Iron vs. Stainless Steel 304

Compare Iron vs. Stainless Steel 304 strength, stiffness, weight and thermal properties.

IronWrought

Mechanical	Iron	Stainless Steel 304
Yield strength	186MPa1	241MPa230% stronger
Ultimate tensile strength	290MPa1	586MPa22.02x stronger
Elongation at break	38%1	55%245% more ductile
Young's modulus (stiffness)	207GPa1	193GPa2
Density	7,860kg/m³1	8,030kg/m³2
Strength to weight	23.7kN·m/kg	30kN·m/kg27% higher
Stiffness to weight	26.3MN·m/kg10% higher	24MN·m/kg
Poisson's ratio	0.2823	design value0.34
Shear modulus	80.7GPa9% stiffer in shear	74.2GPa
Bulk modulus	158GPa	161GPa2% higher
Speed of sound	5,132m/s5% faster	4,903m/s

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Iron	Stainless Steel 304
Thermal conductivity	73.2W/m·K14.52x more heat through a fin	at 100 °C16.2W/m·K2
Thermal expansion	mean13.7µm/m·K123% less	mean16.9µm/m·K2
100 mm part over a 50 °C swing	68.5µm growth23% less	84.5µm growth
Specific heat	450J/kg·K1	mean500J/kg·K2
Heats up and cools (diffusivity)	20.7mm²/s5.13x faster	4.03mm²/s
Thermal shock resistance	3,447W/m4.11x more resistant	838W/m
Melting point	1,532°C1	melting range1,399–1,454°C2
Max service temperature	not sourced	continuous899°C2

Thermal conductivity against densityHigher and further left: spreads more heat for its weight

Thermal expansion against thermal conductivityLower and further right: warps less when heated

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Sources4 documents: Cleveland-Cliffs, National Institute of Standards and Technology, Steel Construction Institute

Iron: Cleveland-Cliffs / AK Steel ARMCO Pure Iron Product Data Bulletin (07/2022): Table 1 typical physical properties, Table 2 typical mechanical properties after SRA/recrystallization anneal.
Stainless Steel 304: Type 304, annealed flat-rolled (Cleveland-Cliffs 304/304L Product Data Bulletin, May 2021); Poisson's ratio from the Nickel Institute/SCI structural stainless design manual

1
ARMCO Pure Iron Product Data Bulletin (2022)Cleveland-Cliffsarchived copyIron · Yield strength: typical (0.2% YS), hot rolled + SRA/recrystallization annealIron · Ultimate tensile strength: typical, SRA/recrystallization annealIron · Elongation at break: typical, gauge 4D0Iron · Young's modulus (stiffness): typical, after SRA/recrystallization annealIron · Density: typicalIron · Thermal conductivity: typical at 20 °CIron · Thermal expansion: mean, 20-399 °CIron · Specific heat: typicalIron · Melting point: typical
2
304/304L Stainless Steel Product Data Bulletin (2021)Cleveland-CliffsStainless Steel 304 · Yield strength: typical, annealed, 70 °F (21 °C)Stainless Steel 304 · Ultimate tensile strength: typical, annealed, 70 °F (21 °C)Stainless Steel 304 · Elongation at break: typical, annealed, in 2 in. (50.8 mm)Stainless Steel 304 · Young's modulus (stiffness): typical, in tensionStainless Steel 304 · Density: typicalStainless Steel 304 · Thermal conductivity: at 100 °CStainless Steel 304 · Thermal expansion: mean, 0–100 °CStainless Steel 304 · Specific heat: mean, 0–100 °CStainless Steel 304 · Melting point: melting rangeStainless Steel 304 · Max service temperature: continuous, oxidation (scaling) limit in air
3
Elastic Properties of Metals and Alloys, I. Iron, Nickel, and Iron-Nickel Alloys, J. Phys. Chem. Ref. Data 2 (1973)National Institute of Standards and Technologyarchived copyIron · Poisson's ratio: NIST critically evaluated best value (polycrystalline iron)
4
Design Manual for Structural Stainless Steel, 4th Edition (P413)Steel Construction Institutearchived copyStainless Steel 304 · Poisson's ratio: design value (structural stainless steels)

Each number points to the document that states it, with the exact basis. Values without a number are computed from the sourced ones. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.

Questions

Mechanical

Is Iron stronger than Stainless Steel 304?

Stainless Steel 304 is stronger: its yield strength is 241 MPa against 186 MPa for Iron (30%).

Which is lighter, Iron or Stainless Steel 304?

Iron is lighter: 7,860 kg/m³ against 8,030 kg/m³ for Stainless Steel 304.

Which is stiffer, Iron or Stainless Steel 304?

Iron is stiffer: Young's modulus 207 GPa against 193 GPa for Stainless Steel 304, so the same part in Iron deflects less under the same load.

Which is lighter for the same job, Iron or Stainless Steel 304?

For the same stiffness or strength: Iron is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate; Stainless Steel 304 is lighter for a strong rod or tie, strong beam, strong panel or plate.

Part that must be	Iron	Stainless Steel 304
Stiff rod or tie (tension)	lighter	10% heavier
Stiff beam (bending)	lighter	6% heavier
Stiff panel or plate	lighter	5% heavier
Strong rod or tie	27% heavier	lighter
Strong beam	16% heavier	lighter
Strong panel or plate	11% heavier	lighter

For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).

Which is more ductile, Iron or Stainless Steel 304?

Stainless Steel 304 stretches further before it breaks: 55% elongation at break against 38% for Iron.

Thermal

Which conducts heat better, Iron or Stainless Steel 304?

Iron conducts heat better: 73.2 W/m·K against 16.2 W/m·K for Stainless Steel 304.

Which expands less with temperature?

Iron expands less: 13.7 µm/m·K against 16.9 µm/m·K for Stainless Steel 304.