Microstructural Inhomogeneity of the Heat-Affected Zone
Different microstructure zones arise in the heat-affected zone due to local temperature peaks, leading to varying hardness and toughness values.
Physicochemical Mechanism of Action
Welding processes change the microstructure of the metal near the weld. Local temperature peaks during cooling can lead to different microstructural zones, such as martensite or austenite. These different zones have different properties like hardness and toughness.
Metallurgical Relevance & Risks in Welding
Microstructural inhomogeneity can cause uneven mechanical properties, which poses risks to component integrity. Stronger zones can cause cracks or make the material more susceptible to mechanical stress. Additionally, stress concentrations can occur, which can lead to corrosion.
Workshop Practice & Action Instructions
To minimize microstructural inhomogeneity, controlled cooling is crucial. This can be achieved by using cooling water or special cooling gases. The cooling rate should be set so that the material cools evenly and no local temperature peaks occur. For difficult-to-deform steels, slow cooling (t8/5 > 25 s) is recommended to ensure a homogeneous microstructure.