Steel P21 vs P3
Steel · grade comparison
Steel P21 and P3 are both steel grades. P21 is the stronger of the two: yield strength 1,150 MPa (167 ksi) against 340 MPa (49.3 ksi) for P3, about 3.4 times as much; tensile strength follows at 1,300 MPa (189 ksi) vs 540 MPa (78.3 ksi). In exchange, P3 is the more ductile: elongation 28% versus 14% for P21, and P21 is harder (375 HB vs 160 HB). P21 runs hotter in service (450°C vs 400°C continuous) and P3 conducts heat better (40 W/m·K vs 33 W/m·K). On the shop floor, P3 machines more easily (good vs fair), P3 welds better (65 vs 55 out of 100), and P3 sits in a lower cost tier (standard, $$) than P21 (premium, $$$).
P21Choose it when strength drives the design, or when the part sees heat.
P3Choose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
P21 vs P3: 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.
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: Elastic (Young's) Modulus 205 GPa29.7 Msi · Shear Modulus 80 GPa11.6 Msi · Poisson's Ratio 0.29
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
Thermal Expansion (CTE, 20–100 °C)
Max Service Temperature (continuous)
Min Service Temperature
Same in both: Specific Heat Capacity 460 J/kg·K0.11 BTU/lb·°F · 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).
Corrosion Resistance
Same in both: Galvanic Potential (seawater, vs SCE) -0.6 V
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
Same in both: Castability 35 / 100
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 | P21 | P3 |
|---|---|---|
| Default condition | — | — |
| Relative cost | $$$ Premium | $$ Standard |
| Min. machined wall | — | — |
| Best machined surface | — | — |
Both take the same 9 finishes: Copper Plating, Electroless Nickel (EN), Epoxy Coating, Gold Plating, Hard Chrome Plating, Manganese Phosphate, Plasma Spray, Silver Plating, Zinc Phosphate.
P21 vs P3 — frequently asked
Is P21 stronger than P3?
Yes. P21 has a typical yield strength of 1,150 MPa (167 ksi) against 340 MPa (49.3 ksi) for P3 — about 3.4 times as much. Tensile strength is 1,300 MPa (189 ksi) vs 540 MPa (78.3 ksi).
Which is cheaper, P21 or P3?
P3 is the lower-cost material: it sits in the standard tier ($$) while P21 is premium ($$$). 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, P21 or P3?
P3. Its machinability rates good (62/100) against fair (45/100) for P21; for welding the order is P3 first (good, 65/100) then P21 (good, 55/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in P21 and P3 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.