Stainless Steel 303 vs 304
Stainless Steel · grade comparison
Stainless Steel 303 and 304 are both stainless steel grades. 303 is the stronger of the two: yield strength 450 MPa (65.3 ksi) against 250 MPa (36.3 ksi) for 304, about 80% more; tensile strength follows at 655 MPa (95 ksi) vs 585 MPa (84.8 ksi). In exchange, 304 is the more ductile: elongation 55% versus 30% for 303, and 303 is harder (240 HB vs 150 HB). 304 runs hotter in service (870°C vs 760°C continuous). On the shop floor, 303 machines more easily (very good vs fair), 304 welds better (excellent vs poor), and 304 sits in a lower cost tier (standard, $$) than 303 (premium, $$$).
303Choose it when strength drives the design, or when the part is machined in volume.
304Choose it when the part is bent, formed or impact-loaded, or when the part sees heat.
Buyer's decision notes
Choose 303 bar for repetitive turned or milled parts when chip control and machine time dominate. Choose 304 when welding, forming, broader corrosion resistance or flat-rolled product availability matters more than free-machining behavior.
Compare the same condition
These base-grade routes do not fix condition or form. Normalize 303 free-machining bar against 304 bar in a comparable finish and diameter for a machining decision; use 304 sheet data separately for fabricated-sheet decisions.
- Chip control
- 303 uses a resulfurized free-machining route to improve chip breaking. That advantage is most valuable on high-volume bar-fed features; it may add little to a waterjet or sheet-fabrication part.
- Welding and forming
- The inclusions that help 303 machining reduce its suitability for welded and heavily formed designs. If the part needs structural welds, deep forming or aggressive flaring, start from 304 or another qualified fabrication grade.
- Corrosion and finish
- Do not assume all “18-8 stainless” grades behave alike after machining. Sulfur-bearing 303 generally gives up corrosion margin to 304, while tool smearing, heat tint, iron contamination and surface finish also affect the completed part.
- Product specification
- ASTM A582 covers free-machining stainless bar, while A276 covers more general stainless bars and shapes. Put the intended product specification on the order so chemistry, condition and inspection do not default to a stockist description.
Put this on the RFQ
- Specify bar form, size, finish, condition, ASTM A582 for 303 or the applicable 304 product specification, and certification level.
- Provide annual volume, machine type, chip-control need, critical surface finish and any cross-hole or thread features that drive cycle time.
- Identify every weld, cold-formed feature, corrosive medium and cleaning or passivation requirement before approving 303.
Primary references
- Outokumpu — Prodec 303 machining guide — Producer guide describing 303 as a resulfurized free-machining austenitic bar grade and its product forms.
- ASTM — A582/A582M — Active specification for free-machining stainless steel bars.
FabDigit resources: 303 datasheet, 304 datasheet, CNC design guide and sheet-metal design guide.
303 vs 304: 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.
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 B
Hardness, Vickers
Same in both: Elastic (Young's) Modulus 193 GPa28 Msi · Shear Modulus 77 GPa11.2 Msi · Poisson's Ratio 0.29
Physical
Density and transition temperatures.
Density
Liquidus Temperature
Same in both: Melting Point (Solidus) 1,400°C2,552 °F
Thermal
How each material carries heat and how hot it can run.
Latent Heat of Fusion
Max Service Temperature (continuous)
Min Service Temperature
Same in both: Thermal Conductivity 16.2 W/m·K9.4 BTU/hr·ft·°F · Specific Heat Capacity 500 J/kg·K0.12 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 17.3 µm/m·K9.6 µin/in·°F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 2.4 % IACS · Electrical Resistivity 7.2×10⁻⁷ Ω·m28.3 µΩ·in
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 Carbon (primary production)
Embodied Water
Typical Recycled Content
Same in both: Embodied Energy (primary production) 53 MJ/kg22,786 BTU/lb
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Modulus of Resilience
Same in both: Thermal Diffusivity 4.1 mm²/s · 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 | 303 | 304 |
|---|---|---|
| Sheet metal | — | Yes |
| Casting & forging | — | Yes |
| Default condition | Cold Drawn | Annealed |
| Relative cost | $$$ Premium | $$ 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. 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.
303 vs 304 — frequently asked
Is 303 stronger than 304?
Yes. 303 has a typical yield strength of 450 MPa (65.3 ksi) against 250 MPa (36.3 ksi) for 304 — about 80% more. Tensile strength is 655 MPa (95 ksi) vs 585 MPa (84.8 ksi).
Which is cheaper, 303 or 304?
304 is the lower-cost material: it sits in the standard tier ($$) while 303 is premium ($$$). 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, 303 or 304?
303. Its machinability rates very good (72/100) against fair (45/100) for 304; for welding the order is 304 first (excellent, 88/100) then 303 (poor, 25/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 303 and 304 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.