Primary Granular Solidification
Primary grain solidification is the process where grain formation occurs directly from the liquid melt. This leads to a homogeneous microstructure without prior phase formation.
Physical-Chemical Mechanism of Action
Primary grain solidification starts as soon as the melt cools below its melting point. A crystal lattice forms directly from the liquid phase without intermediate phases such as a metal carbonate phase. This process is especially typical for high-purity steels or alloys with low zinc and nickel content.
Metallurgical Relevance & Welding Risks
Primary grain solidification results in a homogeneous microstructure that offers excellent mechanical properties like high strength and toughness. However, it can also lead to increased hardness and susceptibility to hot cracking, especially if cooling is too fast. This can cause weld defects like splatters or fractures.
Workshop Practice & Action Guidelines
To achieve primary grain solidification and minimize risks, it is important to control the cooling of the weld. This can be done using cooling water or special coolants. The optimal cooling rate depends on the material and the desired microstructure, but in general, cooling should be slow to ensure homogeneous solidification.