A reference library of the most important elements in metallurgical engineering — covering their atomic properties, metallurgical roles, alloying effects, and key applications. This resource is intended as a quick reference for engineers, students, and materials professionals selecting alloys or studying the effects of composition on microstructure and properties.

Jump to element:
Al · B · C · Cr · Cu · Fe · Mn · Mo · Ni · Nb · N · P · Si · S · Ti · W · V · Zn

Iron (Fe) — The Foundation Metal

Atomic Number 26 Crystal Structure BCC (α below 912°C), FCC (γ 912–1394°C)
Melting Point 1538°C Density 7.87 g/cm³
Young’s Modulus ~211 GPa Magnetic Ferromagnetic (below Curie point 770°C)

Iron is the basis of all steels and cast irons — the most widely used engineering metals. Pure iron is soft and ductile; its properties are dramatically altered by alloying, particularly with carbon. The Fe-C phase diagram is the single most important reference in ferrous metallurgy, governing heat treatment, microstructure, and property design of all carbon and alloy steels.

Carbon (C) — The Master Alloying Element in Steel

Atomic Number 6 Role in Steel Interstitial solid solution + carbide former
Effect on Strength Strong increase in YS and UTS Effect on Weldability Reduces weldability; raises CE
Effect on Toughness Reduces toughness above ~0.3 wt% Effect on Hardness Largest single influence on as-quenched hardness

Carbon is the most powerful and cost-effective strengthening element in steel. It strengthens by interstitial solid solution, precipitation of carbides, and dramatic increase in hardenability. However, increasing carbon reduces weldability, toughness, and ductility. Modern structural steels minimise carbon content and use microalloying (Nb, V, Ti) to achieve strength with good weldability.

Chromium (Cr) — Corrosion Resistance and Hardenability

Atomic Number 24 Density 7.19 g/cm³
Key Role Passivation layer (Cr₂O₃), carbide former, hardenability Minimum for Stainless ≥10.5 wt% Cr

Chromium is the essential element in stainless steels. Above ~10.5 wt%, chromium forms a stable, self-healing passive oxide layer (Cr₂O₃) that protects the underlying metal from corrosion. In alloy steels, chromium increases hardenability, elevated temperature strength, and oxidation resistance. As a carbide former, Cr carbides increase wear resistance but can cause sensitisation in stainless steels if precipitated at grain boundaries.

Nickel (Ni) — Toughness, Corrosion Resistance, and Austenite Stabiliser

Atomic Number 28 Crystal Structure FCC
Density 8.91 g/cm³ Melting Point 1455°C

Nickel is a potent austenite stabiliser in stainless steels, expanding the austenite phase field and enabling the austenitic microstructure at room temperature (e.g., 304, 316 stainless). In alloy steels, nickel significantly improves low-temperature toughness — essential for cryogenic pressure vessels, LNG tanks, and arctic pipelines. Nickel also improves corrosion resistance, solid solution strengthens, and increases hardenability without forming carbides.

Molybdenum (Mo) — Creep Resistance and Pitting Resistance

Atomic Number 42 Density 10.28 g/cm³
Melting Point 2623°C Key Effect Pitting Resistance Equivalent (PRE), creep resistance, hardenability

Molybdenum substantially increases pitting and crevice corrosion resistance in stainless steels — quantified in the Pitting Resistance Equivalent (PRE = %Cr + 3.3×%Mo + 16×%N). 316 stainless (2–3% Mo) offers significantly better pitting resistance than 304 in chloride environments. In Cr-Mo alloy steels, molybdenum improves elevated temperature strength and creep resistance for boiler and pressure vessel applications. It also increases hardenability and reduces temper embrittlement.

Manganese (Mn) — Deoxidiser, Sulphide Former, and Solid Solution Strengthener

Atomic Number 25 Density 7.47 g/cm³
Key Role Deoxidiser, MnS former (neutralises sulphur), solid solution strengthener, increases hardenability Typical Range in Steel 0.3–1.8 wt%

Manganese is present in virtually all steels. Its primary beneficial roles are: deoxidation during steelmaking; combining with sulphur to form MnS inclusions (preventing brittle FeS grain boundary films); and solid solution strengthening. Manganese also increases hardenability and lowers the eutectoid temperature. In Hadfield steels (11–14% Mn), the high manganese content produces a fully austenitic, work-hardening, highly wear-resistant steel.

Silicon (Si) — Deoxidiser and Ferrite Stabiliser

Atomic Number 14 Typical Range in Steel 0.15–0.35 wt% (structural); up to 3–4% in electrical steels
Key Role Deoxidiser, solid solution strengthener, increases oxidation resistance, ferrite stabiliser

Silicon is a standard deoxidising element in steelmaking. It strengthens ferrite by solid solution and raises the elastic limit. In high-silicon electrical steels (transformer cores), silicon reduces eddy current losses by increasing electrical resistivity. Silicon also improves oxidation resistance at elevated temperatures. Higher silicon levels reduce toughness and weldability.

Aluminium (Al) — Deoxidiser, Grain Refiner, and Structural Metal

Atomic Number 13 Crystal Structure FCC
Density 2.70 g/cm³ Melting Point 660°C
Young’s Modulus ~69 GPa Typical Tensile Strength 70 MPa (pure) to 700+ MPa (7xxx alloys)

Aluminium is the world’s most widely used non-ferrous structural metal — prized for its low density, good corrosion resistance (passive Al₂O₃ layer), high strength-to-weight ratio (especially in age-hardened 2xxx, 6xxx, 7xxx alloys), and excellent electrical conductivity. In steel, aluminium is used as a deoxidiser and grain refiner (aluminium nitrides pin grain boundaries, producing fine grain size and improved toughness).

Vanadium (V) — Microalloying Element and Carbide/Nitride Former

Atomic Number 23 Typical Amount in HSLA Steel 0.02–0.15 wt%
Key Role Grain refinement, precipitation strengthening via V(C,N), increases hardenability

Vanadium is a key microalloying element in high-strength low-alloy (HSLA) steels. Small additions (0.02–0.10%) form fine vanadium carbonitrides V(C,N) that pin grain boundaries and precipitate during controlled rolling/cooling — simultaneously refining grain size and providing precipitation strengthening. Vanadium is also used in tool steels and high-speed steels for wear resistance.

Niobium / Columbium (Nb/Cb) — Grain Refiner and HSLA Strengthener

Atomic Number 41 Typical Amount in HSLA Steel 0.02–0.06 wt%
Key Role Grain refinement by NbC/NbN precipitation, retards recrystallisation during TMCP, precipitation strengthening

Niobium is the most potent grain-refining microalloying element. NbC and NbN precipitates dissolve during austenitising and re-precipitate during controlled hot rolling (TMCP — thermomechanical controlled processing), retarding austenite recrystallisation and producing very fine grain sizes. This simultaneously increases strength and toughness — the unique advantage of microalloying compared to other strengthening mechanisms. Used extensively in pipeline steels (API 5L X65–X100) and structural steels.

Titanium (Ti) — Lightweight Structural Metal and Microalloying Element

Atomic Number 22 Crystal Structure HCP (α below 882°C), BCC (β above 882°C)
Density 4.51 g/cm³ Melting Point 1668°C
Corrosion Resistance Excellent (TiO₂ passive layer) Key Application Aerospace, medical implants, chemical processing

Titanium is valued for its exceptional strength-to-weight ratio, excellent corrosion resistance (especially in seawater and acidic environments), and biocompatibility. Titanium alloys (notably Ti-6Al-4V — “Grade 5”) are used extensively in aerospace structures, gas turbine compressor blades, biomedical implants, and chemical processing equipment. In steels, titanium is used as a microalloying element and to stabilise stainless steels against sensitisation (Grade 321).

Tungsten (W) — Highest Melting Point Metal

Atomic Number 74 Melting Point 3422°C (highest of all metals)
Density 19.25 g/cm³ Key Application High speed steels, WC cutting tools, TIG welding electrodes, lamp filaments

Tungsten has the highest melting point of any metal and outstanding high-temperature strength. It forms extremely hard tungsten carbide (WC) — the basis of cemented carbide (hardmetal) cutting tools used for machining, drilling, and mining. In high-speed steels (HSS), tungsten maintains hardness at cutting temperatures. Tungsten is also used in TIG/GTAW welding as the non-consumable electrode material.

Boron (B) — Ultra-Low Addition, Maximum Hardenability Effect

Atomic Number 5 Typical Addition in Steel 0.0005–0.003 wt% (5–30 ppm)
Key Role Extreme hardenability increase at very low concentrations; only effective in fully deoxidised, nitrogen-free steel

Boron is the most potent hardenability element per unit weight in steel. As little as 0.001% (10 ppm) of boron can double or triple the hardenability of steel by segregating to austenite grain boundaries and retarding ferrite nucleation during cooling. Used in quench-and-temper structural steels, case-hardening grades, and ultra-high-strength steels (Usibor, 22MnB5 press-hardening steels). Effectiveness requires that all nitrogen be fixed (by Al or Ti) to prevent boron nitride formation.

Copper (Cu) — Atmospheric Corrosion Resistance and Precipitation Hardening

Atomic Number 29 Crystal Structure FCC
Density 8.96 g/cm³ Electrical Conductivity Second highest of all metals (after silver)

Copper improves atmospheric corrosion resistance of steels (weathering steels, e.g. Corten contain ~0.3–0.5% Cu). In precipitation-hardening stainless steels (17-4 PH, 15-5 PH), copper precipitates are the primary strengthening phase. Copper is the primary electrical and thermal conductor in engineering — used in power transmission, heat exchangers, and electronics. Copper alloys include brass (Cu-Zn), bronze (Cu-Sn), and cupronickel (Cu-Ni).

Zinc (Zn) — Galvanic Corrosion Protection

Atomic Number 30 Crystal Structure HCP
Density 7.13 g/cm³ Melting Point 420°C
Key Application Galvanising (hot-dip zinc coating for steel corrosion protection), brass alloys, die casting

Zinc is primarily used to protect steel from corrosion by galvanising — applying a zinc coating that acts as both a barrier and a sacrificial anode (zinc is anodic to steel in the galvanic series). Hot-dip galvanising, electrogalvanising, and zinc-rich primers are all widely used in structural steel, automotive, and infrastructure applications. Zinc is also the major alloying element in brass (Cu-Zn alloys, 5–45% Zn).

Nitrogen (N) — Austenite Stabiliser and Strengthener

Atomic Number 7 Role in Stainless Steel Austenite stabiliser, pitting resistance (PRE contribution ×16), precipitation strengthener
Role in Structural Steel Can cause strain ageing embrittlement; fixed by Al or Ti as nitrides for grain refinement

Nitrogen is a powerful austenite stabiliser — ~20× more effective than nickel per weight percent — used in duplex and super-austenitic stainless steels to stabilise austenite and increase pitting resistance (PRE formula includes 16×%N). High-nitrogen stainless steels (e.g., 254 SMO, SAF 2507) achieve excellent corrosion resistance in aggressive chloride environments. In carbon steels, free nitrogen causes strain-age embrittlement (blue brittleness) — harmful unless fixed as AlN or TiN.

Phosphorus (P) — Tramp Element (Generally Harmful)

Atomic Number 15 Typical Limit in Structural Steel ≤0.035 wt% (many specs ≤0.020%)
Key Effect Segregates to grain boundaries; causes temper embrittlement and cold shortness; increases strength but reduces toughness

Phosphorus is generally regarded as a harmful tramp element in steels. It segregates strongly to prior austenite grain boundaries, causing temper embrittlement (reducing Charpy toughness after tempering or PWHT in the 350–550°C range) and cold shortness (brittleness at room temperature). Very low phosphorus (<0.010%) is specified for high-toughness applications. A controlled exception: phosphorus (0.07–0.15%) improves the atmospheric corrosion resistance of weathering steels (e.g., Corten).

Sulphur (S) — Machinability vs. Toughness Trade-off

Atomic Number 16 Typical Limit in Structural Steel ≤0.035 wt% (high-toughness specs ≤0.005%)
Key Effect Forms MnS inclusions; high S improves machinability (free-machining steels); low S required for high toughness (especially transverse/through-thickness)

Sulphur combines with manganese to form MnS inclusions. These improve machinability (free-machining steels contain 0.1–0.35% S) but are highly detrimental to transverse and through-thickness toughness, ductility, and fatigue life — MnS inclusions act as crack initiation sites. For demanding structural, pressure vessel, and offshore applications, very low sulphur (<0.005%) is required, often combined with calcium treatment to modify inclusion morphology from elongated stringers to globular form.

This elements library covers the principal alloying and impurity elements relevant to ferrous and non-ferrous engineering metallurgy. Additional elements will be added in future updates.

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