Crystallite
A crystallite is a region in a material with uniform lattice structure and the same orientation. Many crystallites form the macroscopic grain structure.
Physicochemical Mechanism of Action
A crystallite is a region within a material where atoms are arranged in a regular lattice pattern. This lattice is homogeneous and undisturbed throughout the entire area of the crystallite.
Metallurgical Relevance & Welding Risks
The size and number of crystallites affect the mechanical properties of a material. Small crystallites lead to higher strength and toughness, but also to greater stresses during cooling. This can cause cracks or hot cracks. Large crystallites make the steel softer and lose hardness.
Workshop Practice & Instructions
To control crystallite sizes in the weld, cooling is regulated. Fast cooling (short t8/5) can produce small crystallites and increase hardness, while slow cooling (long t8/5) forms large crystallites and increases toughness. For steel types like martensite, a fast cooling method is necessary to avoid glass-hard structures.