Steel microstructure

A nitric-acid/alcohol metallographic etchant. In pearlitic steel it can preferentially remove ferrite, leaving cementite standing higher. In an atomic force microscopy height image, darker then means lower surface height, not an optical reflectivity or atomic-number contrast.

Heating quenched steel below the austenitizing range to adjust its microstructure and relieve stresses. Carbon redistribution and carbide formation can improve toughness at a cost in hardness.

A microstructure in which carbon redistribution and carbide formation reduce the supersaturation of a martensitic matrix. Plate or lath morphology can remain while local strain and thermodynamic phase composition evolve. The term describes a material state, not a universal guarantee of a particular toughness.

A chart of the time needed to reach specified transformation fractions after cooling to, and holding at, a fixed temperature. Its curves are not themselves continuous-cooling histories; estimating a critical cooling rate from their nose is an approximation.

A product of a displacive transformation. In carbon steel, rapid cooling can trap carbon in a distorted iron lattice, producing high hardness and low as-quenched toughness.

A lamellar two-phase microconstituent of ferrite and cementite, rather than a single thermodynamic phase. Shorter diffusion distances at greater undercooling generally produce finer lamellae before diffusional transformation is bypassed.

The proportions of ferrite and cementite within the two-phase pearlite microstructure. A lever rule on a weight-percent-carbon diagram gives mass fractions; converting those to volume fractions requires the phase densities. Proeutectoid phases outside pearlite must be treated separately.

The face-centred cubic iron-rich solid phase of steel. Its transformation products depend on composition and cooling history.

The body-centred cubic iron-rich solid phase of ordinary low-temperature steel, with low equilibrium carbon solubility.