303 Stainless Steel (UNS S30300)
Austenitic (free-machining) · ASTM A582 · Density 7.93 g/cm³
Type 303 (UNS S30300) is the free-machining version of 304 stainless steel. Deliberately added sulfur (≥0.15%) forms manganese sulfide inclusions that break chips during cutting, roughly doubling machining rates at the cost of slightly lower corrosion resistance and poor weldability. It is the default austenitic grade for high-volume turned parts.
Chemical Composition (wt%)
| C | Mn | Si | Cr | Ni | P | S | Mo |
|---|---|---|---|---|---|---|---|
| ≤0.15 | ≤2.00 | ≤1.00 | 17.0–19.0 | 8.0–10.0 | ≤0.20 | ≥0.15 | ≤0.60 (optional) |
Single values are maximums unless a range is shown. Balance: Fe. Per ASTM A582.
Mechanical Properties
| Tensile strength (annealed, typical) | ≈620 MPa |
|---|---|
| Yield strength (0.2%, typical) | ≈240 MPa |
| Elongation (50 mm, typical) | ≈50% |
| Hardness | ≤262 HBW |
Room-temperature values are summarized for the product form and condition represented by ASTM A582; confirm section size, delivery condition and current governing edition before ordering.
Physical Properties & Structure
| Density | 7.93 g/cm³ |
|---|---|
| Magnetic response | Essentially non-magnetic after solution annealing; cold work can introduce a measurable magnetic response. |
| Microstructure | Austenitic (free-machining) |
Corrosion Resistance & Limits
- General corrosion resistance comes from the chromium-rich passive film; nickel, molybdenum, nitrogen and copper change performance by grade.
- Check chlorides, temperature, crevices, deposits, process chemistry and cleaning conditions. A grade designation alone is not a service-life guarantee.
Fabrication & Heat Treatment
| Welding | Generally weldable with a qualified procedure and matching or over-alloyed filler where required; remove heat tint when corrosion service demands it. |
|---|---|
| Forming | Good ductility is typical, but rapid work hardening increases forming load and springback; bend radius and intermediate annealing depend on grade and reduction. |
| Machining | Use rigid tooling, positive feeds and controlled heat because the material work-hardens; free-machining grades require separate corrosion and welding review. |
| Heat treatment | Solution annealing and rapid cooling restore the intended condition where applicable. Austenitic grades are not hardened by conventional quench-and-temper treatment. |
Equivalent Grades
The closest international equivalents of 303 Stainless Steel are 1.4305 (X8CrNiS18-9) in the EN system, SUS303 in the JIS system, Y12Cr18Ni9 in the GB system.
These are common corresponding designations, not unconditional substitutes. Verify chemistry, mechanical properties, product standard, delivery condition, dimensions and project approval before changing designation.
| System | Designation |
|---|---|
| UNS | S30300 |
| EN | 1.4305 (X8CrNiS18-9) |
| JIS | SUS303 |
| GB | Y12Cr18Ni9 |
Reference Product Forms & Dimensional Ranges
Common reference product forms for 303 stainless steel: Bar.
| Bar diameter | 3–150 mm |
|---|---|
| Condition | Annealed, cold drawn; smooth turned or polished on request |
| Length | 3 m / 6 m fixed lengths |
Common surface and delivery options: Hot rolled, peeled, bright drawn, ground or polished bar condition according to tolerance.
These published ranges are engineering references, not a live-stock or production-capability promise. Confirm the required product form, dimensions, condition, finish and supply route in the quotation.
Typical Applications
- Precision turned components
- Fittings, bushings and couplings
- Valve and pump internals
- Screw-machine products and fasteners
- Gears and shafts
Frequently Asked Questions
Can 303 stainless steel be welded?
Welding is not recommended. The same sulfur that makes 303 machinable causes hot cracking in the weld and heat-affected zone. If a machined part must also be welded, switch to 304L and accept the slower machining, or redesign the joint mechanically.
Is 303 as corrosion resistant as 304?
Not quite. The manganese sulfide inclusions act as initiation sites for pitting, so 303 gives up some resistance, most noticeably in wet, chloride or acidic service. Indoors and in dry mechanical service the difference is rarely significant.
When should I choose 303 over 304?
Choose 303 when machining time dominates part cost — high-volume turned fittings, bushings and valve bodies made on screw machines. Choose 304 whenever the part is welded, heavily cold formed, or exposed to chlorides or product-contact hygiene requirements.
303 Compared With Other Grades
Organizational author: Tsingshan (Shandong) Iron & Steel Co., Ltd..Review method, status and limitations.
Other stainless steel grades:
304304L316316L201321310S4104302205202301309S316Ti347904L409L4204394414442507317L254 SMO440C17-4 PH2304
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