Steel M4 vs M45
Steel · grade comparison
Steel M4 and M45 are both steel grades. M45 is the stronger of the two: yield strength 620 MPa (89.9 ksi) against 550 MPa (79.8 ksi) for M4, about 13% more; tensile strength follows at 950 MPa (138 ksi) vs 880 MPa (128 ksi). M45 is harder — 269 HB against 250 HB for M4 — which matters for wear surfaces and threads. M4 runs hotter in service (400°C vs 200°C continuous). On the shop floor, M45 sits in a lower cost tier (standard, $$) than M4 (specialty, $$$$$).
M4Choose it when the part sees heat.
M45Choose it when strength drives the design, or when surface hardness matters.
M4 vs M45: 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.
Poisson's Ratio
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Compressive Strength
Fracture Toughness (K_IC)
Hardness, Brinell
Hardness, Rockwell C
Hardness, Vickers
Fatigue Strength (Endurance Limit)
Charpy V-Notch Impact (RT)
Same in both: Elastic (Young's) Modulus 217 GPa31.5 Msi · Shear Modulus 84 GPa12.2 Msi · Bulk Modulus 165 GPa23.9 Msi · Elongation at Break 12% · Reduction in Area 25% · Shear Strength 600 MPa87 ksi
Physical
Density and transition temperatures.
Density
Melting Point (Solidus)
Same in both: Liquidus Temperature 1,420°C2,588 °F
Thermal
How each material carries heat and how hot it can run.
Thermal Expansion (CTE, 20–100 °C)
Max Service Temperature (continuous)
Same in both: Thermal Conductivity 22 W/m·K12.7 BTU/hr·ft·°F · Specific Heat Capacity 420 J/kg·K0.1 BTU/lb·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Min Service Temperature -60°C-76 °F
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 18 / 100
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Formability (cold)
Castability
Brazeability / Solderability
Polishability
Same in both: Machinability 25 / 100 · Machinability Rating (AISI 1212 = 100 %) 25% · Weldability 15 / 100
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Same in both: Embodied Carbon (primary production) 4.2 kg CO₂/kg · Embodied Water 110 L/kg13.2 gal/lb · Typical Recycled Content 35%
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 | M4 | M45 |
|---|---|---|
| CNC machining | Yes | — |
| Sheet metal | — | Yes |
| Default condition | Annealed | Annealed |
| Relative cost | $$$$$ Specialty | $$ 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 | — |
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.
M4 vs M45 — frequently asked
Is M45 stronger than M4?
Yes. M45 has a typical yield strength of 620 MPa (89.9 ksi) against 550 MPa (79.8 ksi) for M4 — about 13% more. Tensile strength is 950 MPa (138 ksi) vs 880 MPa (128 ksi).
Which is cheaper, M4 or M45?
M45 is the lower-cost material: it sits in the standard tier ($$) while M4 is specialty ($$$$$). Part price depends far more on geometry, tolerance and quantity than on raw stock — upload a CAD file for a live quote.
When should I choose M4 over M45?
Pick M4 when the part sees heat. Pick M45 when strength drives the design, or when surface hardness matters.
Ready to make it?
Upload a CAD file and FabDigit prices the part in M4 and M45 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.