Steel 42CrMo4 vs X8Ni9
Steel · grade comparison
Steel 42CrMo4 and X8Ni9 are both steel grades. X8Ni9 is the stronger of the two: yield strength 690 MPa (100 ksi) against 550 MPa (79.8 ksi) for 42CrMo4, about 25% more. X8Ni9 is the more ductile: elongation 24% versus 14% for 42CrMo4, and 42CrMo4 is harder (245 HB vs 215 HB). 42CrMo4 is stiffer (210 GPa vs 195 GPa) and 42CrMo4 runs hotter in service (400°C vs 350°C continuous). On the shop floor, 42CrMo4 machines more easily (50 vs 40 out of 100), X8Ni9 welds better (good vs fair), and 42CrMo4 sits in a lower cost tier (standard, $$) than X8Ni9 (premium, $$$).
42CrMo4Choose it when the part sees heat, or when the part is machined in volume.
X8Ni9Choose it when strength drives the design, or when the part is bent, formed or impact-loaded.
42CrMo4 vs X8Ni9: 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
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: Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.29
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)
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)
Polishability
Same in both: Brazeability / Solderability 50 / 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 | 42CrMo4 | X8Ni9 |
|---|---|---|
| CNC machining | Yes | — |
| Sheet metal | Yes | — |
| Default condition | HR | — |
| Relative cost | $$ Standard | $$$ Premium |
| 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.
42CrMo4 vs X8Ni9 — frequently asked
Is X8Ni9 stronger than 42CrMo4?
Yes. X8Ni9 has a typical yield strength of 690 MPa (100 ksi) against 550 MPa (79.8 ksi) for 42CrMo4 — about 25% more. Tensile strength is 745 MPa (108 ksi) vs 850 MPa (123 ksi).
Which is cheaper, 42CrMo4 or X8Ni9?
42CrMo4 is the lower-cost material: it sits in the standard tier ($$) while X8Ni9 is premium ($$$). 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, 42CrMo4 or X8Ni9?
42CrMo4, by a small margin. Both rate fair for machinability — 50/100 against 40/100 for X8Ni9; for welding the order is X8Ni9 first (good, 60/100) then 42CrMo4 (fair, 35/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 42CrMo4 and X8Ni9 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.