Gear Material Properties: Density, Modulus and Thermal Data
Blog 2026-09-20
Gear material properties—density, elastic modulus, Poisson’s ratio, and thermal conductivity—affect a gear even before machining begins. They determine blank weight and inertia, tooth deflection under load, and how much cutting heat remains in the workpiece instead of leaving with the chip.
The tables below collect values for the materials used most often in gear work, including steels and cast irons, non-ferrous alloys, and engineering polymers for light-duty gears. All values are metric. Density is given in g/cm³. Multiply by 1000 to convert it to kg/m³.
Quick answers
| Question | Answer |
|---|---|
| Density of carbon steel | 7.81 to 7.85 g/cm³ |
| Density of alloy steel | 7.9 g/cm³ |
| Density of cast steel | 7.8 g/cm³ |
| Density of grey cast iron | 7.0 g/cm³ |
| Elastic modulus of steel | 206 GPa |
| Shear modulus of steel | 79.4 GPa |
| Poisson’s ratio of steel | 0.30 |
| Thermal conductivity of carbon steel | 47 to 58 W/(m·K) at 0 to 100 °C |
| Thermal conductivity of austenitic stainless steel (304 / 316) | 14 to 16 W/(m·K) at 0 to 100 °C |
| Thermal conductivity of martensitic stainless steel (AISI 420) | about 25 W/(m·K) |
| Density of AISI 420 stainless steel | 7.7 to 7.8 g/cm³ |
| Elastic modulus of AISI 420 stainless steel | 200 to 215 GPa |
| Melting point of carbon steel | about 1460 °C |
| Melting point of austenitic stainless steel | about 1450 °C |
How these properties affect gears
Density
Density determines blank weight. Blank weight affects raw material cost, rotating inertia, and shipping weight.
For a 100 mm gear with a 30 mm face width, changing from aluminium at 2.7 g/cm³ to steel at 7.85 g/cm³ increases the blank mass by nearly three times. In high-speed gearing, rotating mass also affects the torque required for acceleration and deceleration. This is one reason aluminium and polymer gears are used in some low-torque, high-acceleration positions.
Density is therefore relevant at both the design and manufacturing stages. It affects the amount of material used, the weight of the finished component, and the dynamic behavior of a rotating gear.
Thermal conductivity
Thermal conductivity has a direct effect on cutting and grinding because it determines how quickly heat can move through the material.
Austenitic stainless steel such as 304 and 316 has a thermal conductivity of roughly 14 to 16 W/(m·K). Carbon steel is around 47 to 58 W/(m·K) over the same temperature range. Martensitic stainless steel such as AISI 420 is around 25 W/(m·K).
The difference matters when machining gear teeth. Lower thermal conductivity means that less heat can move away through the workpiece and cutting chip, leaving more heat near the cutting edge.
The practical effects include:
- Higher cutting-edge temperature and faster tool wear
- Greater tendency toward work hardening when the surface reaches conditions that promote hardening before the tool cuts below the hardened layer
- Greater tendency for built-up edge
- Higher grinding heat concentration and greater risk of grinding burn on hardened tooth flanks
This is why AISI 420 and 4140 may require different cutting parameters even when their hardness is comparable. Their thermal and machining characteristics are different.
Elastic modulus and shear modulus
Elastic modulus describes how much a material deforms elastically under load. In gears, this affects tooth deflection, mesh stiffness, load sharing and vibration behavior.
Steel has an elastic modulus of about 206 GPa. Grey cast iron is around 118 to 126 GPa, or roughly 60 percent of the value for steel. Grey cast iron also has higher damping characteristics, which can influence the vibration behavior of cast iron gears.
Material substitution therefore needs to be treated as a design change rather than a simple material replacement. Changing a gear from steel to cast iron or aluminium changes tooth deflection at the same load and can affect contact stress and load sharing.
Poisson’s ratio
Poisson’s ratio describes lateral contraction when a material is loaded in tension. It is used in contact stress calculations together with elastic and shear modulus.
For steel, Poisson’s ratio is close to 0.30 and does not usually change a gear design on its own. It becomes more significant when a polymer replaces a metallic gear because polymer materials generally have different elastic behavior.
Melting point
Melting point is mainly a reference value for gear materials. Normal gear operation does not take place anywhere near the melting point of steel.
For finished gears, the useful temperature limits are more closely related to heat treatment and tempering conditions than to melting. Melting point is still useful when considering processes such as coating or brazing, and when comparing it with the temperatures associated with grinding burn.
Ferrous materials
| Material | Density (g/cm³) | E (GPa) | G (GPa) | Poisson’s ratio | Melting point (°C) | Thermal conductivity (W/(m·K)) | Specific heat (kJ/(kg·K)) |
|---|---|---|---|---|---|---|---|
| Carbon steel | 7.81 to 7.85 | 206 | 79.4 | 0.30 | 1460 | 47 to 58 | 0.49 |
| Cast steel | 7.8 | 202 | 0.30 | ||||
| Alloy steel | 7.9 | 206 | 79.4 | 0.30 | |||
| Nickel-chromium steel | 7.9 | 206 | 79.4 | 0.30 | |||
| Stainless steel, austenitic (304 / 316) | 7.9 to 8.0 | 193 to 200 | 77 | 0.29 to 0.30 | 1400 to 1450 | 14 to 16 | 0.50 |
| Stainless steel, martensitic (AISI 420) | 7.7 to 7.8 | 200 to 215 | 78 | 0.28 | 1425 to 1510 | 25 | 0.46 |
| Grey cast iron | 7.0 | 118 to 126 | 44.3 | 0.30 | 1200 | 58 | 0.532 |
| White cast iron | 7.55 | ||||||
| Malleable cast iron | 7.3 | ||||||
| Ductile iron | 173 | 0.30 | |||||
| Silicon steel sheet | 7.55 to 7.8 | ||||||
| High speed steel, 9% W | 8.3 | ||||||
| High speed steel, 18% W | 8.7 | ||||||
| Cemented carbide, WC-Co | 14.4 to 14.9 | 600 | 250 | 0.22 | not applicable | 81 | 0.80 |
| Cemented carbide, WC-TiC-Co | 9.5 to 12.4 |
Blank cells mean the source table does not carry that value.
Non-ferrous materials
| Material | Density (g/cm³) | E (GPa) | G (GPa) | Poisson’s ratio | Melting point (°C) | Thermal conductivity (W/(m·K)) | Specific heat (kJ/(kg·K)) |
|---|---|---|---|---|---|---|---|
| Aluminium, commercial | 2.7 | 68 | 25.3 to 26.5 | 0.32 to 0.36 | 658 | 204 | 0.879 |
| Aluminium wire, drawn | 69 | ||||||
| Duralumin | 70 | 26.5 | 0.30 | ||||
| Magnesium alloy | 1.74 | ||||||
| Copper, rolled | 8.9 | 108 | 39.2 | 0.31 to 0.34 | 1083 | 384 | 0.394 |
| Copper, cold drawn | 127 | 48.0 | |||||
| Brass, rolled | 8.4 to 8.85 | 89 to 97 | 34.3 to 36.3 | 0.32 to 0.42 | 950 | 104.7 | 0.384 |
| Brass, cast | 8.62 | ||||||
| Tin bronze | 8.7 to 8.9 | 103 | 0.30 | 910 | 64 | 0.37 | |
| Aluminium bronze, cast | 103 | 41.1 | 0.30 | ||||
| Phosphor bronze and cold drawn bronze | 8.8 | 113 | 41.2 | 0.32 to 0.35 | |||
| Manganese bronze, rolled | 108 | 39.2 | 0.35 | ||||
| Nickel | 8.9 | 1452 | 59 | 0.64 | |||
| Zinc, rolled | 7.1 | 82 | 31.4 | 0.27 | 419.5 | 110 to 113 | 0.38 |
| Tin | 7.29 | 232 | 64 | 0.24 | |||
| Lead | 11.37 | 16 | 6.8 | 0.42 | 327.4 | 34.7 | 0.13 |
| Bearing alloy, tin based | 7.34 to 7.75 | ||||||
| Bearing alloy, lead based | 9.33 to 10.67 |
Engineering polymers and composites
| Material | Density (g/cm³) | E (GPa) | G (GPa) | Poisson’s ratio | Thermal conductivity (W/(m·K)) |
|---|---|---|---|---|---|
| Polyamide, nylon 6 | 1.13 to 1.14 | 0.31 | |||
| Polyamide, nylon 66 | 1.14 to 1.15 | 0.31 | |||
| Polyamide, nylon 1010 | 1.04 to 1.06 | 1.07 | 0.31 | ||
| Phenolic laminate | 1.3 to 1.45 | ||||
| Phenolic cloth laminate | 3.92 to 8.83 | ||||
| Bakelite, unfilled | 1.2 | 1.96 to 2.91 | 0.69 to 2.06 | 0.35 to 0.38 | |
| Bakelite and fibre sheet | 1.3 to 1.4 | ||||
| PVC, rigid | 1.35 to 1.40 | 3.11 to 3.92 | 0.34 to 0.35 | 0.16 | |
| Polystyrene | 0.91 | ||||
| Acrylic, PMMA | 1.18 to 1.19 | 2.4 to 3.3 | |||
| PTFE | 1.14 to 1.42 | ||||
| Polyethylene, LDPE | 0.147 to 0.245 | ||||
| Polyethylene, HDPE | 0.54 to 0.75 | ||||
| Celluloid | 1.4 | 1.71 to 1.89 | 0.69 to 0.98 | 0.40 | |
| Rubber, pure | 0.93 | 0.0078 | 0.47 | ||
| Glass | 55 | 1.96 | 0.25 |
Reading the data for gear work
A material property should not be considered in isolation.
Density is useful when weight and rotating inertia matter. Elastic modulus and shear modulus become more relevant when tooth deflection, mesh stiffness and load sharing are involved. Poisson’s ratio enters contact stress calculations. Thermal conductivity becomes more important when the material is being cut or ground, especially in operations where heat removal is limited.
The same gear geometry can behave differently after a material change because the material properties change with it. This applies to both service behavior and manufacturing conditions.
For that reason, the values in the tables are best used as reference data during initial material selection, gear design and process planning. Grade-specific data should be checked against the relevant material certificate or supplier datasheet before it is used for a final engineering decision.
Notes on the data
1. Cemented carbide has no melting point. Cemented carbide is a composite of tungsten carbide grains in a cobalt binder. The binder softens and flows long before the carbide phase melts, so a single melting figure does not describe the supplied material. The table therefore marks the value as not applicable rather than assigning a number that could be misleading.
2. Stainless steel runs in two families. Thermal conductivity for austenitic grades such as 304 and 316 sits between 14 and 16 W/(m·K) across the 0 to 100 °C range and rises as temperature rises. Martensitic grades such as AISI 420 conduct heat better, at around 25 W/(m·K). Applying the austenitic figure to a martensitic gear can lead to cutting parameters that are more conservative than necessary.
3. What is not listed. Building materials, refractories, wood, leather and conveyor belting appeared in the source tables but are omitted here because they have no direct bearing on gear design.
4. Units. Density is given in g/cm³. Multiply by 1000 to convert to kg/m³. Thermal conductivity is given in W/(m·K). Specific heat is given in kJ/(kg·K). To convert °C to °F, multiply by 1.8 and add 32.
Need a value that is not listed?
A gear material not included in this table may need grade-specific data, especially for materials such as AISI 420. The relevant material grade and application determine how the published property values should be interpreted during gear design and machining.
