Plastic PBT GF30 vs. Stainless Steel 17-4PH

Compare Plastic PBT GF30 vs. Stainless Steel 17-4PH strength, stiffness, weight and thermal properties.

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Plastic PBT GF30Bulk polymer (molded or machined)

Mechanical
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Yield strength	not given (tensile used)	1,275MPasourcetypical, transverse, sheet/strip
Ultimate tensile strength	140MPasourcestress at break, 23 °C	1,379MPasourcetypical, transverse, sheet/strip
Flexural strength	210MPasourcetypical, 23 °C	not sourced
Elongation at break	3%sourcestrain at break, 23 °C	9%sourcetypical, transverse, in 2 in. (50.8 mm)
Young's modulus (stiffness)	9.8GPasourcetypical, 23 °C	197GPasourceH 900
Density	1,530kg/m³sourcetypical	7,800kg/m³sourceH 900
Strength to weight	91.5kN·m/kg	163kN·m/kg1.79x higher
Stiffness to weight	6.41MN·m/kg	25.3MN·m/kg3.94x higher
Poisson's ratio	not sourced	0.272sourceH 900 (column)
Shear modulus	not sourced	77.4GPa
Bulk modulus	not sourced	144GPa
Speed of sound	2,531m/s	5,026m/s
Thermal
Thermal conductivity	0.27W/m·Ksourcetypical (DIN 52612-1)	17.9W/m·Ksourceat 149 °C (300 °F), H 900
Thermal expansion	25µm/m·Ksourcelongitudinal (flow), mean 23-55 °C	10.8µm/m·Ksourcemean, 21–93 °C (70–200 °F), H 900
100 mm part over a 50 °C swing	125µm growth	54µm growth2.31x less
Specific heat	1,050J/kg·Ksourcetypical, 23 °C	460J/kg·Ksourcemean, 0–100 °C, H 900
Heats up and cools (diffusivity)	0.168mm²/s	4.99mm²/s29.7x faster
Thermal shock resistance	not sourced	7,809W/m
Melting point	223°CsourceDSC (ISO 11357)	not sourced
Max service temperature	205°CsourceHDT 1.8 MPa	316°Csourcestrength-retention limit (not oxidation)
Values for	BASF Ultradur B 4300 G6 (PBT, 30% glass fibre), injection moulding grade; product information sheet 09/2026, typical values for uncoloured product at 23 °C.	Cleveland-Cliffs 17-4 PH, Condition H 900, sheet/strip, transverse (Product Data Bulletin, May 2021)

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 Plastic PBT GF30 stronger than Stainless Steel 17-4PH?

Stainless Steel 17-4PH is stronger: its yield strength is 1,275 MPa against tensile strength 140 MPa for Plastic PBT GF30 (9.11x).

Which is lighter, Plastic PBT GF30 or Stainless Steel 17-4PH?

Plastic PBT GF30 is lighter: 1,530 kg/m³ against 7,800 kg/m³ for Stainless Steel 17-4PH.

Which is stiffer, Plastic PBT GF30 or Stainless Steel 17-4PH?

Stainless Steel 17-4PH is stiffer: Young's modulus 197 GPa against 9.8 GPa for Plastic PBT GF30, so the same part in Stainless Steel 17-4PH deflects less under the same load.

Which is lighter for the same job, Plastic PBT GF30 or Stainless Steel 17-4PH?

For the same stiffness or strength: Plastic PBT GF30 is lighter for a stiff beam (bending), stiff panel or plate, strong beam, strong panel or plate; Stainless Steel 17-4PH is lighter for a stiff rod or tie (tension), strong rod or tie.

Part that must be	Plastic PBT GF30	Stainless Steel 17-4PH
Stiff rod or tie (tension)	3.94x heavier	lighter
Stiff beam (bending)	lighter	14% heavier
Stiff panel or plate	lighter	1.87x heavier
Strong rod or tie	1.79x heavier	lighter
Strong beam	lighter	17% heavier
Strong panel or plate	lighter	1.69x heavier

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, Plastic PBT GF30 or Stainless Steel 17-4PH?

Stainless Steel 17-4PH conducts heat better: 17.9 W/m·K against 0.27 W/m·K for Plastic PBT GF30.

Which expands less with temperature?

Stainless Steel 17-4PH expands less: 10.8 µm/m·K against 25 µm/m·K for Plastic PBT GF30.

Among 72 materials

Stiffness against density

Strength against density