Ferrous vs. non-ferrous
Ferrous alloys (iron-based — steel, cast iron) dominate structural and high-load applications on cost and stiffness; non-ferrous alloys (aluminum, titanium, copper, zinc, magnesium) trade some strength/stiffness for lower density, better corrosion resistance, or specific functional properties (conductivity, non-magnetic, biocompatibility).
Values are typical/nominal figures compiled from standard references (ASM Handbook, MatWeb, mill/resin datasheets, ASTM/ISO material standards) at room temperature unless noted. Real material batches vary with heat/lot, processing history, and orientation (especially for polymers and composites) — always verify against a certified mill test report or datasheet for critical/safety applications.
Carbon & alloy steel, cast iron
The structural workhorse family. Carbon content and alloying drive the strength/ductility/hardenability trade-off; cast irons trade ductility for damping and casting economy.
| Grade | Condition | UTS (MPa) | Yield (MPa) | Elong. (%) | Hardness | Modulus (GPa) |
|---|---|---|---|---|---|---|
| 1018 (low-C mild steel) | Hot rolled | 440 | 370 | 15 | 126 HB | 205 |
| 1045 (medium-C steel) | Normalized | 625 | 375 | 16 | 179 HB | 205 |
| A36 structural | As rolled | 400–550 | 250 | 20 | 150 HB | 200 |
| 4140 (Cr-Mo alloy) | Q&T (28 HRC) | 1020 | 655 | 17 | 285 HB | 205 |
| 4340 (Ni-Cr-Mo alloy) | Q&T (350 HB) | 1280 | 1170 | 12 | 350 HB | 205 |
| O1 tool steel | Hardened 58 HRC | ~1900 | — | <2 | 58 HRC | 207 |
| Gray cast iron (Class 30) | As cast | 210 | —*no yield pt. | <1 | 200 HB | 100–145 |
| Ductile iron 65-45-12 | As cast | 450 | 310 | 12 | 170 HB | 168 |
| Grade | Density (g/cm³) | Melt Pt (°C) | Machinability | Weldability | Relative Cost | Typical Use |
|---|---|---|---|---|---|---|
| 1018 mild steel | 7.87 | ~1520 | Good | Excellent | $ | Brackets, shafts, general fabrication |
| 1045 medium-C | 7.85 | ~1480 | Moderate | Fair — preheat | $ | Gears, axles, medium-strength shafts |
| 4140 alloy steel | 7.85 | ~1420 | Moderate | Fair — preheat/PWHT | $$ | High-strength shafts, tooling, fasteners |
| 4340 alloy steel | 7.85 | ~1425 | Harder | Difficult | $$ | Aerospace landing gear, high-stress shafts |
| Gray cast iron | 7.15 | ~1200 | Excellent | Poor | $ | Machine bases, engine blocks — damping/wear |
| Ductile iron | 7.10 | ~1150 | Moderate | Poor | $ | Housings, crankshafts — needs ductility |
Stainless steel — austenitic, martensitic, PH, duplex
Corrosion resistance comes from a passive chromium-oxide layer (min. ~10.5% Cr). The four families trade off corrosion resistance, strength, hardenability and magnetic response very differently — picking the wrong family is one of the most common material-selection mistakes.
Non-magnetic, not hardenable by heat treatment (work-hardens only), best corrosion resistance and weldability of the four families. Default choice unless you need higher strength or magnetic response is a problem.
Magnetic, hardenable by quench & temper like carbon steel. Good wear resistance and moderate corrosion resistance. Used for cutlery, valve parts, shafts needing hardness.
Machine in the solution-annealed (soft) state, then age-harden (H900–H1150) for high strength with good corrosion resistance — a common aerospace/medical choice.
Mixed austenite/ferrite microstructure — roughly double the yield strength of 304/316 with excellent chloride stress-corrosion cracking resistance. Offshore/marine/chemical processing.
| Grade | Family | Condition | UTS (MPa) | Yield (MPa) | Elong. (%) | Hardness | Magnetic? |
|---|---|---|---|---|---|---|---|
| 303 | Austenitic | Annealed | 620 | 240 | 50 | 160 HB | No |
| 304 / 304L | Austenitic | Annealed | 580 | 240 | 55 | 150 HB | No (slight after CW) |
| 316 / 316L | Austenitic | Annealed | 580 | 260 | 50 | 150 HB | No (slight after CW) |
| 410 | Martensitic | Hardened & tempered | 700–1200 | 500–1000 | 15–22 | 92–235 HB | Yes |
| 420 | Martensitic | Hardened (50 HRC) | 1500 | 1350 | 8 | 50 HRC | Yes |
| 17-4PH | Precipitation-hardening | H900 | 1310 | 1170 | 10 | 40 HRC | Yes |
| 2205 Duplex | Duplex | Annealed | 760 | 485 | 25 | 293 HB | Yes (mild) |
| Grade | Density (g/cm³) | Thermal Cond. (W/m·K) | Max Service Temp (°C) | Chloride/Pitting Res. | Machinability | Relative Cost |
|---|---|---|---|---|---|---|
| 303 | 8.00 | 16.2 | 870 | Good | Best of SS (free-machining) | $$ |
| 304 / 304L | 8.00 | 16.2 | 870 | Good | Fair — gummy, work-hardens | $$ |
| 316 / 316L | 8.00 | 16.3 | 870 | Very good (Mo-alloyed) | Fair | $$$ |
| 410 | 7.70 | 24.9 | 650 | Moderate | Fair (soft/annealed) | $$ |
| 420 | 7.75 | 24.9 | 650 | Moderate | Poor (hardened) | $$ |
| 17-4PH | 7.80 | 17.9 | 315 (retains strength) | Good | Fair (machine before aging) | $$$ |
| 2205 Duplex | 7.80 | 19 | 300 | Excellent | Difficult — high work-hardening | $$$$ |
Specifying 304 for a chloride-exposed environment (pool chemicals, de-icing salt, coastal air, brackish water) — 304 is prone to pitting/crevice corrosion in chlorides above roughly 200 ppm. 316/316L (Mo-alloyed) or duplex 2205 is the correct default for any chloride exposure.
Aluminum alloys
~1/3 the density of steel with good corrosion resistance and machinability. The 4-digit series designates the primary alloying element (1xxx pure, 2xxx Cu, 5xxx Mg, 6xxx Mg+Si, 7xxx Zn); temper designation (-O, -T4, -T6, -H32...) matters as much as the base alloy.
| Alloy | Temper | UTS (MPa) | Yield (MPa) | Elong. (%) | Hardness (HB) | Modulus (GPa) |
|---|---|---|---|---|---|---|
| 1100 | O (annealed) | 90 | 34 | 35 | 23 | 69 |
| 5052 | H32 | 230 | 195 | 12 | 60 | 70 |
| 6061 | T6 | 310 | 276 | 12 | 95 | 69 |
| 2024 | T3 | 485 | 345 | 18 | 120 | 73 |
| 7075 | T6 | 572 | 503 | 11 | 150 | 72 |
| A356 (cast) | T6 | 262 | 186 | 6 | 80 | 72 |
| Alloy | Density (g/cm³) | Thermal Cond. (W/m·K) | Corrosion Res. | Weldability | Machinability | Typical Use |
|---|---|---|---|---|---|---|
| 1100 | 2.71 | 222 | Excellent | Excellent | Fair — gummy | Chemical tanks, heat exchangers, foil |
| 5052 | 2.68 | 138 | Excellent (incl. marine) | Excellent | Fair | Sheet metal enclosures, marine fittings |
| 6061 | 2.70 | 167 | Very good | Good | Good | General structural — the default 6xxx |
| 2024 | 2.78 | 121 | Poor — needs cladding | Poor (not fusion-weldable) | Good | Aircraft skin/structure — fatigue-critical |
| 7075 | 2.81 | 130 | Moderate — SCC risk | Poor (not fusion-weldable) | Good | Highest-strength Al — aerospace, tooling plate |
| A356 (cast) | 2.68 | 151 | Good | Fair | Good | Sand/permanent-mold/investment castings |
2xxx and 7xxx series are the high-strength "aircraft" alloys but are essentially not fusion-weldable (hot cracking) — mechanical fastening or friction-stir welding instead. 5xxx and 6xxx weld well with standard GMAW/GTAW; 6xxx loses temper strength in the heat-affected zone unless re-aged after welding.
Titanium alloys
Best strength-to-weight ratio of any structural metal, outstanding corrosion resistance (self-healing oxide film), biocompatible — at a machining-cost and material-cost premium several times that of stainless steel.
| Grade | Type | UTS (MPa) | Yield (MPa) | Elong. (%) | Density (g/cm³) | Modulus (GPa) | Max Service Temp (°C) |
|---|---|---|---|---|---|---|---|
| Grade 2 (CP-Ti) | Commercially pure | 345 | 275 | 20 | 4.51 | 103 | 430 |
| Grade 5 (Ti-6Al-4V) | Alpha-beta | 950 | 880 | 14 | 4.43 | 114 | 400 |
| Grade 23 (Ti-6Al-4V ELI) | Alpha-beta, medical | 860 | 795 | 15 | 4.43 | 114 | 400 |
Raw material cost runs ~5–8× that of 316 stainless per kilogram — despite titanium being roughly half the density of steel, so less material is needed by weight for the same volume. Machinability is also poor — low thermal conductivity concentrates heat at the cutting edge, the material work-hardens readily, and it requires low speeds/high feeds with sharp, rigid tooling. Expect 3–5× the machining time of aluminum for equivalent geometry.
Aerospace structure, medical implants (biocompatible, MRI-safe), marine/chemical components needing both strength and corrosion resistance, and any application where the weight saved is worth far more than the material premium.
Copper, brass, zinc & magnesium
Specialty metals chosen for a specific functional property rather than general structural use — conductivity, castability, or weight.
| Material | UTS (MPa) | Density (g/cm³) | Elec. Cond. (%IACS) | Primary Reason to Specify |
|---|---|---|---|---|
| Copper C110 (ETP) | 220–345 | 8.94 | 101 | Best commodity electrical/thermal conductivity — bus bars, heat sinks, windings |
| Brass C360 (free-cutting) | 340 | 8.50 | 26 | Excellent machinability, decorative — fittings, valves, fasteners |
| Bronze C932 (bearing) | 240 | 8.64 | 14 | Low-friction, self-lubricating — bushings, worm gears |
| Zamak 3 (zinc die-cast) | 283 | 6.60 | 27 | Cheap, high-precision die casting for small hardware |
| Magnesium AZ31B | 260 | 1.77 | 9.7 | Lightest structural metal — electronics housings, aerospace brackets |
Thermoplastics vs. thermosets
Thermoplastics soften/re-melt on heating (recyclable, weldable, generally tougher) — semi-crystalline grades (PP, POM, PA, PEEK) resist chemicals and fatigue better; amorphous grades (ABS, PC, PMMA) are more dimensionally stable and often transparent. Thermosets cross-link irreversibly on cure — better creep/temperature resistance and dimensional stability but brittle and non-recyclable.
Commodity & engineering thermoplastics — incl. ABS & PC
| Material | Tensile Str. (MPa) | Elong. (%) | Flex. Modulus (GPa) | HDT @0.45MPa (°C) | Notched Izod (J/m) | Density (g/cm³) |
|---|---|---|---|---|---|---|
| PP (polypropylene) | 30–38 | 150–300 | 1.2–1.7 | 100 | 30–60 | 0.90 |
| HDPE | 22–31 | 400–700 | 1.0–1.5 | 75 | no break | 0.95 |
| PVC (rigid) | 45–52 | 40–80 | 2.4–3.0 | 70 | 50–90 | 1.40 |
| ABS | 40–45 | 10–50 | 2.1–2.4 | 96–102 | 200–400 | 1.05 |
| PC (polycarbonate) | 60–70 | 80–150 | 2.3–2.4 | 135–140 | 600–850 | 1.20 |
| PC/ABS blend | 50–55 | 60–100 | 2.2 | 110–125 | 400–550 | 1.13 |
| PA6 (Nylon 6) | 75–85 (dry) | 50–150 | 2.6–3.0 | 75–90 | 50–100 | 1.13 |
| PA66 (Nylon 6/6) | 80–90 (dry) | 30–60 | 2.8–3.3 | 75–100 | 50–110 | 1.14 |
| POM (Acetal/Delrin) | 65–70 | 25–75 | 2.6–3.1 | 110–160 | 60–120 | 1.41 |
| PET | 55–60 | 50–300 | 2.8–3.1 | 65–80 | 30–40 | 1.37 |
| PMMA (acrylic) | 65–75 | 2–10 | 2.9–3.3 | 85–100 | 16–25 | 1.18 |
| Material | UV/Weathering | Chemical Res. | Optical Clarity | Relative Cost | Typical Use |
|---|---|---|---|---|---|
| PP | Poor (chalks) | Excellent (acids/bases) | Opaque/translucent | $ | Living hinges, chemical containers, packaging |
| HDPE | Fair | Excellent | Opaque | $ | Tanks, piping, cutting boards |
| ABS | Poor — UV yellows/embrittles | Fair — attacked by ketones/esters | Opaque (paintable) | $$ | Enclosures, automotive trim, consumer products, 3D printing |
| PC (polycarbonate) | Fair — needs UV coat outdoors | Poor — stress-cracks with solvents/alkalis | Excellent (glass-clear) | $$$ | Safety glazing, lenses, machine guards, electronics |
| PA6/PA66 (Nylon) | Fair | Good (fuels/oils) | Opaque | $$ | Gears, bushings, fasteners — absorbs moisture, swells |
| POM (Acetal) | Fair | Good (fuels/solvents) | Opaque | $$ | Precision gears, snap-fits, low-friction parts |
| PMMA (acrylic) | Excellent | Poor — solvent-attacked | Excellent (best optical) | $$ | Outdoor glazing, signage, lenses (non-impact) |
ABS is picked by default for enclosures but is a poor choice outdoors (UV embrittlement within months unless stabilized/painted) and has mediocre impact strength at low temperature. If the part needs UV exposure, impact strength, or higher heat resistance, PC (or PC/ABS blend for a machinability/cost middle ground) is usually the better call — at roughly 1.5–2× the material cost.
High-performance thermoplastics — PEEK & PEI
The step above engineering plastics — continuous service well above 150°C, chemical resistance rivaling some metals, and inherent flame resistance (PEI/Ultem) — at 10–30× the cost of ABS.
| Material | Tensile Str. (MPa) | Flex. Modulus (GPa) | HDT @1.8MPa (°C) | Cont. Use Temp (°C) | UL94 Flame | Density (g/cm³) | Relative Cost |
|---|---|---|---|---|---|---|---|
| PEEK | 90–100 | 3.7–4.1 | 152–160 | 250 | V-0 | 1.30 | $$$$$ |
| PEEK (30% CF) | 195–215 | 9–10 | 315 | 250 | V-0 | 1.44 | $$$$$ |
| PEI (Ultem 1000) | 100–105 | 3.2–3.4 | 200 | 170 | V-0 | 1.27 | $$$$ |
| PPS (Ryton) | 65–75 | 3.8–4.5 | 260 | 220 | V-0 | 1.35 | $$$$ |
| PSU (Udel) | 70–75 | 2.5–2.7 | 174 | 160 | HB–V-0 | 1.24 | $$$$ |
| PEI 30% Glass-Filled | 145–155 | 8.5–9.5 | 210 | 170 | V-0 | 1.51 | $$$$ |
| PPS 40% Glass-Filled | 180–200 | 13–15 | 265 | 220 | V-0 | 1.66 | $$$$ |
| PSU 20% Glass-Filled | 105–115 | 5.5–6.5 | 178 | 160 | HB–V-0 | 1.40 | $$$$ |
Semi-crystalline, exceptional fatigue/wear resistance and chemical resistance (including steam sterilization). Standard in medical implants, semiconductor process components, and aerospace parts replacing metal for weight.
Amorphous, naturally flame-retardant without additives, transparent-amber, excellent dimensional stability — the go-to for aircraft interior components and medical sterilization trays where inherent flame rating matters.
Both require melt temperatures of 350–420°C and heated molds (PEEK ~150–200°C mold temp for full crystallinity) — standard injection molding equipment often can't reach these without upgrades, which is part of why per-part cost is high even before resin price. See the Process Tolerances reference for achievable tolerances by process.
Thermosets
| Material | Tensile Str. (MPa) | Max Service Temp (°C) | Elec. Insulation | Typical Use |
|---|---|---|---|---|
| Epoxy (cast/potting) | 55–90 | 120–180 | Excellent | Encapsulation, tooling, composite matrix resin |
| Phenolic | 35–60 | 150–200 | Excellent | Electrical components, brake pads, laminates |
| Unsaturated polyester | 40–90 | 120 | Good | GFRP composite matrix, low-cost tooling |
| Cast polyurethane | 20–55 | 80–100 | Good | Wheels, gaskets, flexible/rigid parts, prototyping |
| Silicone (RTV) | 2.5–10 | 200–300 | Excellent | Seals, gaskets, molds — extreme temp/flex range |
Technical & engineering ceramics
Hardness, wear resistance, and temperature capability far beyond metals or polymers — at the cost of brittleness (near-zero ductility) and difficult, diamond-tooling-dependent machining. Nearly always finish-machined by grinding rather than cut to final shape by conventional metalworking.
| Material | Flexural Str. (MPa) | Compressive Str. (MPa) | Hardness (HV) | Max Service Temp (°C) | Density (g/cm³) | Elec. Property |
|---|---|---|---|---|---|---|
| Alumina (Al₂O₃, 96–99.5%) | 300–400 | 2000–2600 | 1400–1650 | 1700 | 3.7–3.9 | Insulator |
| Zirconia (ZrO₂, YSZ) | 800–1200 | 2000 | 1200–1300 | 1000–1200 | 6.0 | Insulator |
| Silicon Carbide (SiC) | 350–550 | 2000–3900 | 2400–2800 | 1600 | 3.1 | Semiconductor |
| Silicon Nitride (Si₃N₄) | 700–1000 | 3000+ | 1400–1800 | 1200 | 3.2 | Insulator |
| Aluminum Nitride (AlN) | 300–400 | 2000 | 1100–1200 | 1000 | 3.3 | Insulator, high thermal cond. |
| Macor (machinable glass-ceramic) | 94 | 345 | 250 | 800 | 2.52 | Insulator |
Every ceramic above except Macor must be machined green (unfired) or diamond-ground after firing — conventional cutting tools don't work. Macor's mica-glass structure machines with standard carbide tooling on ordinary equipment, at a large strength/temperature penalty versus fired technical ceramics — useful when a one-off precision insulating part is needed without diamond-grinding lead time and cost.
Fiber-reinforced composites
Properties are strongly direction-dependent (anisotropic) — the numbers below are representative for the fiber direction stated; off-axis and interlaminar (through-thickness) properties are much lower. Short-fiber-filled thermoplastics behave closer to isotropic but with reduced properties versus continuous-fiber laminates.
| Material | Tensile Str. (MPa) | Tensile Modulus (GPa) | Density (g/cm³) | Max Service Temp (°C) | Notes |
|---|---|---|---|---|---|
| CFRP, unidirectional (0°) | 1500–2500 | 135–170 | 1.55–1.60 | 120–180 (epoxy matrix) | Best strength/stiffness-to-weight; fiber-direction dependent |
| CFRP, woven (quasi-isotropic) | 550–700 | 55–70 | 1.55–1.60 | 120–180 | More balanced in-plane properties, easier layup |
| GFRP (E-glass/epoxy) | 700–1200 (UD) | 35–45 | 1.85–2.0 | 120–150 | Lower cost, non-conductive, good impact tolerance |
| Aramid/epoxy (Kevlar) | 1200–1400 | 70–80 | 1.35–1.40 | 150 | Best impact/ballistic energy absorption, poor compression |
| Glass-filled Nylon (30% GF) | 140–180 | 8–10 | 1.35 | 150–170 | Injection-moldable, near-isotropic, common metal-replacement |
| Carbon-filled PEEK (30% CF) | 195–215 | 9–10 | 1.44 | 250 | High-performance moldable composite — see PEEK section |
| Aluminum/SiC Metal-Matrix Composite | 330–370 | 95–105 | 2.90 | 250 | Al reinforced with SiC particulate — stiffer/harder than 6061, abrasive to machine on standard tooling |
| C/SiC Ceramic-Matrix Composite | 280–320 | 85–95 | 2.10 | 1400 | Carbon-fiber-reinforced SiC — retains strength at extreme temperature where CFRP/polymers cannot; aerospace, brake discs |
Continuous-fiber laminates (CFRP/GFRP prepreg or wet layup) give the highest performance but need mold tooling, layup labor/autoclave, and design expertise in ply orientation — best for low-to-mid volume, high-value parts. Short-fiber-filled thermoplastics (glass/carbon-filled nylon, PEEK, etc.) mold like any other plastic on standard injection equipment — far better for volume production, at roughly a third of the stiffness of continuous-fiber laminates.
Cross-family quick comparison
A single-table gut check across representative materials from every family, for early-stage material selection before diving into the full property tables above.
| Material | Density (g/cm³) | Specific Strength (kN·m/kg) | Max Service Temp (°C) | Corrosion/Chem. Res. | Relative Cost | Machinability/Moldability |
|---|---|---|---|---|---|---|
| Mild steel (1018) | 7.87 | 56 | ~500 | Poor (rusts) | $ | Good |
| Stainless 316L | 8.00 | 73 | 870 | Very good | $$$ | Fair |
| Aluminum 6061-T6 | 2.70 | 115 | ~150 (strength drops) | Very good | $$ | Good |
| Titanium Ti-6Al-4V | 4.43 | 214 | 400 | Excellent | $$$$$ | Poor |
| ABS | 1.05 | ~40 | ~80 | Fair | $$ | Excellent (molding) |
| PEEK | 1.30 | ~74 | 250 | Excellent | $$$$$ | Fair (needs hot tooling) |
| Alumina ceramic | 3.85 | ~90 (flexural) | 1700 | Excellent | $$$ | Diamond-grind only |
| CFRP unidirectional | 1.58 | 1265 | 150 | Excellent | $$$$ | Tooling/layup dependent |
Specific strength (strength ÷ density) is the fair comparison when weight matters — it's why titanium and CFRP dominate aerospace despite a much higher $/kg than steel: less material is needed to carry the same load.