If you cool low-alloy liquid steel containing approximately 0.08 wt% carbon below 1536 °C, solidification begins with the formation of a structure called delta ferrite (δ-ferrite). However, δ-ferrite has little significance in the design of structural steels. As the temperature drops further, say below 1400°C, δ-ferrite transforms completely into a structure known as austenite (γ).

Austenite (γ) is crucial in steel design because the manipulation of its crystal structure allows for the formation of various phases at different temperatures, leading to a wide range of mechanical properties in structural steels.

The crystal (or grain) of γ is often approximated as a honeycomb hexagonal prism. Picture (A) below is a partially re-austenitised low-alloy steel weld metal. It shows that γ crystals are indeed composed of hexagonal patterns.

Picture (B) shows a scanning electron micrograph of a housefly’s eye. Picture (C) is the magnified view of an area in the eye, revealing an area-filling hexagonal structure.

Thus, a common design is found in both living and nonliving things. Nature appears to favour hexagonal pattern in creating outstanding materials. We need to then connect the dots.

– Pictures from Cranfield University microscopy Lab