Grain refinement mechanism
The grain refinement mechanism creates many small crystal grains by using alloying additions as nuclei. This prevents the growth of large grain boundaries and increases the strength and toughness of the material.
Physical-Chemical Mechanism
Alloying additions such as silicon or titanium act as crystallization nuclei. These nuclei promote the splitting of large crystals into many small ones, which reduces the overall size of the grain boundaries.
Metallurgical Relevance & Risks in Welding
A fine grain structure (small crystal grains) increases the strength and toughness of the material. It also prevents cracks and improves mechanical properties. However, an overly coarse grain structure can lead to low toughness and higher susceptibility to cracking.
Workshop Practice & Action Instructions
To utilize the grain refinement mechanism, additional alloying additions are introduced into the weld pool. The temperature and solidification time must be precisely controlled to achieve optimum grain refinement. A typical target is a crystal grain size of 10–20 µm.