Widmanstätten ferrite
Widmanstätten ferrite forms during rapid cooling from austenite, with ferrite plates growing along the austenite planes. This leads to increased brittleness and reduced strength levels.
Physical-chemical mechanism of action
Widmannstätten ferrite forms when an austenitic structure cools rapidly. The fast cooling prevents complete transformation into pearlite. Instead, a glassy ferrite structure forms from crystallographically aligned crystals that grow along the austenite planes.
Metallurgical relevance & risks in welding
The formation of Widmannstätten ferrite leads to increased brittleness and reduced strength of the steel. This can cause cracking and fracture under mechanical stress. Furthermore, brittleness can make welding more difficult because the metal is harder to work with.
Shop practice & action items
To avoid Widmannstätten ferrite, the cooling of the steel should be slow and controlled. This can be achieved by using cooling water or cooling oil. When welding, it's important to ensure adequate post-weld time to stabilize the structure. Recommended cooling times vary by steel type and can range from 10 to 60 minutes.