Chances are you know about 304 stainless steel, which accounts for 50% of all stainless steel in existence. Despite its superior popularity, 304 often gets lumped in with 303 stainless steel during conversation.
Why? Beats us. They’re one number apart, but they do have noticeable differences that make one more suitable for certain projects than the other.
Let’s compare the two.
303 Vs. 304 Stainless Steel: Similarities
These two grades fall under the austenitic series of metals. Austenitic steels are (normally) non-magnetic and high levels of chromium and nickel. 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 a more exhaustive set of specs, try this handy graph.
(Need a chart of all the relevant stainless steel grades? Look here.)
303 Vs. 304 Stainless Steel: Differences
Buying 303 stainless steel can cost you a bit more than its 304 counterpart. For example, you could be facing nearly double the cost per ⅛-inch round bar.
Work with an OEM vendor to best navigate the constant change of steel prices. You should also examine your project’s needs -- aesthetics and durability, for example -- to determine whether a more expensive metal is worth it.
2. Ease of Use
Here’s where 303 and 304 stainless steel really stand apart.
First, the machinability factor. Type 303 is a free-cutting material. The addition of sulfur or selenium to its makeup gives it the best machinability of any austenitic stainless steel.
Type 304 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 303 for machining.
The flipside of this is weldability. Type 303 gets mad when you try to weld it. The 304 grade, however, is fairly weldable.
Don’t forget that there is an alternate version of 304 called 304L. This version 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, type 303’s specialization in machinability comes at the cost of lower corrosion protection.
The 304 grade has wonderful corrosion resistance, but it’s susceptible to pitting in warm chloride environments. (Think projects near the coast or heavily salted roads.) Still, it’s got excellent toughness.
4. Best Applications for Each
The 303 grade’s machinability makes it useful for small, intricate components. You’ll often see it in:
- Nuts and bolts
- Aircraft gears and fittings
Meanwhile, 304 is hugely popular in projects where aesthetics and cleanliness are key. These include:
- Food processing
Know Your Metal Type -- or Ask a Vendor
Concerned about using 304 because it’s hard to machine or using 303 because it’s less weldable? Get an experienced OEM vendor involved to optimize your design and material use.
Or maybe you want something that can stand up to salt corrosion or that’s a little cheaper. These resources can guide you to the right metal:
- 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.