Microstructural inhomogeneity
Microstructural inhomogeneity is an uneven distribution of alloying elements and phases within the metal, caused by non-uniform cooling or incomplete penetration. It leads to varying properties such as hardness and strength in different areas.
Physical-chemical mechanism
Microstructural inhomogeneity occurs when during welding certain areas cool faster or slower than others. This leads to different crystal forms and sizes, which in turn affects mechanical properties.
Metallurgical relevance & risks in welding
Microstructural inhomogeneity can cause local hardness variations, leading to cracks or distortion. It can also impair toughness and stress-bearing capacity, which can be dangerous particularly in highly stressed applications.
Workshop practice & instructions
To minimize microstructural inhomogeneity, it is important to ensure uniform cooling. This can be achieved using cooling water or gas. The weld should not cool too quickly (t8/5 > 25 s) to ensure homogeneous structure development. For heavy steels, it is also helpful to temper the weld in an oven before cooling.