Stainless Steel 321 vs 660
Stainless Steel · grade comparison
Stainless Steel 321 and 660 are both stainless steel grades, both heat resistant ss. 660 is the stronger of the two: yield strength 310 MPa (45 ksi) against 240 MPa (34.8 ksi) for 321, about 29% more; tensile strength follows at 690 MPa (100 ksi) vs 620 MPa (89.9 ksi). In exchange, 321 is the more ductile: elongation 45% versus 40% for 660, and 660 is harder (160 HB vs 150 HB). 321 runs hotter in service (870°C vs 540°C continuous) and 321 conducts heat better (16.1 W/m·K vs 13.4 W/m·K). On the shop floor, 321 machines more easily (fair vs poor), 321 welds better (excellent vs good), and 660 sits in a lower cost tier (premium, $$$) than 321 (high, $$$$).
321Choose it when the part is bent, formed or impact-loaded, or when the part sees heat.
660Choose it when strength drives the design, or when cost is the deciding factor.
321 vs 660: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all stainless 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 stainless 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
Bulk Modulus
Poisson's Ratio
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)
Hardness, Brinell
Hardness, Rockwell B
Hardness, Vickers
Same in both: Shear Modulus 77 GPa11.2 Msi · Charpy V-Notch Impact (RT) 120 J88.5 ft·lbf
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
Specific Heat Capacity
Latent Heat of Fusion
Max Service Temperature (continuous)
Same in both: Thermal Expansion (CTE, 20–100 °C) 16.6 µm/m·K9.2 µin/in·°F · Min Service Temperature -196°C-321 °F
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)
Brazeability / Solderability
Polishability
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Typical Recycled Content
Same in both: Embodied Water 200 L/kg24 gal/lb
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Modulus of Resilience
Thermal Diffusivity
Same in both: Thermal Shock Resistance Index 3
Strength versus weight
Yield strength against density for every stainless steel grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | 321 | 660 |
|---|---|---|
| Default condition | Solution Annealed | Solution Annealed |
| Relative cost | $$$$ High | $$$ Premium |
| 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 32 finishes: AlCrN, AlTiN, Black Oxide, CVD Al2O3, CVD TiCN, CVD TiN, Cerakote, Chrome Plating, CrN, DLC, Electroless Nickel (EN), Electropolishing and 20 more.
321 vs 660 — frequently asked
Is 660 stronger than 321?
Yes. 660 has a typical yield strength of 310 MPa (45 ksi) against 240 MPa (34.8 ksi) for 321 — about 29% more. Tensile strength is 690 MPa (100 ksi) vs 620 MPa (89.9 ksi).
Which is cheaper, 321 or 660?
660 is the lower-cost material: it sits in the premium tier ($$$) while 321 is high ($$$$). 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, 321 or 660?
321. Its machinability rates fair (38/100) against poor (28/100) for 660; for welding the order is 321 first (excellent, 88/100) then 660 (good, 55/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 321 and 660 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.