Many know 316 stainless steel as the go-to metal for heavy-duty applications. It’s tough, corrosion-resistant, and … expensive.
An astounding 9 out of 10 manufacturers agree 316 is the best stainless steel grade for corrosion resistance. (Disclaimer: We made up that survey.) Do you need 316 stainless steel's corrosion resistance for your part, or can you skate by with a cheaper product? It depends on your application.
To give you an idea of how 316’s protective properties (and price) compare, let’s put it up against other metals as well as other types of stainless steel.
Many consider type 316 stainless to be the ultimate grade in corrosion protection. That’s why some call it “marine grade” -- it can even withstand consistent saltwater immersion and splashing.
Its viability in marine environments is also what makes it one of the most expensive materials out there. Let’s compare some of the most notable ones:
There’s a type 316 variant called 316L stainless steel. Performance-wise, 316L is better than any other stainless steel for extreme-temperature, high-corrosion applications. Yes, even better than its cousin, though the margin’s slight. It’s widely popular for construction and infrastructure jobs.
(Don’t forget there’s another simple-but-notable difference between 316 and 316L stainless.)
The added chromium in stainless steel makes it more corrosion resistant than carbon steels. Although if you’re considering ugly, ol’ carbon steel in the first place, you may not care if your part looks like vomit. The rough surface that rusting leaves, however, may be another story.
Carbon steel is far cheaper than stainless steel, so weigh that against your need for protection.
(Related Chart: Click here for a chart of carbon steel grades, including their characteristics and best uses.)
For some cost-conscious engineers and buyers, galvanized carbon steel is the most economical process for protecting a part from corrosion. Its zinc coating is an on-the-cheap way to imitate stainless steel. It can actually outperform many stainless steels in salty environments because the zinc layer prevents the carbon from reacting with chloride.
Aluminum has high oxidation and corrosion resistance thanks to its passivation layer. This is a naturally occurring, self-protective layer. When aluminum oxidizes, its surface will turn white and sometimes pit.
In some extremely acidic or base environments, aluminum may corrode in a hurry, leaving you with a mess.
On the plus side, aluminum is almost always cheaper than stainless steel.
(Related Chart: Aluminum Grades in PDF Form)
All stainless steel is naturally corrosion-resistant -- that’s what it’s famous for, right? But even stainless steel can corrode if the wrong grade is used in the wrong place.
In numerical order, here are the most common ones that specialize in fighting corrosion:
This metal gets its weird name in part because it has high chromium content. It's low-cost and is basically the mutant child of 409 stainless (which you'll see below).
3CR12 resists mild corrosion, particularly in wet abrasion environments. It’s common in:
301’s corrosion resistance is notable, though not as strong as 304’s. It's well suited for forming, welding, and drawing.
This grade has uses in:
Type 302 stainless boasts corrosion resistance comparable to grade 301. Notably, it's non-hardenable and extremely ductile.
It’s great for applications such as:
Then there's 304 stainless steel, without a doubt the world's most popular grade of stainless steel. In terms of 304 vs. 316, you're getting a tradeoff of pros and cons.
Type 304 makes up about 50% of all stainless produced, so it’s readily available. The price is lower than 316’s and is often the basis for comparing the prices of other grades.
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.
Applications include:
Worried about oxidation? 309S stainless steel is resistant to it. It’s also more resistant than 304 to temperature changes. It’s used in heating and furnace parts, as well as other elevated-temperature applications.
The 317 grade actually offers better wear resistance than 316. Please note the difference between wear and corrosion resistance. Wear resistance means durability against abrasions, impacts, and so on.
Type 317 is going to cost you a few more bucks for that protection. It’s useful for:
The 409 grade resists atmospheric and automotive exhaust corrosion. Notably, it’s about as cheap as stainless steel gets. The aluminized version of 409 adds salt and cosmetic wear resistance. Uses of these grades include:
Type 430 balances good corrosion resistance with other qualities. (Warning: The 430F variation is inferior in wear protection.)
It’s far cheaper than 304 ($0.94/lb. vs. $1.63/lb., the last we checked) due to lower nickel content. Common applications include:
If you want better pitting resistance than what you get from 430, try 434 and its added molybdenum. The price of 434 is also lower than 304’s.
One common application for 434 stainless steel is automotive trim and molding.
Type 440 ups the chromium and carbon even more to improve toughness, abrasion resistance, and corrosion resistance. There are four versions of this grade: 440A, 440B, 440C, and 440F. The difference between the four is the amount of carbon inside.
Typical applications include instruments. It's also known as "razor blade steel" for reasons you can probably figure out.
(Related Chart: Stainless Steel Grades in PDF Form)
There are loads of stainless steel grades that are lesser known. Click here for a more exhaustive list of grades, including their traits and ideal uses.
The metal on your mind not on this list? That’s probably for one of two reasons:
Availability matters -- grades that manufacturers don’t use often may take extra time and money to obtain. Remember that if you opt for a stainless steel alloy that's cheaper than 316.
For more on metal manufacturing materials, check out these related articles. Or, we suggest you check out the free e-book below -- it's all about applying the best finish for your product, whether it's with durability or aesthetics in mind.
(Editor's note: This article was originally published in December 2017 and was recently updated.)