SUS304 vs. SS304 Stainless Steel: What’s the Difference?
Introduction
304 stainless steel is one of the most widely used austenitic stainless steels in the world, known for its excellent corrosion resistance, formability, and versatility across industries. However, depending on the region, it may go by different names—most notably SUS304 in Japan and SS304 in the United States.
This difference in naming conventions often leads to confusion. Some may even wonder if SUS304 and SS304 are different materials, or if they exhibit mechanical differences that affect performance.
This article aims to clarify the technical and practical differences between SUS304 and SS304. By comparing their definitions, compositions, mechanical properties, and use cases, we provide a clear answer to whether they can be treated as equivalent—and under what conditions.
What Is SUS304 Stainless Steel?
SUS304 is a stainless steel grade defined under the Japanese Industrial Standards (JIS). The “SUS” prefix stands for “Steel Use Stainless,” and SUS304 is essentially the Japanese version of AISI 304. It is categorized as an austenitic stainless steel and features a composition of approximately 18% chromium and 8% nickel, which gives it strong resistance to oxidation and corrosion.
SUS304 is widely used across Asia, especially in Japan, for products that require durability and hygiene. These include:
- Food processing equipment
- Kitchen sinks and utensils
- Building facades and structural components
- Chemical containers and tanks
It performs reliably under ambient conditions and retains mechanical strength in both high- and low-temperature environments. Due to its excellent cold workability, weldability, and mechanical properties, SUS304 is often selected for both industrial and consumer applications in Asian markets.
What Is SS304 Stainless Steel?
SS304 is the stainless steel grade as defined by the American Iron and Steel Institute (AISI) and is regulated under ASTM standards, most notably ASTM A240. Like SUS304, SS304 is an 18/8 austenitic stainless steel, composed of roughly 18% chromium and 8% nickel.
SS304 is considered the default stainless steel grade in North America and Europe, widely available in annealed or cold-worked conditions. It offers:
- Excellent corrosion resistance in mild environments
- Good formability for stamping, bending, and machining
- Strong weldability, making it ideal for fabricated structures
Common applications include:
- Medical and pharmaceutical equipment
- Food and beverage processing tools
- Architectural finishes
- Household appliances
SS304 is frequently the baseline material against which other stainless steel grades are compared, particularly due to its balance of performance and cost.
SUS304 vs SS304: Chemical Composition Comparison
Despite being specified under different standards, the chemical composition of SUS304 and SS304 is virtually identical. Both belong to the same 18/8 family of stainless steels and share the same primary alloying elements.
| Element | SUS304 (JIS G4303) | SS304 (ASTM A240) |
|---|---|---|
| Carbon (C) | ≤ 0.08% | ≤ 0.08% |
| Chromium (Cr) | 18.0–20.0% | 18.0–20.0% |
| Nickel (Ni) | 8.0–10.5% | 8.0–10.5% |
| Manganese (Mn) | ≤ 2.0% | ≤ 2.0% |
| Silicon (Si) | ≤ 1.0% | ≤ 1.0% |
| Phosphorus (P) | ≤ 0.045% | ≤ 0.045% |
| Sulfur (S) | ≤ 0.03% | ≤ 0.03% |
Any differences are negligible and generally arise from regional tolerances rather than intended mechanical distinctions. The two grades are also equivalent to European standard EN 1.4301 and German X5CrNi18-10, which are often cited in global supply chains.
Mechanical Properties Comparison
When it comes to mechanical performance, both SUS304 and SS304 behave nearly identically under standard testing conditions. Their austenitic microstructure provides high toughness, making them suitable for both structural and aesthetic applications.
| Property | Typical Value (Both SUS304 & SS304) |
|---|---|
| Tensile Strength | 515 – 750 MPa |
| Yield Strength | ≥ 205 MPa |
| Elongation (in 50mm) | ≥ 40% |
| Hardness (HRB) | ≤ 92 (annealed) |
| Corrosion Resistance | Excellent in oxidizing environments |
| Weldability | Excellent |
| Formability (Cold Working) | Good |
Both grades are non-magnetic in the annealed condition, although slight magnetism can develop after cold working. Their excellent corrosion resistance, ductility, and formability make them versatile for complex manufacturing processes like deep drawing, bending, and spot welding.
In terms of weldability, SUS304 and SS304 perform exceptionally well with various welding techniques such as TIG, MIG, and arc welding. Their high nickel content reduces the risk of brittleness in the heat-affected zone, ensuring post-weld mechanical strength is retained. Some minor regional preferences may exist—for example, argon arc welding is more commonly optimized for SUS304 in Japanese applications—but both grades remain highly reliable across global welding scenarios.
Regarding machinability, the two grades are nearly indistinguishable under standard shop conditions. However, slight differences may arise due to tooling, cooling methods, or regional manufacturing practices. For critical applications, pre-production testing or adjustments in cutting speed and tool selection can help achieve optimal results and prolong tool life.
Finally, cost considerations are not due to the material itself but are shaped by geographic sourcing. SUS304 is more prevalent and often more cost-efficient in Japan and other Asian markets due to alignment with JIS standards. In contrast, SS304 is typically more accessible and economical in the US and Europe, where ASTM specifications dominate. For international buyers, evaluating total cost—including availability, logistics, and certification requirements—is key to selecting the most practical option.
Application Differences (If Any)
In most cases, the choice between SUS304 and SS304 depends more on regional sourcing or standards compliance than on material performance.
- In Japan and East Asia, SUS304 is more prevalent due to domestic standardization under JIS.
- In the US and Europe, SS304 is the default due to AISI/ASTM norms.
When selecting materials for certified products, engineers and purchasing departments must consider:
- Local code requirements
- Material test reports (MTRs) that specify the applicable standards
- Cross-standard equivalency when dealing with international vendors
In global supply chains, the two are typically interchangeable, provided certifications and specifications are aligned.
Summary: Are They Actually Different?
While SUS304 and SS304 are labeled differently, they are essentially the same material in terms of composition, properties, and performance. The distinction lies in the standardizing body—JIS for SUS304 and AISI/ASTM for SS304.
For engineers and purchasers, the key takeaway is this:
- Use SUS304 when following Japanese or Asian specifications.
- Use SS304 when conforming to American or international (ASTM) standards.
When working on international projects, always:
- Verify material equivalency tables
- Ensure certification documents match the project’s standard
- Communicate the equivalence to prevent unnecessary requalification
FAQ about SUS 304 Stainless Steel
Is SUS304 equivalent to SS304?
Yes. Both are 18/8 austenitic stainless steels with the same composition and mechanical behavior. The only difference is the naming standard.
Can SUS304 be used in place of SS304?
In most applications, yes—provided the standard is acceptable for the end user or region. Always confirm with stakeholders or clients before substituting.
Is there any performance difference between SUS304 and SS304?
No significant difference exists. Both offer the same corrosion resistance, strength, and workability. Any variation is due to manufacturing process or heat treatment, not the standard itself.
What are other equivalents to 304 stainless steel?
- EN 1.4301 (European standard)
- X5CrNi18-10 (DIN)
- UNS S30400 (Unified Numbering System)
Will SUS304 stainless steel rust?
SUS304 stainless steel has excellent corrosion resistance, but it can rust under harsh conditions—such as exposure to saltwater, strong acids, or poor maintenance. Regular cleaning and avoiding chloride-rich environments help maintain its rust resistance.
How long will 304 stainless steel last?
304 stainless steel can last decades—often 20 to 50 years or more—depending on the environment and maintenance. In indoor or mildly corrosive settings, it maintains its integrity for decades. However, in harsh conditions like coastal or industrial areas, its lifespan may be reduced without proper care or protective measures.
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