Grain size

Grain size
The relationship between the strength and plasticity of the metal and the grain size.
Strength: There is a Holpeci formula. The strength of the material becomes stronger as the grain size becomes smaller, and the temperature rise strength is greatly reduced. However, this formula is not applicable at the time of nano-grain, and the strength of the nanocrystal is enhanced more. However, the strength of a single crystal does not follow the above rules, the strength of a single crystal is very strong, and it can maintain a strong strength at high temperatures.
Plasticity: In a certain volume of crystal, the more the number of crystal grains, the more grain boundaries, the finer the crystal grains, and the more grains in different orientations, the greater the resistance to plastic deformation. Fine crystal The polycrystalline crystals of the particles are not only high in strength, but also good in plasticity and toughness. Because the finer the crystal grains, the deformation amount can be dispersed more under the same changing conditions.
Method of refining grains
1, solidification control, including grain refiner (generally an intermediate alloy), grain refining elements;
Shorten the setting time, this can't be too much, too much will produce amorphous;
In the solidification process, external force physical fine crystals such as electromagnetic stirring are applied.
2, already ingots, forging fine grains (this method can prepare nanocrystals under certain conditions, participate in the corresponding article of Academician Lu Ke); cold working rolling can refine grains in the rolling direction, and then Crystallization can also refine grains.
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