303 vs. 304 stainless steel: what’s the difference?
Austenitic stainless steels vary in their elemental and chemical composition. This stainless steel type shares many of the same characteristics, but their individual properties set them apart from each other. We've put together this guide to help you understand not only how these two grades are similar, but also their main difference. We'll cover:
What is 303 stainless steel?
303 is an austenitic stainless steel grade known for its excellent machinability, attributed to its sulfur content, which ranges between 0.15% and 0.35%. It contains 18% chromium and 8% to 10% nickel. Although these elements usually provide good corrosion resistance, the sulfur significantly reduces this property, along with a slight decrease in toughness.
This tradeoff makes 303 stainless steel easier to machine, as it doesn't require heavy work to form and press. Consequently, it can often be more cost-effective than alloy 304 in machining applications. While 303 is less corrosion-resistant than 304, it still offers good resistance to oxidation when intermittently exposed to temperatures up to 1400°F.
However, the sulfur content negatively impacts 303's weldability, making it prone to cracking. In some cases, selenium is used instead of sulfur, achieving similar effects: improved machinability and reduced corrosion resistance.
Understanding stainless-steel grades.
What is 303 stainless steel used for?
Due to its specific characteristics, 303 stainless steel is not suitable for highly corrosive environments. For such conditions, grades like 304 and 316, which offer superior corrosion resistance, are better options.
303 stainless steel is not considered food grade because it is susceptible to sensitization. Sensitization occurs when the stainless steel is heated to temperatures between 842°F and 1472°F (450°C and 800°C) for extended periods. During this process, chromium carbides form at the grain boundaries, preventing the formation of the passive layer that provides corrosion resistance. To mitigate this issue, the exposure time to high temperatures must be minimized.
Despite these limitations, 303 stainless steel can still be used in certain food handling and preparation equipment, but its use is restricted to environments with lower levels of corrosion.
| Industry | Typical applications | Why |
|---|---|---|
| Food preparation equipment | Conveyors, trays, carts & refrigeration units | Easy to clean |
| Aircraft | Shafts, gears, aircraft fittings |
Non-seizing and non-galling properties are ideal for moving parts High machinability for producing complex shapes |
| Fastening components | Screws, nuts, bolts | High machinability – easy to produce intricate shapes |
| Electronic components | Spacers, brackets, venting elements | Non magnetic, high machinability |
| Industrial equipment & machinery | Bushings, forged shafts, valve bodies, valves, valve trim, fittings | High machinability – easy to produce complex shapes with precise tolerances & tight fits |
Examples of 303 stainless steel used in components include:
Vent plugs
Concealed hinge – 303 stainless steel pin
One-piece pull handles
Lobed knob
Threaded index plunger
What is 304 stainless steel?
304 is another austenitic stainless steel grade. It contains a minimum of 18% chromium and 8% – 10.5% nickel with a maximum of 0.08% carbon.
Grade 304 contains no sulfur, so the chromium is able to provide a passive oxide layer on the surface, protecting it from rust and corrosion. Along with nickel, chromium also enhances the steel's toughness and ductility, making it easy to work with, although it lacks grade 303's high machinability.
304 is tougher than 303 alloy, but it still has good ductility. This makes it easy to fabricate. It also contains small traces of manganese and silicon, which add to the material's strength, formability, and weldability. 304 also stands up to high temperatures. These all make 304 highly corrosion resistant.
Like grade 303 alloy, 304 alloy is non-magnetic, as most austenitic stainless steel alloys typically are. 304 is the most common austenitic stainless steel in use.
Find out how 304 compares to other grades in our guides:
What is 304 stainless steel used for?
303 vs. 304 stainless steel uses are often similar. Specifically, 304 is commonly used in these applications:
| Industry | Typical applications | Why |
|---|---|---|
| Food processing equipment | Tanks, pipes & containers | Corrosion resistance, easy to clean |
| Consumer appliances | Sinks, refrigerators, dishwashers | Durability, corrosion resistance, aesthetic appeal |
| Automotive | Exhaust systems, trim & grilles | Corrosion resistance, aesthetic appeal |
| Medical equipment | Surgical instruments, dental instruments & implants | Biocompatibility, corrosion resistance & withstands high-temperature cleaning processes |
| Chemical processing equipment | Reactors, tanks & pipelines | Corrosion resistance, stands up to a range of chemicals |
| Aerospace components | Aircraft structures, engines | High strength-to-weight ratio, corrosion resistant, thermal stability |
Some of the small components made of 304 stainless steel include:
Spring-loaded removable concealed hinges, base material
303 vs. 304 stainless steel properties
Except for melting point, 303 and 304 share the same properties. Why, for example, would their density be the same when they have a slightly different chemical composition? As austenitic stainless steel alloys, their crystal structure is very similar, with the atoms arranged in a regular, repeating pattern. 304 can have a little more chromium, though not always. The addition of sulfur does not affect the crystal structure or the interatomic spacing in any meaningful way. Hence, they share the same density.
303 vs. 304 stainless steel: a comparison
You'll notice some overlap below between the content of the two stainless steel grades. Interestingly, 303 stainless steel contains more carbon, which would ordinarily mean that this grade should be stronger. The added sulfur counteracts that characteristic, which again, is what makes 304 stronger.
Learn more about carbon steel and stainless steel in our guide, What are the differences between carbon steel and stainless steel?
| Element | 303 stainless steel % | 304 stainless steel % |
|---|---|---|
| Carbon | 0.10 | 0.07 |
| Chromium | 17 – 19 | 18.0 – 19.5 |
| Nickel | 8 – 10 | 8.0 – 10.5 |
| Silicon | 1.00 | 1.00 |
| Manganese | 2.00 | 2.00 |
| Phosphorous | 0.045 | 0.045 |
| Sulfur | 0.015 - 0.35 | 0.015 |
| Nitrogen | 0.10 | 0.10 |
| Copper | 1.00 | - |
303 vs. 304 stainless steel strength
By now you understand that the amount of sulfur in 303 stainless steel affects its toughness in order to make it readily machinable. In general, 304 is stronger than 303 stainless steel. 304 stainless steel contains a higher percentage of chromium (18-20%) and nickel (8-10.5%) than 303 stainless steel, which not only gives it superior corrosion resistance, but higher strength.
While 303 stainless steel has slightly higher ultimate tensile strength (UTS) and yield strength than 304 due to the inclusion-forming elements sulfur and selenium, the strength of a material is not solely determined by UTS or yield strength. Other factors, such as hardness, ductility, and toughness, also play a role in determining the strength of a material. In general, 304 has better mechanical properties than 303.
To understand the Rockwell B hardness test, see our guide, What's shore hardness and why should you care?
| Properties | 303 stainless steel | 304 stainless steel |
|---|---|---|
| Ultimate Tensile Strength | 100000 psi | 73200 psi |
| Tensile Yield Strength | 60200 psi | 31200 psi |
| Hardness (Rockwell B) | 96 | 96 |
| Elongation at Break | 40% | 70% |
303 vs. 304 stainless steel appearance
303 and 304 have similar appearances and are often visually indistinguishable. Both alloys have a face-centered cubic crystal structure and a similar surface finish. The result is a shiny, silvery appearance with a slightly reflective surface.
However, there are some subtle differences in appearance. 303's small amounts of sulfur can give it a slightly duller look compared to 304. Additionally, 303 may exhibit visible machining marks due to its sulfur content, whereas 304 typically has a smoother, more uniform surface finish.
303 vs. 304 stainless steel differences
In summary, these are the primary characteristics of both steels:
| Characteristics | 303 stainless steel | 304 stainless steel |
|---|---|---|
| Corrosion resistance | Good in mildly corrosive environments | Excellent |
| Magnetic | No | No |
| Weldability | Low | High |
| Hardens during cold forming | Yes | Yes |
| Formability | Excellent | Very good |
| Precipitation hardening stainless steels | No | No |
| Machinability (annealed) | Excellent | Fair |
| Resistance to elevated temperatures | Limited | High |
| Maximum intermittent service temperature | 1400°F | 1562°F |
Download free CADs and try before you buy
Free CADs are available for most solutions, which you can download. You can also request free samples to make sure you’ve chosen the right product for what you need.
If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.
Whatever your requirements, you can depend on fast dispatch. Request your free samples or download free CADs now.
Questions?
Email us at sales@essentracomponents.com or speak to one of our experts for further information on the ideal solution for your application 800-847-0486.