Updated on February 25, 2025.
Steel is a complex engineered material that comes in almost an infinite variety of chemistries and designations, each tailored to a specific application. Aside from the selection process, steel material science is complicated enough, even for a seasoned engineer.
There are multiple international standards with their own unique designators for the steel chemistries and mechanical properties, including JIS and AISI standards. This article provides an understanding of how these two standards match up against each other.
Disclaimers
It’s important to note that two exactly equivalent steel specifications do not exist. Even if two comparable steel specifications across different standards possess the same mechanical properties and/or the same chemical composition, the steels manufactured to these two standards may not be exactly equivalent.
With the two standards being maintained by two separate organizations, it’s possible they may diverge in the future or have diverged at some minor inflection in the past. The fact is that finely tuned nuances may exist in the chemical compositions and processing techniques that make two identical steels across standards impossible.
AISI/SAE and UNS Designation Definitions
The American Iron and Steel Institute (AISI) is a trade association consisting mainly of North American steel manufacturers. This organization, originally chartered in the US, traces its roots back to the middle of the 19th century, staking claim to the title of one of the first trade associations.
One of the ways that it accomplishes its primary mission of advancing the steel industry is through the creation and maintenance of a common set of standards, which are today maintained by the Society of Automotive Engineers (SAE).
The Unified Numbering System (UNS) steel standards are very similar to the AISI standards because they are simply a renumbering of the underlying AISI standards.
The only minor differences between the two standards are the fact that the UNS standard typically possesses an extra letter in front of the specification (e.g., “S” for “Steel”) and a few extra digits of identifying information at the end of the specification. This is apparent by examining the expansive table shown at the end of this discussion.
AISI Carbon and Alloy Steels
For carbon and other common alloy steels, the naming convention is actually intuitive to understand, and it’s based on a simple four-digit numbering system, where the first digit tells you the classification of the steel.
For example, 1XXX is reserved for carbon steels, while 9XXX is reserved for silicon manganese steels. Next, the final two digits in the specification denote the alloy weight % of carbon in “hundredths” of a percent.
In this way, it’s possible to know a bit about the composition of the steel, simply from its name. For example, 1040 AISI steel is carbon alloy steel that contains 0.40 weigh t% carbon alloy. The full breakdown of this table is shown below.
| AISI/SAE Designation-Generic | Type |
| 1XXX | Carbon steels |
| 2XXX | Nickel steels |
| 3XXX | Nickel-chromium steels |
| 4XXX | Molybdenum steels |
| 5XXX | Chromium steels |
| 6XXX | Chromium-vanadium steels |
| 7XXX | Tungsten steels |
| 8XXX | Nickel-chromium-molybdenum steels |
| 9XXX | Silicon-manganese steels |
Stainless Steels and High Strength/Low Alloy Steels
For stainless steels, the designation is shorted slightly to a 3-digit number, but the same general rule applies: there are 100, 200, 300, etc., up to 900 stainless steel series levels depending on the main alloying ingredient and iron phase.
For example, 300-series stainless steels are austenitic and alloyed with chromium, while 400-series stainless steels are ferrous, martensitic, and also contain chromium as an alloying element.
However, there is a slight difference here in how stainless steels are numbered in the UNS/AISI standard, as they are simply numbered in a somewhat sequential fashion such that the chemistry of 301 stainless steel is entirely different from 304 stainless steel.
JIS Standards
On the opposite side of the Pacific, the Japanese Industrial Standards (JIS). These standards are maintained by the Japanese Industrial Standard Committee and set the standard for all industrial activities in Japan.
JIS standards are denoted as follows: “JIS X 0208:1997,” where X is a division letter (A-Z) represents the specific area division, followed by a four-digit identification number. Sometimes there are 5 digits cited when the JIS standard directly references a corresponding International Standards Organization (ISO) standard. Finally, the last four digits are the revision release year.
The industrial disciplines covered by these standards are incredibly expansive. JIS standards exist for an amazing breadth of topics from ceramics to aviation. For the purposes of this discussion, the steel specifications are found in the G standard.
However, it’s not too difficult to link the AISI standards to JIS specifications; since the JIS specs postdate the AISI standards, the JIS specs pretty much follow along in the path that the AISI standards blazed, with the exception being that the numbers in the JIS specs are sequentially numbered and typically contain any information about the steel chemistry.
The JIS number roughly follows the AISI format wherever possible. For example, SUS 304 is equivalent to AISI 304.
Note also that the JIS standards for steel also contain a three-letter identifier in front of the specification; for example, stainless steels are denoted as SUS XXX while tool steels are designated as either SKH/SKD/SKS XXX, etc.
Additionally, special-purpose steels such as chromium or silicon steels, which would be the AISI 5000/6000/9000 series steels, are generally designated as SUP/SUJ/SUM in the JIS specification.
VIEW COMPARISON OF MATERIAL JIS AND RELATED OVERSEAS STANDARDS
Although steel specifications might be comparable, they should never be assumed to be equivalent, especially for new steel chemistries such as high-speed tool steels like AISI T4/T5.
It is only after a careful study of the chemical composition of the steel and processing parameters across both standards that an assessment of equivalence can really be made.
These nuances exist for every steel grade across all international standards, and the differences are waiting to be discovered!
