processes have different effects.

Preparatory heat treatment is also called high-temperature annealing. Its function is to eliminate and reduce the precipitation of components in the casting, improve the material, and ensure that the internal structure and mechanical properties of the casting are uniform and stable. Normalizing and tempering heat treatment is to refine the internal structure of the casting, improve its strength, toughness and machinability, and ensure that the mechanical properties of the casting can meet the technical requirements. After the casting is formed, in order to eliminate its internal stress, it is usually annealed to improve the size, structure and performance of the casting, and the annealing process is simple to operate and will not affect subsequent use. If the technical performance requirements of some castings are particularly high, it is necessary to use an induction heating machine to quench and temper them, but it should be noted that the castings must be fully annealed before quenching and tempering. If some large castings are welded castings or after rough machining, they need to be treated with stress relief annealing to eliminate internal stress in the casting and stabilize the size.

In the process of heat treatment of large castings, the more common disadvantage is cracking, especially in some key positions, such as corners and the position of section thickness, which are easy to concentrate stress, which is caused by tensile stress, called external cracking. For example, the inside or shrinkage of the casting is caused by internal stress, which is called internal cracking. In this regard, we can heat-treat castings through induction heating machines according to actual conditions to reduce or avoid cracks, improve mechanical properties, and prolong service life.