303 vs. 304 stainless steel: what’s the difference?
Austenitic stainless steels vary in their elemental and chemical composition. They share 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 with excellent machinability due to its sulphur content which ranges between 0.15% and 0.35%. Its chromium content is 18% and nickel, 8% – 10%. The corrosion resistance this would normally provide is offset by the sulphur content to a large degree. The result is, the resistance to corrosion is lowered, along with a slight decrease in toughness.
That’s the tradeoff for being readily machinable. It doesn’t require heavy work to form and press, which can often make it more expensive than alloy 304. While 303 is less corrosion resistant than 304, it still has good resistance to oxidation when intermittently exposed to temperatures of up to 760°C.
Note, the sulphur content gives 303 poor weldability, which can result in cracking. Also, sometimes selenium is used instead of sulphur. This has the same result of sulphur, improving machinability and lowering corrosion resistance.
You can learn more in our guide, Understanding stainless-steel grades.
What is 303 stainless steel used for?
The characteristics of 303 stainless steel mean that you shouldn’t use it in highly corrosive environments. There are better austenitic stainless steel grades for that purpose, such as 304 and 316.
303 stainless steel is not food grade, as it’s vulnerable to sensitisation. This happens when the stainless steel is heated to temperatures between 450°C and 800°C for an extended period of time. Chromium carbides form at the material’s grain boundaries, which means it can’t form the passive layer that provides corrosion resistance. The way around this is to restrict the amount of time it's exposed to high temperatures.
All of that said, 303 stainless steel can be used in some food handling and preparation equipment, though its applications are limited to lower corrosive environments.
| 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:
Concealed hinge – 303 stainless steel pin
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 sulphur, 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, 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.
Like grade 303, 304 is non-magnetic, as most austenitic stainless steel alloys typically are. 304 is the most common austenitic stainless steel in use.
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:
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 sulphur 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 sulphur counteracts that characteristic, which again, is what makes 304 stronger.
| 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 |
| Sulphur | 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 sulphur 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 sulphur 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 | 690 MPa | 505 MPa |
| Tensile Yield Strength | 415 MPa | 215 MPa |
| 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-centred 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 sulphur can give it a slightly duller look compared to 304. Additionally, 303 may exhibit visible machining marks due to its sulphur 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 | 760°C | 850°C |
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