As-Cast Microstructure
Cast structure forms by rapid cooling in the weld pool and shows segregations and coarse grain. It is the primary solidification structure before any post-treatment.
Physicochemical mechanism of action
The cast structure forms when the metal casting cools rapidly and transforms into a solid. This rapid cooling process prevents the formation of fine crystals and leads to coarse grain and segregations in the material.
Metallurgical relevance & risks during welding
A good cast structure is crucial for a good weld, as it provides a homogeneous base. If the cast structure is too coarse or uneven, it can lead to weak points and cracks in the weld. Also, rapid cooling can cause high hardness of the material, making it harder to shape during welding.
Workshop practice & instructions for use
To ensure a good cast structure, the cooling in the weld pool should be controlled and slow. This can be achieved by using cooling water or cooling gas. A typical goal is a cooling duration of at least 10 minutes per cm³ of cast volume to prevent the growth of coarse crystals and create a homogeneous cast structure.