Scientists and engineers have a habit of giving weird names to things, or at least struggling to align them universally. Stainless steel is no different. A common question we see on metalworking forums is “SS vs. SUS: What’s the difference?”
Don’t feel bad for not knowing the answer. But do pay attention to what makes these two stainless steel designations the same -- and different.
SS Vs. SUS: What Do They Mean?
SS, as you may have guessed, stands for “stainless steel.” It’s the American way of listing steel grades (ex: SS grade 316).
SUS is the typical Japanese Industrial Standards (JIS) designation for stainless grades. American and Japanese steel grades line up identically. By ordering both SS 316 and SUS 316, you’re basically specifying the same metal twice. It’s still that same, lovable alloy of chromium and nickel.
(Fun Fact: SUS stands for "steel use stainless.")
Actually, despite many different systems existing globally, most of them use the same numbers for the common grades, like 316 and 304. That said, if you use the term "SUS," you risk your vendor failing to understand what you’re looking for. It’s better to just say "stainless steel."
If you’re looking for a chart of the most common grades of stainless steel (listed by names you’ll actually recognize), click here.
To recap: SS and SUS are the same thing.
Why You Should Beware SUS
While the stainless steel grade numbers are usually the same from country to country, it’s rare to find identical chemical compositions.
The table above shows comparative austenitic stainless steels from the United States, Japan, and European Union (in that order -- note the ASTM, JIS/SUS, and EN designations). In this example of 316 stainless, here are differences in the chromium, nickel, and molybdenum contents among all the standards and a different nitrogen limit in the European Union (EN) standard.
The main benefit of 316 stainless is corrosion protection. Yet, in this example, the differences in content can affect the grade’s ability to fight corrosion in many applications. Always ask your manufacturer if the differences in the metal grade of choice are enough to impact your component’s performance.
Other Acronyms to Know
The standards organization SAE International maintains several alloy numbering systems, one of which, for steel grades, is the SAE steel grades system.
In the 1930s and 1940s, the American Iron and Steel Institute (AISI) and SAE were involved in similar, overlapping efforts to standardize a numbering system. For decades, the systems were merged into a joint system -- the AISI/SAE steel grades. AISI handed over future maintenance of this system to SAE in 1995.
We bring this up because some of today’s steel quotes and certifications still reference both SAE and AISI.
There are other alloy numbering systems, such as the ASTM-SAE unified numbering system (UNS), though few vendor will expect you to speak this language. If you run into a steel grade numbered like this -- “S31600” for 316 stainless steel, for example -- you’ve seen a UNS designation.
Lost yet? There are other standards used elsewhere in the world, including:
- British Standards (BS)
- German (DIN)
- Chinese (GB)
(But you’re not really risking offshoring your manufacturing, are you!?)
We’re biased, but these two solutions make total sense when specifying a choice of metal:
- Work with an all-in-one vendor
- Buy your products from the United States
- Spell it out
Working with a vendor that’s used to procuring raw materials will know all the tricks of the metal numbering and designation systems. And you’ll avoid confusion and discrepancies in material traits if you stick with USA-based products. Finally, just spell it out for your vendor -- “stainless steel” can’t be misunderstood; “SUS” can.