Weld Toe
The weld toe is the transition area between the fused weld and the unchanged base material. Here, special metallurgical phenomena occur, such as hardening, segregation, and embrittlement.
Physico-chemical mechanism
The weld edge forms as the molten pool cools. Metal atoms condense and form a new structure that differs from the base material. Temperature gradients in this zone lead to various phenomena such as hardening (too hard grains), segregation (too soft grains), or embrittlement (too many small grains).
Metallurgical relevance & risks when welding
The special metallurgical phenomena at the weld edge can cause several problems. Hardening can lead to crack-sensitive structures, reducing mechanical strength. Segregation increases toughness but can also cause stress concentrations and hot cracking. Embrittlement can produce fine grains, making the weld softer and lowering its mechanical strength.
Workshop practice & instructions
To improve the quality of the weld edge, it is important to control cooling conditions and the cooling pattern precisely. Use an appropriate cooling medium temperature and ensure the weld does not cool too fast or too slow. For high-carbon steel (e.g., HSS), it is especially important to maintain the t8/5 time between 5 and 25 seconds to achieve a balanced structure.