Steel 18CrNi8 vs 5120
Steel · grade comparison
Steel 18CrNi8 and 5120 are both steel grades, both case hardening steel. 18CrNi8 is the stronger of the two: yield strength 570 MPa (82.7 ksi) against 295 MPa (42.8 ksi) for 5120, about 93% more; tensile strength follows at 870 MPa (126 ksi) vs 470 MPa (68.2 ksi). In exchange, 5120 is the more ductile: elongation 25% versus 13% for 18CrNi8, and 18CrNi8 is harder (255 HB vs 145 HB). 5120 runs hotter in service (350°C vs 200°C continuous) and 5120 conducts heat better (46 W/m·K vs 34 W/m·K). On the shop floor, 5120 machines more easily (good vs fair) and 5120 welds better (good vs poor).
18CrNi8Choose it when strength drives the design.
5120Choose it when the part is bent, formed or impact-loaded, or when the part sees heat.
18CrNi8 vs 5120: 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
Bulk Modulus
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 C
Hardness, Vickers
Hardness, Rockwell B
Same in both: Shear Modulus 80 GPa11.6 Msi · Poisson's Ratio 0.29
Physical
Density and transition temperatures.
Liquidus Temperature
Same in both: Density 7.85 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,420°C2,588 °F
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Specific Heat Capacity
Thermal Expansion (CTE, 20–100 °C)
Max Service Temperature (continuous)
Min Service Temperature
Same in both: 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)
Same in both: 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)
Brazeability / Solderability
Polishability
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Embodied Water
Same in both: Typical Recycled Content 30%
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 | 18CrNi8 | 5120 |
|---|---|---|
| Default condition | HR | HR |
| Relative cost | $$ Standard | $$ Standard |
| Min. machined wall | 0.8 mm | 0.8 mm |
| Best machined surface | Ra 1.6 µm | Ra 1.6 µm |
Both are offered for CNC machining and Sheet metal. Both take the same 38 finishes: AlCrN, AlTiN, Black Oxide, CVD Al2O3, CVD TiCN, CVD TiN, Cerakote, Chrome Plating, Copper Plating, CrN, DLC, E-Coating and 26 more.
18CrNi8 vs 5120 — frequently asked
Is 18CrNi8 stronger than 5120?
Yes. 18CrNi8 has a typical yield strength of 570 MPa (82.7 ksi) against 295 MPa (42.8 ksi) for 5120 — about 93% more. Tensile strength is 870 MPa (126 ksi) vs 470 MPa (68.2 ksi).
Which is cheaper, 18CrNi8 or 5120?
Both sit in the same relative cost tier ($$, standard); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which is easier to machine, 18CrNi8 or 5120?
5120. Its machinability rates good (62/100) against fair (40/100) for 18CrNi8; for welding the order is 5120 first (good, 60/100) then 18CrNi8 (poor, 30/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 18CrNi8 and 5120 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.