Stainless Steel 303
AISI/SAE 303 · UNS S30300 · EN 1.4305, X8CrNiS18-9 · JIS SUS303 · GB Y1Cr18Ni9, Y12Cr18Ni9
303 is the free-machining version of 18-8 austenitic stainless (S30300 / 1.4305), with 0.15–0.35 % sulfur forming manganese-sulfide inclusions that break chips and give roughly twice the machining rate of 304 (machinability 72/100).
Values for the Cold Drawn condition
303 tempers and conditions
303 is supplied in 5 conditions, soft to hard. Cold Drawn is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
hot rolled, annealed and pickled bar | Large-diameter or rough-turning stock where cold-drawn tolerance is unnecessary and cost matters. | 250 | 600 | 45 | 175 HB | 2.4 % IACS |
solution annealed (1010–1120 °C, water quenched) | Softest, most ductile and most corrosion-resistant condition; choose for cold heading, bending or when maximum ductility is needed. | 260 | 620 | 50 | 165 HB | — |
Cold DrawnDefault cold-finished (drawn) bar, ASTM A582 | Standard stocked condition for screw-machine bar: higher strength, tight size tolerance and the best chip control. | 450 | 655 | 30 | 240 HB | — |
cold drawn, centerless ground and polished bar (h9/h8) | Pick when a precise diameter and a smooth shaft surface are needed straight from stock (pins, spindles, shafts). | 450 | 655 | 30 | 23 HRC | 2.4 % IACS |
1/4 Hard | Higher-strength small-diameter bar and wire for fasteners where extra proof strength is required. | 620 | 860 | 15 | 29 HRC | 2.4 % IACS |
What is 303?
303 is the free-machining version of 18-8 austenitic stainless (S30300 / 1.4305), with 0.15–0.35 % sulfur forming manganese-sulfide inclusions that break chips and give roughly twice the machining rate of 304 (machinability 72/100). It is supplied mainly as cold-drawn bright bar for high-volume turned parts such as nuts, shafts, valve parts and fittings. The sulfur costs corrosion resistance — pitting resistance is below 304 — plus weldability (hot-cracking tendency), transverse ductility and polishability, so welded assemblies and chloride service should use 304L or 316. 303 has a density of 7.9 g/cm³ (0.285 lb/in³), heavier than 68% of stainless steel grades. It melts at 1,400°C (2,552 °F). 303 has a yield strength of 450 MPa (65.3 ksi) and a tensile strength of 655 MPa (95 ksi) — stronger than 70% of stainless steel grades. Elongation at break is 30% and the elastic modulus is 193 GPa (28 Msi).
What is 303 used for?
- CNC turned shafts
- Valve bodies and stems
- Nuts and threaded fittings
- Bushings and spacers
- Shaft couplings
- Instrument and connector bodies
Advantages
- Easy to machine — 72/100, better than 99% of stainless steel grades
Limitations
- Hard to polish — 40/100, worse than 99% of stainless steel grades
- Difficult to weld — 25/100, worse than 92% of stainless steel grades
- High embodied carbon — 5.5 kg CO₂/kg, worse than 77% of stainless steel grades
303 properties
Typical room-temperature values for 303-Cold Drawn; bars are the position among stainless steel grades.
Physical3
303 has a density of 7.9 g/cm³ (0.285 lb/in³), heavier than 68% of stainless steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
303 has a yield strength of 450 MPa (65.3 ksi) and a tensile strength of 655 MPa (95 ksi) — stronger than 70% of stainless steel grades. Elongation at break is 30% and the elastic modulus is 193 GPa (28 Msi).
Thermal6
303 is rated for continuous service to 760°C (1,400 °F). It conducts heat at 16.2 W/m·K (9.36 BTU/hr·ft·°F), better than 64% of stainless steel grades. Thermal expansion is 17.3 µm/m·K (9.61 µin/in·°F).
Electrical3
303 conducts electricity at 2.4 % IACS, better than 67% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (58/100), worse than 62% of stainless steel grades.
Sustainability4
Producing a kilogram of 303 takes about 53 MJ of energy and emits 5.5 kg of CO₂ — less than 67% of stainless steel grades. Typical recycled content is 65%.
Manufacturability7
303's machinability is very good (72/100, better than 99% of stainless steel grades); weldability poor (25/100); formability fair (40/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. 303 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 303
Is 303 easy to machine?
The best-machining austenitic stainless: run 30–50 % faster than 304 with sharp positive-rake tools, rigid setups and generous coolant; chips break cleanly thanks to MnS.
Can 303 be welded?
Not recommended — high sulfur promotes hot cracking and porosity; if unavoidable use 308L/312 filler, low heat input and no restraint, and expect reduced corrosion resistance.
Can 303 be formed, bent or molded?
Only light cold forming (thread rolling, mild bending); transverse ductility is poor and sulfide stringers open into cracks on tight bends — use 304 for deep drawing.
Manufacturability
The process limits FabDigit's quote engine applies to 303. Design inside these and the part quotes instantly; outside them it routes to an engineer.
CNC machining
| Machinability | Better72 / 100 |
|---|---|
| ISO material group | M.1 |
| Cutting speed (rough / finish) | 150 / 180 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1.5 mm |
| Drill depth limit | 4× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
303 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | ≤ 0.15 | 0.08 |
| Mncombines with S to form free-machining MnS | ≤ 2 | 1.5 |
| Si | ≤ 1 | 0.5 |
| P | ≤ 0.2 | 0.03 |
| Sdeliberate free-machining addition | 0.15 – 0.35 | 0.25 |
| Cr | 17 – 19 | 18 |
| Ni | 8 – 10 | 9 |
| Mooptional at producer's discretion (ASTM A582) | ≤ 0.6 | |
| Fe | balance |
What surface finishes work on 303?
Passivate per ASTM A967 (nitric or citric) after machining; electropolish improves pitting resistance, but a mirror polish is hard to achieve because sulfides pull out.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
Organic Coating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel 303 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- S30300
- EN / DIN / Werkstoff-Nr.
- 1.4305X8CrNiS18-9
- GB (China)
- Y1Cr18Ni9Y12Cr18Ni9
- JIS
- SUS303
- KS (Korea)
- STS303
How much does 303 cost?
303 is a premium-cost stainless steel ($$$), cheaper than about 60% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
303 — frequently asked
What is 303 used for?
303 is typically used for CNC turned shafts, valve bodies and stems, nuts and threaded fittings, bushings and spacers, shaft couplings and instrument and connector bodies. In short: easiest machining stainless.
What is the yield strength of 303?
303 has a typical yield strength of 450 MPa (65.3 ksi) and a tensile strength of 655 MPa (95 ksi) — stronger than 70% of stainless steel grades. Strength varies by condition: see the 5 listed tempers.
Is 303 easy to machine?
Yes — machinability is rated very good (72/100, better than 99% of stainless steel grades). The best-machining austenitic stainless: run 30–50 % faster than 304 with sharp positive-rake tools, rigid setups and generous coolant; chips break cleanly thanks to MnS.
Can 303 be welded?
Not readily — weldability is rated poor (25/100). Not recommended — high sulfur promotes hot cracking and porosity; if unavoidable use 308L/312 filler, low heat input and no restraint, and expect reduced corrosion resistance.
What surface finishes work on 303?
Passivate per ASTM A967 (nitric or citric) after machining; electropolish improves pitting resistance, but a mirror polish is hard to achieve because sulfides pull out.
Can 303 be formed, bent or molded?
Only light cold forming (thread rolling, mild bending); transverse ductility is poor and sulfide stringers open into cracks on tight bends — use 304 for deep drawing.
What is the maximum service temperature of 303?
303 is rated for continuous use to about 760°C (1,400 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does 303 cost?
303 is a premium-cost stainless steel ($$$), cheaper than about 60% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 303?
Yes — 303 is available for CNC machining with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A582/A582M Free-Machining Stainless Steel Bars — ASTM International (2021)
- EN 10088-3 Stainless steels — Semi-finished products, bars, rods (1.4305) — CEN (2014)
- GB/T 1220 (Y1Cr18Ni9) — SAC (2007)
- JIS G 4303 Stainless steel bars (SUS303) — JSA (2012)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
- Sandvik / Outokumpu free-machining austenitic grade datasheets — Sandvik, Outokumpu (2022)
- SMM / Mysteel — SMM, Mysteel (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.