Carbide Grain Boundary Rim
Carbide grain boundary film is a continuous or interrupted zone of carbides at the grain boundaries, which reduces the toughness and corrosion resistance of the steel. This film can arise from insufficient cooling or excessive carbon content.
Physical-Chemical Mechanism of Action
Carbide grain boundary film forms when carbides (like cementite) develop at the boundaries between different crystal grains of the steel. This process can be caused by insufficient cooling or excessive carbon content in the steel.
Metallurgical Relevance & Welding Risks
The carbide grain boundary film makes the weld joint more susceptible to intergranular corrosion and reduces its toughness. This can lead to cracking, wear, and reduced service life of components.
Shop Practice & Action Instructions
To avoid carbide grain boundary film, it is important to ensure careful cooling of the weld. This can be achieved by using cooling water or special cooling gases. A carbon content in the steel below 0.75% and adequate cooling time (t8/5 > 25 s) help to prevent the formation of this film.