Steel 4340 vs CP800
Steel · grade comparison
Steel 4340 and CP800 are both steel grades, both high strength steel. 4340 is the stronger of the two: tensile strength 950 MPa (138 ksi) against 840 MPa (122 ksi) for CP800, about 13% more. 4340 is the more ductile: elongation 18% versus 13% for CP800, and 4340 is harder (285 HB vs 250 HB). 4340 runs hotter in service (400°C vs 200°C continuous) and 4340 conducts heat better (44.5 W/m·K vs 38 W/m·K). On the shop floor, 4340 machines more easily (48 vs 35 out of 100), CP800 welds better (very good vs poor), and CP800 sits in a lower cost tier (standard, $$) than 4340 (premium, $$$).
4340Choose it when strength drives the design, or when the part is bent, formed or impact-loaded.
CP800Choose it when it will be welded, or when cost is the deciding factor.
4340 vs CP800: 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
Poisson's Ratio
Tensile Strength (Ultimate)
Elongation at Break
Compressive Strength
Shear Strength
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell C
Hardness, Vickers
Same in both: Shear Modulus 80 GPa11.6 Msi · Bulk Modulus 160 GPa23.2 Msi · Yield Strength (0.2% offset) 620 MPa89.9 ksi · Reduction in Area 45% · Hardness, Rockwell B 100 HRB
Physical
Density and transition temperatures.
Melting Point (Solidus)
Liquidus Temperature
Same in both: Density 7.85 g/cm³0.28 lb/in³
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)
Same in both: Min Service Temperature -40°C-40 °F
Electrical
Conductivity and insulation.
Electrical Conductivity
Electrical Resistivity
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Same in both: Galvanic Potential (seawater, vs SCE) -0.62 V · Corrosion Resistance 12 / 100
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Machinability Rating (AISI 1212 = 100 %)
Weldability
Formability (cold)
Castability
Polishability
Same in both: Brazeability / Solderability 55 / 100
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Embodied Water
Typical Recycled Content
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Modulus of Resilience
Thermal Diffusivity
Thermal Shock Resistance Index
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 | CP800 |
|---|---|---|
| CNC machining | Yes | — |
| Default condition | HR | CR |
| Relative cost | $$$ Premium | $$ Standard |
| Min. machined wall | 0.8 mm | — |
| Best machined surface | Ra 1.6 µm | — |
| AlCrN | Yes | — |
| AlTiN | Yes | — |
| CVD Al2O3 | Yes | — |
| CVD TiCN | Yes | — |
| CVD TiN | Yes | — |
| CrN | Yes | — |
| DLC | Yes | — |
| HVOF Coating | Yes | — |
| MoS2 | Yes | — |
| Multilayer CVD | Yes | — |
| TiAlN | Yes | — |
| TiB2 | Yes | — |
| TiCN | Yes | — |
| TiN | Yes | — |
| WC/C | Yes | — |
| ZrN | Yes | — |
Both are offered for Sheet metal. They share 22 finishes: Black Oxide, Cerakote, Chrome Plating, Copper Plating, E-Coating, Electroless Nickel (EN), Epoxy Coating, Gold Plating, Hard Chrome Plating, Hot-Dip Galvanizing, Manganese Phosphate, Nickel Plating and 10 more.
4340 vs CP800 — frequently asked
Is 4340 stronger than CP800?
Yes. 4340 has a typical tensile strength of 950 MPa (138 ksi) against 840 MPa (122 ksi) for CP800 — about 13% more.
Which is cheaper, 4340 or CP800?
CP800 is the lower-cost material: it sits in the standard tier ($$) while 4340 is premium ($$$). 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 CP800?
4340, by a small margin. Both rate fair for machinability — 48/100 against 35/100 for CP800; for welding the order is CP800 first (very good, 70/100) then 4340 (poor, 33/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 4340 and CP800 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.