Steel P21 Nitrided vs P21-ST
Steel · P21 temper comparison
P21 Nitrided and P21-ST are two conditions of the same steel grade, P21: Nitrided versus ST (solution annealed). The chemistry is identical, so every difference below comes from the condition. P21 Nitrided is the stronger of the two: yield strength 1,150 MPa (167 ksi) against 740 MPa (107 ksi) for P21-ST, about 55% more; tensile strength follows at 1,300 MPa (189 ksi) vs 950 MPa (138 ksi). In exchange, P21-ST is the more ductile: elongation 18% versus 11% for P21 Nitrided, and P21 Nitrided is harder (375 HB vs 285 HB). On the shop floor, P21-ST machines more easily (good vs not recommended) and P21-ST welds better (good vs not recommended).
P21 NitridedChoose it when strength drives the design.
P21-STChoose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
P21 Nitrided vs P21-ST: 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.
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
Same in both: Elastic (Young's) Modulus 205 GPa29.7 Msi · Shear Modulus 80 GPa11.6 Msi · Bulk Modulus 163 GPa23.6 Msi · Poisson's Ratio 0.29
Physical
Density and transition temperatures.
Same in both: Density 7.83 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,420°C2,588 °F · Liquidus Temperature 1,490°C2,714 °F
Thermal
How each material carries heat and how hot it can run.
Same in both: Thermal Conductivity 33 W/m·K19.1 BTU/hr·ft·°F · Specific Heat Capacity 460 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 12.4 µm/m·K6.9 µin/in·°F · Latent Heat of Fusion 270 J/g116 BTU/lb · Max Service Temperature (continuous) 450°C842 °F · Min Service Temperature -30°C-22 °F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 4.9 % IACS · Electrical Resistivity 3.5×10⁻⁷ Ω·m13.8 µΩ·in
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)
Same in both: Castability 35 / 100 · Brazeability / Solderability 40 / 100 · Polishability 70 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 34 MJ/kg14,617 BTU/lb · Embodied Carbon (primary production) 2.4 kg CO₂/kg · Embodied Water 60 L/kg7.2 gal/lb · Typical Recycled Content 30%
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.
P21 Nitrided vs P21-ST — frequently asked
Is P21 Nitrided stronger than P21-ST?
Yes. P21 Nitrided has a typical yield strength of 1,150 MPa (167 ksi) against 740 MPa (107 ksi) for P21-ST — about 55% more. Tensile strength is 1,300 MPa (189 ksi) vs 950 MPa (138 ksi).
Which condition does FabDigit quote by default, Nitrided or ST?
PH 38-42 HRC is the default P21 condition in the FabDigit quote flow (neither Nitrided nor ST). The other condition is available on request or by drawing note — specify it in the material field or the part notes and the quote is priced for it.
Which is easier to machine, P21 Nitrided or P21-ST?
P21-ST. Its machinability rates good (58/100) against not recommended (10/100) for P21 Nitrided; for welding the order is P21-ST first (good, 55/100) then P21 Nitrided (not recommended, 12/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in P21 Nitrided and P21-ST 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.