Steel Terminology

Terminology

In metallurgy, one may encounter many terms that have very specific meanings within the field, but may seem rather vague when viewed from outside. Terms such as "hardness," "impact resistance," "toughness," and "strength" can carry many different connotations, making it sometimes difficult to discern the specific meaning. Some of the terms encountered, and their specific definitions are:

Strength: Also called rigidity, this is resistance to permanent deformation. Strength, in metallurgy, is still a rather vague term, so is usually divided into yield strength (resistance to compression), shear strength (resistance to transverse, or cutting forces), and tensile strength (resistance to stretching).

Toughness: Resistance to fracture, as measured by the Charpy test. Toughness often increases as strength decreases.

Hardness: Hardness is often used to describe strength or rigidity but, in metallurgy, the term is usually used to describe resistance to scratching or abrasion.

Brittleness: Brittleness describes a material's tendency to break before bending or deforming either elastically or plastically. Brittleness increases with decreased toughness, but is greatly affected by internal stresses as well.

Plasticity: The ability to mold, bend or deform in a manner that does not spontaneously return to its original shape. This is proportional to the ductility or malleability of the substance.

Elasticity: Also called flexibility, this is the ability to deform, bend, compress, or stretch and return to the original shape once the external stress is removed. Elasticity is related to the Young's modulus of the material.

Impact resistance: Usually synonymous with high-strength toughness, it is the ability resist shock-loading with minimal deformation.

Wear resistance: Usually synonymous with hardness, this is resistance to erosion, ablation, spalling, or galling.

Structural integrity: The ability to withstand a maximum-rated load while resisting fracture, resisting fatigue, and producing a minimal amount of flexing or deflection, to provide a maximum service life.