JIS G4304/G4305 SUS303 Free
JIS G4304/G4305 SUS303 Free-Machining Austenitic Stainless Steel Plate & Coil
Comprehensive material data for SUS303 stainless steel plate and coil under JIS G4304 and G4305, including chemistry, mechanical, physical properties, equivalents, and application guidance.
Solution annealing, cold working, machining, stamping (limited), NOT suitable for welding or hot working in critical applications
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JIS G4304/G4305 SUS303 Free Introduction
SUS303 is a free-machining austenitic stainless steel specified in JIS G4304 (hot-rolled plates) and JIS G4305 (cold-rolled plates/coils). The addition of sulfur (min 0.15 %) transforms the grade into a highly machinable alloy while retaining the good corrosion resistance, non-magnetic nature, and formability typical of the 18Cr-8Ni austenitic family. Its machinability is significantly superior to SUS304, allowing faster cutting speeds, better chip breaking, and longer tool life. SUS303 is non-hardenable by heat treatment and is usually supplied in the solution-annealed condition. It cannot be hardened by quenching, but can be moderately strengthened by cold working. However, the presence of sulfur reduces its weldability and pitting resistance compared to standard 304 grades.
Main features:
- Excellent machinability (free-cutting)
- Good general corrosion resistance in mild environments
- Non-magnetic in annealed condition
- Good oxidation resistance up to 870 °C intermittent, 925 °C continuous
- Not recommended for welding due to hot cracking susceptibility
JIS G4304/G4305 SUS303 Free Chemical Composition
Chemical composition according to JIS G4304/G4305 for SUS303. Sulfur is intentionally added to improve machinability. Molybdenum is an optional alloying element permitted at the manufacturer's discretion. All other elements are specifications for the standard analysis.
| Element | Standard Value | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.15 | |
| Silicon (Si) | ≤ 1.00 | |
| Manganese (Mn) | ≤ 2.00 | |
| Phosphorus (P) | ≤ 0.20 | |
| Sulfur (S) | ≥ 0.15 | Min. 0.15 %, typically 0.15–0.35 % for machinability |
| Chromium (Cr) | 17.00 – 19.00 | |
| Nickel (Ni) | 8.00 – 10.00 | |
| Molybdenum (Mo) | ≤ 0.60 | Optional addition, may be present |
| Iron (Fe) | Balance |
JIS G4304/G4305 SUS303 Free Thermal and Electrical Physical Properties
Typical physical properties for SUS303 (UNS S30300 / 1.4305). These are not specified in JIS standards but are widely accepted engineering data for this alloy.
| Property | Standard Requirement | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 8.03 | g/cm³ | 20 °C |
| Elastic Modulus (E) | 193 | GPa | Tension, room temperature |
| Shear Modulus (G) | 77 | GPa | Torsion, room temperature |
| Poisson's Ratio (ν) | 0.25 | — | Room temperature |
| Thermal Expansion Coefficient (α) | 17.2 | 10⁻⁶ /K | 20–100 °C |
| Thermal Expansion Coefficient (α) | 17.8 | 10⁻⁶ /K | 20–300 °C |
| Thermal Expansion Coefficient (α) | 18.4 | 10⁻⁶ /K | 20–500 °C |
| Thermal Conductivity (λ) | 16.2 | W/m·K | 100 °C |
| Thermal Conductivity (λ) | 21.5 | W/m·K | 500 °C |
| Specific Heat Capacity | 500 | J/kg·K | 0–100 °C |
| Electrical Resistivity (ρ_e) | 0.72 | μΩ·m | 20 °C |
| Magnetic Permeability | ≤ 1.02 | — | Annealed, 200 H |
JIS G4304/G4305 SUS303 Free Mechanical Properties
Mechanical properties of SUS303 plate/coil in solution-annealed condition as per JIS G4304. Values apply to hot-rolled material. Cold-rolled material to JIS G4305 exhibits similar properties after annealing. Hardness values are maximum limits.
| Property | Standard Requirement | Unit | Test Condition / Thickness Range |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 520 | MPa | Room temperature, plate thickness ≤ 160 mm |
| Yield Strength (ReH, 0.2 % offset) | ≥ 205 | MPa | Room temperature |
| Elongation (A) | ≥ 40 | % | Thickness ≤ 5 mm |
| Elongation (A) | ≥ 40 | % | Thickness 5–8 mm |
| Elongation (A) | ≥ 50 | % | Thickness 8–75 mm |
| Elongation (A) | ≥ 40 | % | Thickness 75–160 mm |
| Hardness (HB) | ≤ 187 | HB | Brinell hardness |
| Hardness (HRB) | ≤ 90 | HRB | Rockwell B hardness |
| Hardness (HV) | ≤ 200 | HV | Vickers hardness |
| Bend Test | Not specified | Usually not required for austenitic grades |
JIS G4304/G4305 SUS303 Free Direct Equivalent Standards and Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| Japan | JIS G4304/G4305 | SUS303 | Original specification |
| USA | ASTM A240/A240M | 303 (UNS S30300) | Chemical and property match |
| Europe (EU) | EN 10088-2/3 | 1.4305 (X8CrNiS18-9) | Identical composition and similar mechanicals |
| International | ISO 15510 | X8CrNiS18-9 | ISO equivalent |
| China | GB/T 1220 | Y12Cr18Ni9 (old Y1Cr18Ni9) | Free-machining austenitic equivalent |
| UK (obsolete) | BS 970-1 | 303S31 | Historic equivalent |
| France (obsolete) | NF A35-574 | Z8CNF18-09 | Historic equivalent |
JIS G4304/G4305 SUS303 Free Application Introduction
SUS303 is engineered for applications where extensive machining operations are required and where the improved machinability justifies the slight reduction in corrosion resistance and weldability. It is ideal for automatic screw machine products, fasteners, and precision turned parts.
Key considerations:
- Optimal machinability when cold drawn, but solution-annealed condition is most common for plate/coil.
- Not recommended for marine or highly corrosive chloride environments; use 316 or 316L instead if pitting is a concern.
- Welding should be avoided due to hot cracking risk; if joining is necessary, use AWS E312 filler and minimized heat input.
- Typical applications require no post-machining heat treatment; parts may be used in the as-machined condition.
Product Applications: Screw machine products, Turned parts, Threaded fasteners (nuts, bolts, studs), Valve stems and bodies (for non-corrosive fluids), Shafts and spindles, Bushings and sleeves, Electronic connectors, Fittings and nozzles
Processed into products: Carburetor parts, Injector valve components, Hydraulic fittings, Pneumatic cylinder parts, Dental and surgical instrument handles, Appliance hinges and brackets, Fastener threads and machine screws
Application industries: Automotive (fuel injection components, sensors, bushings), Fastener manufacturing (bolts, nuts, screws, threaded rods), Electronic hardware (terminals, connectors, spacers), Food processing equipment (non-critical parts such as fittings, valves, nozzles), Medical instruments (forceps, handles, dental instruments where minor rusting is tolerable), Aerospace (non-structural turned parts, clevis pins)
JIS G4304/G4305 SUS303 Free Similar / Alternative Materials Recommendation
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| Japan | JIS G4304/G4305 | SUS304 | Identical Cr-Ni base but without intentional S addition; superior corrosion resistance and weldability, but significantly lower machinability |
| USA | ASTM A240 | 304 (UNS S30400) | Counterpart to SUS304; not free-machining |
| Europe | EN 10088-2 | 1.4301 (X5CrNi18-10) | 302/304 equivalent; for better weldability and corrosion resistance where machining is not critical |
| Global | Various | 303Se (UNS S30323) / 1.4300 | Alternative free-machining grade with selenium instead of sulfur; slightly better surface finish and used when sulfur is undesirable but machining still needed |
| Global | Various | 416 (UNS S41600) | Martensitic free-machining stainless, hardenable by heat treatment, but lower corrosion resistance; only suitable for non-austenitic applications |
Notes:
Heat treatment: Solution anneal at 1010–1120 °C followed by rapid cooling (water or air quench). Stress relief at 250–425 °C if needed, but avoid sensitization range (425–860 °C).
Machinability: Rated at approximately 78 % of free-cutting brass, and about 50 % higher cutting speed than SUS304. Use chip breakers and high-speed steel or carbide tools.
Corrosion resistance: Similar to 304 in mild atmospheres, fresh water, and many chemical environments, but pitting and crevice corrosion resistance is inferior in chloride-containing media.
Non-magnetic: In annealed condition, permeability <1.02. Cold working increases magnetism slightly.
Surface finish: Standard finishes as per JIS G4305: No.2B (bright annealed), No.2D, etc. Post-polishing is possible but the sulfide stringers may yield a slightly hazy finish compared to 304.
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