Steel glossary
Plain-language definitions of the heat-treatment, property, testing and corrosion terms used across this site — in the grades, guides and datasheets.
Annealing
Heating steel to a suitable temperature, holding, then cooling slowly to soften it, refine the structure, reli…
Austenite
The face-centred cubic phase of iron, stable at high temperature in all steels and at room temperature in aust…
Bainite
A fine ferrite–carbide structure formed at temperatures between pearlite and martensite ranges, giving a usefu…
Carbon equivalent (CEV)
A single number combining C, Mn, Cr, Mo, V, Ni and Cu by the IIW formula CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu…
Carburizing
Diffusing carbon into the surface of a low-carbon steel at 880–950 °C, then quenching, to produce a hard wear-…
Case hardening
Any process that hardens only the surface layer of a part while the core stays tough — carburizing, nitriding,…
Charpy impact test
A notched specimen is broken by a swinging pendulum and the absorbed energy (J) is recorded. It measures tough…
Cold drawn
Bar or tube pulled through a die at room temperature after hot rolling, giving tighter tolerances, a bright su…
Decarburization
Loss of carbon from the surface during heating in an oxidising atmosphere, leaving a soft skin that lowers fat…
Elongation (A)
The permanent extension of a tensile specimen at fracture, expressed as a percentage of the original gauge len…
ESR (electroslag remelting)
A secondary remelting process in which a consumable electrode is remelted through a slag bath, removing inclus…
Ferrite
The body-centred cubic, low-carbon phase of iron — soft, ductile and magnetic. It is the main phase in mild st…
Grain size
The average size of the crystals in steel, graded on the ASTM E112 scale (higher number = finer grain). Fine g…
Hardenability
The ability of a steel to harden in depth under quenching, governed mainly by alloying (Mn, Cr, Mo, B), not by…
Hardness
Resistance of a surface to indentation, measured as Rockwell (HRC/HRB), Brinell (HB) or Vickers (HV). Hardness…
Hot rolled
Steel shaped by rolling above the recrystallisation temperature (roughly above 900 °C). It has a scaled surfac…
Jominy end-quench test
A standard bar is austenitised and spray-quenched at one end; hardness is then measured along its length. The …
Machinability
How easily a steel can be cut — tool life, surface finish and chip control. Sulphur and lead additions create …
Martensite
The hard, needle-like phase formed when austenite is cooled fast enough to trap carbon in a distorted lattice.…
Mill test certificate (MTC)
The mill's document reporting the actual chemical composition and test results of a heat or lot. An EN 10204 3…
Nitriding
Diffusing nitrogen into the steel surface at 500–570 °C to form hard nitrides, without quenching and with mini…
Non-metallic inclusion
Oxide, sulphide or silicate particles trapped in steel during solidification. Cleanliness — rated by standards…
Normalizing
Heating steel about 30–50 °C above the upper critical temperature and cooling in air. It refines grain size, h…
Passivation
The formation (or restoration, after pickling or citric/nitric treatment) of the thin chromium-oxide film that…
Pcm
The Ito–Bessyo cracking parameter Pcm = C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B, designed for mo…
Pearlite
A lamellar mixture of ferrite and cementite formed on slow cooling of austenite. Its fineness controls the bal…
Pickling
Removing scale and rust by immersion in acid (hydrochloric or sulphuric for carbon steel, nitric–hydrofluoric …
Pitting corrosion
Localised corrosion that drills small deep holes, typically where chlorides break down the passive film of sta…
PREN (pitting resistance equivalent number)
An index of a stainless steel's resistance to pitting corrosion: PREN = %Cr + 3.3 × %Mo + 16 × %N (30 × %N in …
Quenching
Rapid cooling of steel from the austenitising temperature, usually in water, oil or polymer, to form martensit…
Seamless pipe
Pipe made by piercing or extruding a solid billet, with no weld seam. Preferred for high-pressure, high-temper…
Spheroidizing
Long holding at or just below Ac1 so that cementite forms spheres instead of lamellae. It gives the softest, m…
Stress relieving
Heating to 550–650 °C (below the transformation range), holding and cooling slowly, to remove residual stresse…
Tempering
Reheating quenched steel to a temperature below Ac1 (typically 150–650 °C) and cooling, to trade a little hard…
Tensile strength (Rm)
The maximum stress a material sustains in a tensile test before fracture, in MPa. Together with yield strength…
Through hardening
Hardening a part so that the required hardness is achieved through the whole section, not just at the surface …
Weldability
How readily a steel can be welded into a sound joint, governed mainly by carbon equivalent, thickness, hydroge…
Yield strength (Rp0.2)
The stress at which plastic deformation begins. For steels without a clear yield point it is quoted as Rp0.2 —…