You may already know the most common stainless steel grades in manufacturing: 304 and 316. But what’s behind their popularity? The success of your stainless steel tubing project may depend on you knowing the difference.
If your top concern is your component’s cost or weight, you may want to compare stainless with carbon steel tubing or aluminum tubing. If you’re full-go on stainless, then read up on its two most popular grades:
What's 304 Stainless Steel Tubing? What's 316?
First, let’s look at their composition. The 304 grade contains:
- 18% chromium
- 8% nickel
Meanwhile, 316 stainless contains:
- 16% chromium
- 10% nickel
- 2% molybdenum
Type 304, due to its chromium-nickel ratio and low carbon level, is the most widely used of the austenitic stainless steels.
How 304, 316 Stainless Steel Tubing Are Alike
Both 304 and 316 stainless (as well as other 300-series stainless grades) use nickel to keep an austenitic composition at lower temperatures. Austenitic steels allow for a balance of strength, corrosion protection, and workability.
There’s a lot to like about both grades of tubing. They’re particularly easy to:
- Clean and sanitize
304 Vs. 316: The Differences
Grade 304 is the lowest-cost corrosion-resistant option in the world of stainless steel. The higher nickel content and use of molybdenum make grade 316 stainless a tad more expensive per ounce of material.
Type 316 costs more initially, but it can save you money in the long run -- especially if your part will reside in the harsh outdoors.
Type 304 boasts solid resistance to oxidizing acids and corrosion. This stainless grade does have a weakness, though: It’s susceptible to corrosion on the coast and near heavily salted roads. Chloride can create localized corrosion called pitting, which can spread beneath protective barriers and compromise your component.
Where 304 stainless falters, 316 offers superior corrosion protection thanks to the presence of molybdenum. It’s chloride-resistant, so it’ll stay strong in saline-heavy environments. There’s a reason manufacturers call it “marine-grade stainless.”
Stainless steels with molybdenum are also a must for certain pharmaceuticals to avoid metallic contamination.
3. Ease of Use
In terms of formability, grade 304 is the superior option. A combination of lower strength and lower work hardening rate make 304 easier to deal with. While your vendor can work with 316 similarly, temperature variation can affect the ease of these processes.
(Fun Fact: Cold working can cause 316 stainless steel to become magnetic.)
Note that 304 steel is a bit less weldable than 316. Your manufacturer should watch out for hot cracking and loss of corrosion resistance. With the 316 grade, weld difficulty is not an issue whatsoever.
Since we’re talking ease of use, we must mention 316 stainless steel tubing is not readily available in as many sizes, forms, and finishes as 304 tubing. This means 304 gives you a bit more versatility.
Know Your Materials
Settling on a number doesn’t mean your work is done. There are multiple takes on both 304 and 316 stainless steel tubing. For example, do you know the simple difference between 316 and 316L stainless steel? So be diligent, and -- even better -- get an all-in-one manufacturer involved so you get your project right the first time.