Cementite Lamellar Spacing
The spacing between adjacent cementite lamellae in pearlitic structure affects the hardness and yield strength of the steel. It results from diffusion conditions during the eutectoid transformation.
Physical-Chemical Mechanism of Action
Zementite lamellae form through the eutectoid transformation of austenite to pearlite. During this transformation, carbon and iron diffuse toward each other, forming lamellae of cementite. The spacing between these lamellae depends on the diffusion rates.
Metallurgical Relevance & Welding Risks
Too large a spacing of the cementite lamellae leads to increased hardness and yield strength of the steel, which reduces formability. Conversely, too small a spacing can result in lower hardness and higher formability. During welding, uneven growth of the lamellae can cause stresses that may lead to cracking.
Workshop Practice & Action Instructions
To ensure an optimal cementite lamellae structure, the weld pool should be well protected from oxygen to allow homogeneous diffusion. The cooling rate should be controlled to make the eutectoid transformation proceed uniformly. When selecting the steel, make sure the desired lamellae spacing is achieved to get the required mechanical properties.