Definition Of Common Heat Treatment Terms

Allotropy :   The ability of a material to exist in more than one crystalline form. Steel has a BCC form when cold but exists as FCC austenite when heated above the upper

                        critical temperature.

Pearlite :   A mixture of alternate layers of ferrite and cementite. It is mostly ferrite and gives off a sheen similar to mother of pearl. Pearlite is formed at 0.83% carbon.

BCC structure:   Atoms are arranged so that their centres are positioned at the corner of a cube, with one atom in the centre of the cube. This structure is associated with brittleness in metals.

FCC structure:   Atoms are arranged so that their centres are positioned at the corners of a cube, with one atom at the centre of each face of the cube. In this structure atoms are more tightly packed which facilitates ductility in metals.

Simple Eutectic:   The two metals are completely soluble in the liquid state but insoluble in the solid state. On cooling, two separate types of crystals or grains are formed.

Solid solution:   When two metals are completely soluble in each other in both the liquid and solid states. When the alloy solidifies only one type of crystal is formed and it looks like a pure metal.

Dendritic Growth :  A dendrite is a crystal with a tree-like branching structure. In the current context, we are interested in metallic dendrites formed when a metal, or an alloy of multiple metals, in liquid form solidifies. Other materials when frozen form crystals consisting of dendritic (tree-like) branches, the most familiar example being snowflakes.

Vacancies : a vacancy is a type of point defect in a crystal.  Crystals inherently possess imperfections, often referred to as 'crystalline defects'. A defect wherein an atom, such as silicon, is missing from one of the lattice sites is known as a 'vacancy' defect. Simply put it is a missing atom in the crystal lattice.

A Dislocation is a crystallographic defect or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials

Ferrite also known as α-ferrite (α-Fe) or alpha iron is a materials science term for iron, or a solid solution with iron as the main constituent, with a body-centered cubic crystal structure. Practically speaking, it can be considered pure iron