Polycrystal
A material consists of many small, randomly oriented crystals. Properties depend on grain size and grain boundaries.
Physical-Chemical Mechanism of Action
A polycrystal is made up of many small crystals that are randomly oriented. These crystals are called crystallites or grains. The overall properties of the material are influenced by the size and arrangement of these grains.
Metallurgical Relevance & Risks in Welding
Grain size and grain boundaries affect mechanical properties such as strength, fatigue life, and toughness. Grains that are too large can lead to poorer mechanical properties, while a fine crystal structure offers better properties. During welding, the structure can coarsen (grain coarsening), which can degrade mechanical properties.
Workshop Practice & Action Guidelines
To get a good crystal structure, it's important to control the melting process well. This includes choosing the right welding process, correct temperature and cooling time, and using deoxidizers. For heavy steels or high mechanical demands, a fine crystal structure is especially important.