What effect does the grain size of a metal have on the metal?

When a metal crystallizes, it is a polycrystal composed of many grains. The grain size can be expressed by the number of grains in a unit volume. The higher the number, the smaller the grain size. The number of grains per unit cross section or the average diameter of the grains is often used for measurement purposes. The grain size of a metal has a significant effect on many properties of the metal. The effect of tungsten carbide grain size is essentially the effect of the size of the grain boundary area. The finer the grain size of tungsten carbide, the larger the grain boundary area and the greater the effect on properties. For the room temperature mechanical properties of metals, generally the finer the grain, the higher the strength and hardness, while plasticity and toughness is also better. This is because, the finer the grain, the more plastic deformation can also be dispersed in more grains, so that the more uniform plastic
deformation, the smaller the concentration of internal stress; and the finer the grain, the more crystal interface, the more curved grain boundaries; the more opportunities for interlocking grains and grains, the more adverse to the propagation and development of cracks, the tighter each other, the better the strength and toughness. Table lists the effect of grain size on the mechanical properties of pure iron. From the table can be seen to refine the grain to improve the mechanical properties of the metal at room temperature plays a big role, therefore, usually always hope that the tungsten carbide products material the finer the grain the better.

But in the high-temperature work of metal materials, the grain is too large or too small are not good. Therefore, usually want to get a moderate grain size, but in some cases hope that the grain is coarser and larger the better. For example, the manufacture of electric motors and transformers is such a silicon steel sheet, the coarser the grain, the smaller the tape loss, the higher the efficiency. In short, the impact of grain size on metal performance is multifaceted, to specific analysis of the specific situation