Grain boundary ferrite
Grain boundary ferrite forms during cooling at the prior austenite grain boundaries and can form continuous networks, which reduces the material's toughness. This occurs due to a finer crystal structure and an increased number of interfaces.
Physicochemical Mechanism of Action
Grain boundary ferrite forms when austenite transforms to ferrite at the grain boundaries between different grain sizes during cooling. This process can lead to continuous networks that have a finer crystal structure and more interfaces.
Metallurgical Relevance & Risks in Welding
The formation of grain boundary ferrite can reduce the material's toughness, as continuous networks have lower hardness and toughness than open structures. This increases the risk of cracking and deformation.
Workshop Practice & Action Guidelines
To avoid grain boundary ferrite, control the cooling rate during welding. Too rapid cooling can cause austenite to transform to ferrite at the grain boundaries. Cool the weld slowly and evenly, for example by using cooling water or a shielded environment.