303 Stainless Steel Plate - UNS S30300 - ASTM-A-895
303 stainless steel is a free machining modification of the basic 18-8 stainless steel. This austenitic, nickel stainless steel was specially designed for improved machinability while maintaining good corrosion resistance. It is used primarily for parts requiring machining, grinding or polishing. The sulfur addition present in 303 SS assists in breaking up turnings which reduces drag on cutting tools. This alloy offers good corrosion resistance and oxidation resistance in mild environments and excellent forming properties. It is non-magnetic in the annealed condition and is not hardenable by heat treatment – it can only be work hardened through cold working. It is also difficult to weld, and may require filler rods and post-weld annealing to maintain corrosion resistance.
- Inventory & Specs
- Chemical Composition
- Physical Properties
- Mechanical Properties
- Datasheet
- Additional Info
- FAQs
Inventory Size Ranges for 303
| Type | Thickness | AMS Standards | ASTM | UNS | Get a Quote |
|---|---|---|---|---|---|
| Plate | 0.1875" - 4.000" | AMS 5640 (Chem Only) | ASTM A 895 | UNS S30300 | Get a Quote |
Characteristics of 303 stainless steel
The improved machinability of 303 stainless steel alloy (UNS S30300) makes it ideal for screw machine applications, aircraft fittings, and fasteners. The additional sulfur that allows this material to be readily machined also lowers its corrosion resistance compared to a grade like 304 stainless steel. Overall toughness is lower but still good, despite the inclusion of sulfur, and is comparable to other austenitic grades of stainless steel. 303 alloy has good resistance to oxidation at temperatures up to 1700°F (927°C). In extreme oxidizing atmospheres, irregular scaling may be encountered, particularly above 1400°F (760°C).
Working with 303
For maximum ductility, 303 alloy should be annealed near the upper limit of the 1800 - 2000°F (982 - 1043°C) range. The material should be water quenched from the annealing temperature to prevent harmful carbide precipitation. For the same reason, heating within the 800 - 1500°F (427 - 816°C) temperature range should be avoided unless the material can be subsequently annealed. 303 alloy is austenitic and cannot be hardened by heat treatment. High machining rates can be obtained for this material in the annealed condition, with hardness in the range of 200 to 240 Brinell. However, modifications in machining techniques are necessary to adjust to the special characteristics of 303 stainless steel. Since 303 alloy will work harden, it should be machined at reduced surface feet per minute and heavier feeds to prevent glazing at the tool interface. Although the free machining grades are not recommended for welding, they may be welded with some difficulty. 303 alloy may be welded with Type 310 electrodes and should be annealed after welding to redissolve precipitated carbides, thereby increasing the resistance of the material to intergranular corrosion.
Other industry standards we comply with:
Common Trade Names
- AISI 303
Industry Applications for 303
- Aircraft applications including fittings, shafts and spindles
- Automatic screw machine applications
- Medical devices with screw threads, drilled or tapped holes
- Pump and valve parts
- Architectural applications
- Nuts and bolts
Chemical Composition
| Element | Min | Max | |
|---|---|---|---|
| Cr | Chromium | 17.0 | 19.0 |
| Ni | Nickel | 8.0 | 10.0 |
| C | Carbon | 0.15 | - |
| Mn | Manganese | 2.00 | - |
| P | Phosphorus | - | 0.20 |
| S | Sulfur | 0.15 | 0.35 |
| Si | Silicon | - | 1.00 |
| Mo | Molybdenum | - | 0.60 |
| Fe | Iron | - | Balance |
Physical Properties
| Property | Value |
|---|---|
Density lb/in3 | 0.289 |
Density g/cm3 | 7.89 |
Melting Point | 2552°F |
Thermal Conductivity at 212°F (100°C) | 112 BTU/hr/ft²/ft/°F |
Thermal Conductivity at 212°F (100°C) | 16.2 W/m-°K |
Electrical Resistivity | 28.3 Microhm-in at 68°C |
Electrical Resistivity | 72.0 Microhm-cm at 20°C |
Mechanical Properties
| Property | Value |
|---|---|
Hardness | Max 202 (HBN) |
Datasheet
Additional Info
A Brief History of 303
303 stainless steel belongs to the 300‑series austenitic stainless steels, which include well‑known grades like 302, 304, and 316. It was introduced as part of the industry’s effort to create easier‑to‑machine stainless alloys while preserving the corrosion resistance that made 18‑8 steels popular. The key innovation was the addition of sulfur or selenium, which dramatically improved machinability compared to standard 304 stainless steel.
How 303 Was Developed
Engineers were looking for a stainless alloy that could be cut, drilled, and milled more efficiently than 304, which tends to work-harden and wear tools down. The solution was to modify 18-8 composition by adding controlled amounts of sulfur, which acted as a chip-breaker, improving machinability. The addition of sulfur also reduced friction on cutting tools. This development produced a stainless steel that maintained the chromium and nickel levels of 304 but offered far better machinability.
Early Applications of 303
Early uses centered on industries that needed high-volume machining of corrosion resistant parts, such as fasteners, fittings, couplings, shafts, small precision components, switchgears, electrical hardware, and valve parts. These applications leveraged 303's ability to be machined quickly and consistently without excessive tool wear.
How 303 is Used Today
303 remains one of the most machinable stainless steel alloys available, and it is widely used for precision-machined components in the aerospace, automotive, and industrial industries. Some common applications include gears, screws, bolts, hydraulic and pneumatic fittings, medical and dental instruments, kitchen equipment, and appliances.
Your Trusted Supplier for 303 Stainless
United Performance Metals carries 303 stainless steel plate 0.1875" - 4.000". This product is used for aerospace applications including fittings, shafts, and spindles, medical applications including med devices, screw threads, drill and tap holes, as well as fasteners and architectural applications.
Product FAQs
303 stainless steel offers good strength and excellent machinability. 303 is non-magnetic in the annealed condition but may become slightly magnetic after cold work.
Yes, 303 is much easier to machine compared to other stainless steel grades due to its high sulfur content which improves chip-breaking and reduces tool wear.
303 is most commonly used for fittings, fasteners, precision machined parts, and gears. 303 is not typically recommended for food-grade applications due to its sulfur content which reduces the alloys' corrosion resistance.