Chances are you know about 304 stainless steel (ss), which accounts for 50% of all stainless steel in existence.You’ll find it in products such as kitchen appliances to screws and car parts.
Despite its popularity, 304 often gets lumped in with 303 stainless steel during conversation.
While these stainless steel alloys are one number apart, they do have unique attributes that make one more suitable for certain applications than the other.
Let’s do an old-fashioned 303 vs 304 stainless steel properties comparison.
303 Vs. 304 Stainless Steel Properties Comparison
In evaluating 303ss vs. 304ss, we’ll focus on four key factors where there are distinct differences:
- Ease of use
|Type of Metal||Cost||Machinability||Weldability||Durability|
|303 Stainless Steel||High||Very high||Low||Medium-high|
|304 Stainless Steel||Medium-high||Low||Medium||High|
Buying 303 stainless steel generally costs you a bit more than its numerically higher counterpart. For example, you could be facing nearly double the cost per ⅛” round bar.
Why? 303 stainless steel is made for machining. It’s a steel that requires less work to shape, form, or process, but will still stand up to the demands of use.
But that’s not to say that because 304 stainless steel costs less, you’ll be using an inferior material. What 304ss lacks in the fabrication department, it more than makes up for in durability
Work with an OEM vendor to best navigate the constant change of steel prices. You should also examine your project’s needs -- such as aesthetics and longevity -- to determine whether a more expensive metal is a better investment.
2. Ease of Use
Now we start to see some stark differences.
As we mentioned, 303 stainless steel is easier to work with. It’s considered a free-cutting material. Its fabrication-friendly properties are attributed to the addition of sulfur or selenium to its makeup. Both elements give 303ss the best machinability qualities of any austenitic stainless steel.
Unless you’re looking for a challenge, type 304ss requires additional effort to fabricate because its a bit stronger than 303ss. This stainless steel alloy is non-hardenable by heat treatment. It’s also not a free-cutting material and can be a pain to machine.
More than one engineer has labeled it “gummy” and hard on equipment -- you’re not doing your product or your vendor any favors by specifying 304 for machining. But some projects simply require the additional strength provided by 304 stainless steel.
When comparing 303ss vs. 304ss, the tables turn for weldability. While 303 is easier to machine, it’s a pain to weld. The 304 grade, however, is fairly weldable.
Don’t forget that there is an alternate version of 304 -- 304L. Type 304L stainless steel has low carbon content, adding to its weldability. (There’s also a less common 304H variety.)
Stainless steel is naturally corrosion-resistant -- that’s what it’s famous for, right?
Unfortunately, 303 stainless steel corrosion resistance is reduced a bit because its composition is specialized for machinability.
The 304 stainless steel, however, has excellent corrosion resistance properties. But in warm, salty environments (think projects near the ocean or by heavily salted roads) it’s susceptible to pitting.
Still, 304 takes the cake when it comes to durability. got excellent toughness. 304 machinability is less than 303's, but you could say that about any other stainless grade, too.
The 303ss grade’s machinability makes it useful for small, intricate components. You’ll often see it in:
- Nuts and bolts
- Aircraft gears and fittings
Meanwhile, 304ss is a top choice in projects where aesthetics and cleanliness are key. These include:
- Food processing
303ss Vs. 304ss: Different, But Similar
These two stainless steel types are classified under the austenitic series of metals. Austenitic stainless steels are (normally) non-magnetic and have high levels of chromium and nickel content. They’re known for their formability and resistance to corrosion compared with other series and metals.
Both 303 and 304 are iron alloys. Their composition is nearly identical. If you want to take a deeper dive into their specs, check out this handy graph.
(Need a chart of all the relevant stainless steel grades? Look here.)
Know Your Metal Types -- or Ask a Vendor
Concerned about using 304 because it’s hard to machine? Or are you worried about using 303 because it’s less weldable? Get an experienced OEM vendor involved to optimize your design and material selection.
Or maybe you want something that can stand up to salt corrosion or that’s a little cheaper.
Here are a few resources for more guidance on stainless steel grades:
- 304 vs. 316 stainless steel tubing
- 316 vs. 316L stainless steel
- Stainless steel vs. carbon steel tubing
- Cost of stainless steel tubing vs. aluminum tubing
Either way, always know your metal! A little research now saves you lead time and money later.
(Editor's note: This article was originally published in November 2017 and was recently updated.)