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Different stainless steel grades are widely used around the globe for different applications. However, the ASTM 304, JIS SUS304, and EN 1.4301 are among the most common designations for austenitic stainless steel. Each designation comes from a separate standards organization. But all three specify stainless steel with almost the same chemical composition and mechanical properties. This frequently causes misunderstanding among buyers, engineers, and procurement staff. The challenge increases when buyers compare material specifications from different countries.
Figure 2: Buyer checklist for ASTM 304, SUS304, and EN 1.4301
Each standard follows its own criteria. These criteria include composition, mechanical properties, tests, and certification. In many cases, these grades may be treated as equivalents. But there are slight differences, which could be critical. Figure 2 presents the key requirements that buyers have to consider while comparing the grades.
Why 304 Has Different Names in Different Standards
Stainless steel is used worldwide. Each country and area has its own material designation. Therefore, a single stainless steel grade can be denoted differently. In other situations, even two nearly identical grades will also have different designations. There are three different organizations known as ASTM, JIS, and EN, which give their own nomenclature for stainless steel grades. Knowledge of such systems can help the buyers, manufacturers, and engineers to match materials.
ASTM naming system
The ASTM specifications are provided by ASTM International. They are popular in both America and other nations. In the ASTM classification system, the stainless steel grades are denoted using three numbers. For example, 321, in which each number represents a particular grade of stainless steel. The same number is responsible for defining its chemical composition and properties.
ASTM 304 is an austenitic stainless steel alloy. It consists of chromium and nickel as the major elements. The ASTM standard provides material specifications for various products. The ASTM standard also covers test methods, dimensions, and inspection of the products. Such products may be found in plates, sheets, pipes, tubes, and bar forms. The ASTM standards concern product specifications. For this reason, a particular 304 grade appears in different ASTM standards.
JIS SUS naming system
Standards from JIS are developed by the Japanese Industrial Standards. These standards are popular in Japan as well as worldwide among Japanese producers. In the JIS system, stainless steel grades have names that start with the letter “SUS”. SUS is an abbreviation of Stainless Use Steel.
The use of the notation SUS304 indicates that the material is stainless steel by the use of the abbreviation “SUS.” The number “304” is the grade code of the steel. SUS304 is the same as the popular 304 grade of stainless steel in Japan. They are commonly treated as equivalent, but specification details can differ.
EN numeric designation system
The method that European standards employ in the classification of stainless steel grades is a little bit different from that of other systems. Each material has a unique number under the EN system. In the case of stainless steel grades, this number always starts with “1” followed by four digits.
For example, ASTM uses the grade designation 304, while EN identifies the comparable grade as “1.4301”.
Figure 3: ASTM 304, SUS304, and EN 1.4301 standards mapped to comparable stainless steel products
Are ASTM 304, SUS304, and EN 1.4301 Exactly the Same?
ASTM 304, SUS304, and EN 1.4301 can be treated as equivalent grades. However, there are certain differences between the specifications. Table 01 compares chemical composition, minimum mechanical properties, product forms, and standard scope. Most composition limits are similar, but some minimum mechanical-property values differ.
Table 01: Chemical Composition and Mechanical Property Comparison of ASTM 304, SUS304, and EN 1.4301
| Property | ASTM 304 | JIS SUS304 | EN 1.4301 |
|---|---|---|---|
| Carbon (C), max | 0.08% | 0.08% | 0.07% |
| Chromium (Cr) | 18.0–20.0% | 18.0–20.0% | 17.5–19.5% |
| Nickel (Ni) | 8.0–10.5% | 8.0–10.5% | 8.0–10.5% |
| Sulfur (S), max | 0.030% | 0.030% | 0.015% |
| Nitrogen (N), max | — | — | 0.11% |
| Tensile Strength, min | 515 MPa | 520 MPa | 500 MPa |
| Elongation, min | 40% | 40% | 45% |
| Yield Strength (0.2%), min | 205 MPa | 205 MPa | 190 MPa |
| Typical Product Forms | Plate, Sheet, Bar, Pipe, Tube | Sheet, Plate, Bar, Pipe, Tube | Sheet, Plate, Strip, Bar, Pipe, Tube |
| Standard Scope | ASTM product standards | JIS material standards | EN material designation and product standards |
| Material Type | Austenitic Stainless Steel | Austenitic Stainless Steel | Austenitic Stainless Steel |
Chemical composition comparison
The chemical composition of ASTM 304, SUS304, and EN 1.4301 grades is almost identical. All the grades are made of chromium-nickel stainless steel alloy. The chemical composition ranges of these grades have a lot in common. However, the range of some elements in EN 1.4301 may be somewhat different from the ranges in ASTM 304 and SUS304. Such differences do not influence the performance of the materials under normal conditions, but might make a difference in terms of fulfilling the specification of the project or regulation. Therefore, one should not treat the materials as identical and should always refer to the chemical composition requirements stated in the standard.
Mechanical property differences
The mechanical properties of ASTM 304, SUS304, and EN 1.4301 are almost the same. Despite being almost alike, the minimum mechanical properties of these materials may differ slightly, as each of the organizations has different testing procedures and requirements. There may also be differences in reporting criteria. Due to these reasons, the values of tensile strength, yield strength, and elongation may not be considered the same. For practical purposes, such differences rarely influence the performance of these materials. However, they must be taken into consideration in case a certain standard is to be followed.
Product form and standard scope differences
Another important difference is the scope of the standard itself. Besides the identification of material grades, ASTM, JIS, and EN go beyond just that. They define standards relating to certain product forms and uses.
For example, ASTM 304 is typically described by the standards of plates, sheets, bars, pipes, tubes, and fittings. In this case, the standard covers manufacturing, testing, inspection, and certification of the stainless steel products. SUS304 is defined by the Japanese Industrial Standards. It is used for different forms of stainless steel products according to Japanese requirements. EN 1.4301 is the European material designation, which is correlated with EN product standards that describe the requirements for stainless steel products.
How Buyers Should Compare Equivalent Grades
Most buyers think that equal grades of stainless steel are always identical. But in reality, this is not true. It is not enough just to compare names. Comparison of standards will help to eliminate potential errors when selecting materials. It will also help to comply with regulations and achieve desired performance. Buyers need to consult the complete standard and all additional documents before approving any material.
Check the standard, not only the grade name
The grade classification is just one element in the specification of the material. The same material grades could be referred to as ASTM 304, SUS304, or EN 1.4301; however, each of them would have its own separate standard. This standard may have individual requirements regarding the material’s composition, testing and surface requirements, etc.
For example, there may be material labeled as “304 stainless steel,” which conforms to one standard but not to another. It is always better to check the entire designation of the standard and not just its grade.
Confirm product form
The shape of the material is as important as the grade of the material itself. Stainless steel may be available in the form of plate, sheet, coil, bar, rod, pipe, tubing, wire, and fitting. Even though the grades are the same, the requirements for the different forms of the materials are different from one another. This means that while a 304 stainless steel plate will have certain requirements, a 304 stainless steel pipe will have other requirements.
Review the MTC before approval
Material test certificates play a very significant role in material verification. Prior to accepting any shipment, buyers need to study the MTC well. Buyers need to match the data with that of the project specifications and purchase order. This will make sure the material satisfies the grade and standard requirements.
Figure 4: Buyer and quality control engineer reviewing an MTC before material approval
RFQ Example for Multi-Standard Orders
Global procurement sometimes involves comparing materials based on different standards. For instance, an RFQ might result in quotations from suppliers basing their offers on either ASTM 304, SUS304, or EN 1.4301. The type of standards is determined by the location of the supplier and how the supplier manufactures its products.
How to write ASTM/JIS/EN alternatives
In case equivalent grades are acceptable, RFQ must clearly specify the preferred grade and also the accepted equivalents. This will make it easy for bidders from different locations to bid with their material.
The RFQ may contain the following statement:
“Material: ASTM 304 stainless steel. Equivalents are SUS304 and EN 1.4301. Acceptance will depend on the review of the chemical composition, mechanical property, and certification document.”
This will provide the bidder with enough range in the choice of material to offer. Moreover, the buyer will be able to confirm if the material being offered meets the requirements of the project. The RFQ must also specify the product standard, dimensions, and testing requirements.
Figure 5: Multi-standard RFQ comparison for equivalent stainless steel grades
When to accept equivalent grades
Equivalent grades may be used in most cases as long as they fulfill the specifications provided for the project. ASTM 304, SUS304, and EN 1.4301 tend to provide almost identical results in these instances.
Before accepting any grade as an equivalent, buyers are advised to consult the material test certificate. They must also verify the technical data sheets and standards. As long as the grade fulfills all the requirements of function and contract, it can be considered equivalent.
When not to accept substitution
Grade substitution cannot be accepted unconditionally. Some applications require strict adherence to a particular standard. For such a project, no other grade can be substituted for that one, even if the composition is very similar to it.
Conclusion
Different stainless steel designation systems are used around the world. However, the ASTM 304, JIS SUS304, and EN 1.4301 are very similar types of stainless steel. They have the same chemical composition and mechanical properties. Yet these standards are different from each other. There may be differences in the chemical composition limits, mechanical properties specifications, and certification procedures. That is why it would be better to not only focus on the grade name itself but also to make comparisons between the full standard, product form, and specification. Moreover, one needs to pay attention to the material test certificate as well. This way, it will help to avoid some mistakes in the procurement process.
FAQ
Are ASTM 304 and SUS304 the same?
They are often treated as equivalent, but buyers should still compare the complete standard, product form, and MTC before approval.
Can EN 1.4301 replace ASTM 304?
It may be acceptable in many projects, but substitution should follow the project specification, certificate review, and written approval process.
What should buyers check on the MTC?
Check heat number, grade, product standard, chemical composition, mechanical properties, dimensions, test results, and supplier information.
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