Ferritic grain boundary network
Ferritic grain boundary network forms by ferritic crystals arranging parallel to austenite grain boundaries during undercooling. It affects the toughness and hardness of the steel.
Physico-Chemical Mechanism of Action
During cooling of austenite, a network of ferritic crystals forms, arranged parallel to the previous austenite grain boundaries. This process occurs through diffusion-controlled transformation of the austenitic structure into ferritic.
Metallurgical Relevance & Risks in Welding
A strong ferritic grain boundary network can increase toughness because it promotes finer grain. However, it can also lead to increased susceptibility to hot cracking if the network is too dense and too brittle. This can occur especially under high loads and temperatures.
Workshop Practice & Action Guidelines
To create an optimal ferritic grain boundary network, the undercooling rate should be controlled. Too fast undercooling can lead to a too brittle structure (t8/5 < 5 s), while too slow undercooling results in too coarse grain and low toughness (t8/5 > 25 s). Correct heat treatment is crucial to achieve the desired mechanical properties.