Steel 4340 vs Fe-3Si
Steel · grade comparison
Steel 4340 and Fe-3Si are both steel grades. 4340 is the stronger of the two: yield strength 620 MPa (89.9 ksi) against 450 MPa (65.3 ksi) for Fe-3Si, about 38% more; tensile strength follows at 950 MPa (138 ksi) vs 550 MPa (79.8 ksi). 4340 is the more ductile: elongation 18% versus 3% for Fe-3Si, and 4340 is harder (285 HB vs 235 HB). 4340 runs hotter in service (400°C vs 350°C continuous) and 4340 conducts heat better (44.5 W/m·K vs 21 W/m·K). On the shop floor, 4340 machines more easily (48 vs 38 out of 100), Fe-3Si welds better (fair vs poor), and 4340 sits in a lower cost tier (premium, $$$) than Fe-3Si (high, $$$$).
4340Choose it when strength drives the design, or when the part is bent, formed or impact-loaded.
Fe-3SiChoose it when it will be welded.
4340 vs Fe-3Si: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all 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 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
Shear Modulus
Bulk Modulus
Poisson's Ratio
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Reduction in Area
Compressive Strength
Shear Strength
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell B
Hardness, Rockwell C
Hardness, Vickers
Physical
Density and transition temperatures.
Density
Melting Point (Solidus)
Liquidus Temperature
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Specific Heat Capacity
Thermal Expansion (CTE, 20–100 °C)
Latent Heat of Fusion
Max Service Temperature (continuous)
Min Service Temperature
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)
Castability
Brazeability / Solderability
Polishability
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Typical Recycled Content
Same in both: Embodied Water 60 L/kg7.2 gal/lb
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Modulus of Resilience
Thermal Diffusivity
Thermal Shock Resistance Index
Same in both: Specific Stiffness (E / density) 26.1 MN·m/kg
Strength versus weight
Yield strength against density for every steel grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | 4340 | Fe-3Si |
|---|---|---|
| CNC machining | Yes | — |
| Sheet metal | Yes | — |
| Default condition | HR | — |
| Relative cost | $$$ Premium | $$$$ High |
| Min. machined wall | 0.8 mm | — |
| Best machined surface | Ra 1.6 µm | — |
| AlCrN | Yes | — |
| AlTiN | Yes | — |
| Black Oxide | Yes | — |
| CVD Al2O3 | Yes | — |
| CVD TiCN | Yes | — |
| CVD TiN | Yes | — |
| Cerakote | Yes | — |
| Chrome Plating | Yes | — |
| CrN | Yes | — |
| DLC | Yes | — |
| E-Coating | Yes | — |
| HVOF Coating | Yes | — |
| Hot-Dip Galvanizing | Yes | — |
| MoS2 | Yes | — |
| Multilayer CVD | Yes | — |
| Nickel Plating | Yes | — |
| PTFE Coating | Yes | — |
| Painting | Yes | — |
They share 9 finishes: Copper Plating, Electroless Nickel (EN), Epoxy Coating, Gold Plating, Hard Chrome Plating, Manganese Phosphate, Plasma Spray, Silver Plating, Zinc Phosphate.
4340 vs Fe-3Si — frequently asked
Is 4340 stronger than Fe-3Si?
Yes. 4340 has a typical yield strength of 620 MPa (89.9 ksi) against 450 MPa (65.3 ksi) for Fe-3Si — about 38% more. Tensile strength is 950 MPa (138 ksi) vs 550 MPa (79.8 ksi).
Which is cheaper, 4340 or Fe-3Si?
4340 is the lower-cost material: it sits in the premium tier ($$$) while Fe-3Si 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, 4340 or Fe-3Si?
4340, by a small margin. Both rate fair for machinability — 48/100 against 38/100 for Fe-3Si; for welding the order is Fe-3Si first (fair, 50/100) then 4340 (poor, 33/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 4340 and Fe-3Si 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.