Steel 15B21 vs 5120
Steel · grade comparison
Steel 15B21 and 5120 are both steel grades, both case hardening steel. 5120 is the stronger of the two: yield strength 295 MPa (42.8 ksi) against 280 MPa (40.6 ksi) for 15B21, about 5% more. In exchange, 15B21 is the more ductile: elongation 28% versus 25% for 5120, and 5120 is harder (145 HB vs 131 HB). 15B21 runs hotter in service (400°C vs 350°C continuous) and 15B21 conducts electricity better (10 % IACS vs 7.8 % IACS). On the shop floor, 15B21 welds better (excellent vs good).
15B21Choose it when the part is bent, formed or impact-loaded, or when the part sees heat.
5120Choose it when strength drives the design.
15B21 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.
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Fatigue Strength (Endurance Limit)
Hardness, Brinell
Hardness, Rockwell B
Compressive Strength
Fracture Toughness (K_IC)
Hardness, Vickers
Same in both: Elastic (Young's) Modulus 205 GPa29.7 Msi · Shear Modulus 80 GPa11.6 Msi · Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.29 · Reduction in Area 55% · Shear Strength 300 MPa43.5 ksi · Charpy V-Notch Impact (RT) 60 J44.3 ft·lbf
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
Thermal Expansion (CTE, 20–100 °C)
Max Service Temperature (continuous)
Min Service Temperature
Same in both: Specific Heat Capacity 470 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) -0.61 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
Same in both: Polishability 55 / 100
Sustainability
Primary-production footprint per kilogram.
Embodied Carbon (primary production)
Embodied Water
Same in both: Embodied Energy (primary production) 25 MJ/kg10,748 BTU/lb · Typical Recycled Content 30%
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Modulus of Resilience
Thermal Diffusivity
Thermal Shock Resistance Index
Same in both: Specific Stiffness (E / density) 26.1 MN·m/kg
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 | 15B21 | 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.
15B21 vs 5120 — frequently asked
Is 5120 stronger than 15B21?
Yes. 5120 has a typical yield strength of 295 MPa (42.8 ksi) against 280 MPa (40.6 ksi) for 15B21 — about 5% more. Tensile strength is 470 MPa (68.2 ksi) vs 450 MPa (65.3 ksi).
Which is cheaper, 15B21 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, 15B21 or 5120?
5120, by a small margin. Both rate good for machinability — 62/100 against 55/100 for 15B21; for welding the order is 15B21 first (excellent, 85/100) then 5120 (good, 60/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 15B21 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.