Iron vs. Stainless Steel 303

Compare Iron vs. Stainless Steel 303 strength, stiffness, weight and thermal properties.

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IronWrought

Mechanical
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Yield strength	186MPasourcetypical (0.2% YS), hot rolled + SRA/recrystallization anneal	275MPasourceOutokumpu typical (product P = hot rolled plate, transverse)
Ultimate tensile strength	290MPasourcetypical, SRA/recrystallization anneal	585MPasourceOutokumpu typical
Elongation at break	38%sourcetypical, gauge 4D0	35%sourceOutokumpu typical, A5
Young's modulus (stiffness)	207GPasourcetypical, after SRA/recrystallization anneal	200GPasourceat RT (Table 12)
Density	7,860kg/m³sourcetypical	7,900kg/m³sourceat RT
Strength to weight	23.7kN·m/kg	34.8kN·m/kg47% higher
Stiffness to weight	26.3MN·m/kg4% higher	25.3MN·m/kg
Poisson's ratio	0.282sourceNIST critically evaluated best value (polycrystalline iron)	0.3sourcedesign value (structural stainless steels)
Shear modulus	80.7GPa5% stiffer in shear	76.9GPa
Bulk modulus	158GPa	167GPa
Speed of sound	5,132m/s	5,032m/s
Thermal
Thermal conductivity	73.2W/m·Ksourcetypical at 20 °C	15W/m·Ksourceat RT
Thermal expansion	13.7µm/m·Ksourcemean, 20-399 °C	16µm/m·Ksourcemean, 20–100 °C
100 mm part over a 50 °C swing	68.5µm growth17% less	80µm growth
Specific heat	450J/kg·Ksourcetypical	500J/kg·Ksourceat RT
Heats up and cools (diffusivity)	20.7mm²/s5.45x faster	3.8mm²/s
Thermal shock resistance	3,447W/m3.82x more resistant	902W/m
Melting point	1,532°Csourcetypical	not sourced
Max service temperature	not sourced	871°Csourcecontinuous, scaling limit
Values for	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.	1.4305 / UNS S30300, Outokumpu typical values (hot rolled, solution annealed) from 'Steel Grades, Properties and Global Standards'; max service from Carpenter CarTech 303 datasheet

Every value links to the document that states it. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.

Questions

Is Iron stronger than Stainless Steel 303?

Stainless Steel 303 is stronger: its yield strength is 275 MPa against 186 MPa for Iron (48%).

Which is lighter, Iron or Stainless Steel 303?

Iron is lighter: 7,860 kg/m³ against 7,900 kg/m³ for Stainless Steel 303.

Which is stiffer, Iron or Stainless Steel 303?

Iron is stiffer: Young's modulus 207 GPa against 200 GPa for Stainless Steel 303, so the same part in Iron deflects less under the same load.

Which is lighter for the same job, Iron or Stainless Steel 303?

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 303 is lighter for a strong rod or tie, strong beam, strong panel or plate.

Part that must be	Iron	Stainless Steel 303
Stiff rod or tie (tension)	lighter	4% heavier
Stiff beam (bending)	lighter	2% heavier
Stiff panel or plate	lighter	2% heavier
Strong rod or tie	47% heavier	lighter
Strong beam	29% heavier	lighter
Strong panel or plate	21% 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 conducts heat better, Iron or Stainless Steel 303?

Iron conducts heat better: 73.2 W/m·K against 15 W/m·K for Stainless Steel 303.

Which expands less with temperature?

Iron expands less: 13.7 µm/m·K against 16 µm/m·K for Stainless Steel 303.

Among 72 materials

Stiffness against density

Strength against density