SS Vs. SUS … Is There a Difference? Yes and No

Scientists and engineers have a habit of giving weird names to things, or at least struggling to align them universally. 

Acronyms and abbreviations lend themselves to being not exactly reader friendly. 

Abbreviations for stainless steel are no different. A common question we see on metalworking forums is “SS vs. SUS: What the heck is the difference?”

If you don’t know the answer, don’t feel bad -- it’s not exactly an easy question. And the answer is a little ambiguous. 

Let’s dissect what makes these two stainless steel designations the same -- and different.z

SS Vs. SUS: What Do They Mean?

As you may have guessed, “SS” is the abbreviation for “stainless steel.” It’s the American way of listing steel grades (ex: SS grade 316).

“SUS,” on the other hand, is the typical Japanese Industrial Standards (JIS) designation for stainless steel grades. It stands for “steel use stainless.”

Despite the difference of one letter in these stainless steel abbreviations, American and Japanese steel grades still line up identically. 

For instance, let’s say you need to order 316 grade stainless steel -- one of the strongest and most corrosion-resistant metals on the market. If you were to put “SS 316” and “SUS 316” on your order form, you’d be specifying the same metal twice. You’d end up getting that same versatile alloy of chromium and nickel.

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."

RELATED: The 12 Cons of Offshoring (free download)

To recap: SS and SUS are the same thing.

However ...

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). To continue with using 316 stainless steel as an example, notice there 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 steel is corrosion resistance. Yet, in this example, the differences in its chemistry -- which are directly attributed to the region it’s sourced from --  affect the grade’s ability to fight corrosion in many applications. In other words, a small difference in a metal’s chemical composition can have a big impact on the longevity or functionality of a finished product. 

As simple as it may sound, always ask your manufacturer if the differences in the metal grade of choice are enough to impact your component’s performance.

Other Metal Industry Acronyms to Know

The standards organization SAE International maintains several alloy numbering systems. One of which 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), that are also used. If you run into a steel grade numbered like this -- “S31600” for 316 stainless steel, for example -- you’ve seen a UNS designation. 

And there are other standards used elsewhere in the world (but you’re not really risking offshoring your manufacturing, are you!?), including:

• British Standards (BS)
• German (DIN)
• Chinese (GB)

Don’t worry -- few vendors will expect you to speak their language and its many deviations fluently. 

Navigating Stainless Steel Abbreviations

While we may be a little biased, there three solutions we recommend to avoid any issues  when specifying a choice of metal:

1. Work with an all-in-one vendor: A full-service vendors are used to procuring raw materials and know all the tricks of the metal numbering and designation systems so you don’t have to. 
2. Buy your products from the United States: Sticking with USA-based products means you won’t have to worry about using a foreign abbreviation. And as an added bonus, there won’t be any geographic impacts on your metal’s chemistry that could cause issues later. 
3. Spell it out: Put simply,  “stainless steel” can’t be misunderstood; “SUS” can.

We mentioned working with an all-in-one OEM vendor. 

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(Editor's note: This article was originally published in September 2017 and was recently updated.)