Stainless Steel E309LMo vs ER308Si
Stainless Steel · grade comparison
Stainless Steel E309LMo and ER308Si are both stainless steel grades. E309LMo is the stronger of the two: yield strength 430 MPa (62.4 ksi) against 400 MPa (58 ksi) for ER308Si, about 8% more. E309LMo is harder — 190 HB against 175 HB for ER308Si — which matters for wear surfaces and threads. ER308Si runs hotter in service (760°C vs 400°C continuous). On the shop floor, ER308Si forms better (good vs fair) and ER308Si sits in a lower cost tier (premium, $$$) than E309LMo (high, $$$$).
E309LMoChoose it when strength drives the design, or when surface hardness matters.
ER308SiChoose it when the part sees heat, or when cost is the deciding factor.
E309LMo vs ER308Si: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all stainless steel grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all stainless steel grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Bulk Modulus
Yield Strength (0.2% offset)
Elongation at Break
Reduction in Area
Compressive Strength
Shear Strength
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell B
Hardness, Vickers
Same in both: Shear Modulus 77 GPa11.2 Msi · Poisson's Ratio 0.29 · Tensile Strength (Ultimate) 600 MPa87 ksi · Fatigue Strength (Endurance Limit) 240 MPa34.8 ksi · Fracture Toughness (K_IC) 140 MPa·√m127 ksi·√in
Physical
Density and transition temperatures.
Density
Same in both: Melting Point (Solidus) 1,400°C2,552 °F · Liquidus Temperature 1,450°C2,642 °F
Thermal
How each material carries heat and how hot it can run.
Thermal Expansion (CTE, 20–100 °C)
Max Service Temperature (continuous)
Min Service Temperature
Same in both: Thermal Conductivity 15 W/m·K8.7 BTU/hr·ft·°F · Specific Heat Capacity 500 J/kg·K0.12 BTU/lb·°F · Latent Heat of Fusion 270 J/g116 BTU/lb
Electrical
Conductivity and insulation.
Electrical Conductivity
Electrical Resistivity
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Galvanic Potential (seawater, vs SCE)
Corrosion Resistance
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Machinability Rating (AISI 1212 = 100 %)
Weldability
Formability (cold)
Polishability
Brazeability / Solderability
Sustainability
Primary-production footprint per kilogram.
Embodied Carbon (primary production)
Embodied Water
Typical Recycled Content
Same in both: Embodied Energy (primary production) 55 MJ/kg23,646 BTU/lb
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Modulus of Resilience
Same in both: Thermal Diffusivity 3.8 mm²/s · Thermal Shock Resistance Index 3
Strength versus weight
Yield strength against density for every stainless steel grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | E309LMo | ER308Si |
|---|---|---|
| Default condition | — | — |
| Relative cost | $$$$ High | $$$ Premium |
| Min. machined wall | — | — |
| Best machined surface | — | — |
Both take the same 7 finishes: Electroless Nickel (EN), Epoxy Coating, Gold Plating, Hard Chrome Plating, Pickling, Plasma Spray, Silver Plating.
E309LMo vs ER308Si — frequently asked
Is E309LMo stronger than ER308Si?
Yes. E309LMo has a typical yield strength of 430 MPa (62.4 ksi) against 400 MPa (58 ksi) for ER308Si — about 8% more. Tensile strength is 600 MPa (87 ksi) vs 600 MPa (87 ksi).
Which is cheaper, E309LMo or ER308Si?
ER308Si is the lower-cost material: it sits in the premium tier ($$$) while E309LMo is high ($$$$). Part price depends far more on geometry, tolerance and quantity than on raw stock — upload a CAD file for a live quote.
Which is easier to machine, E309LMo or ER308Si?
ER308Si. Its machinability rates fair (40/100) against poor (32/100) for E309LMo; for welding the order is ER308Si first (excellent, 95/100) then E309LMo (excellent, 90/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in E309LMo and ER308Si side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.