The grain size of forgings refers to the average area or average diameter of the grains in the forgings. What factors affect the grain size of forgings?

The main mechanical properties of coarse-grained forgings are plasticity and toughness, which are significantly lower than those of fine-grained forgings. Refining grains by heat treatment is not only labor-intensive and costly, but also extremely difficult or even impossible for some alloy steels. Therefore, it is necessary to formulate a reasonable forging process for certain steel grades based on the recrystallization diagram of hot working. The higher the forging temperature, the larger the grain size of the forging after recrystallization. Therefore, under the condition that the forgings do not produce low-temperature forging cracks, the final forging temperature should be reduced as much as possible to ensure grain refinement. However, for large forgings, it is very difficult to ensure that all parts of the same forging use the same low final forging temperature, which can only rely on the experience and skills of the forging master.

At a certain forging temperature, there is a critical deformation range. When the deformation degree is within this range, the recrystallized grains of the forging are relatively coarse. Therefore, during forging, especially the last fire, the deformation degree should be avoided within the critical deformation degree as much as possible.