JIS SUS304 vs ASTM 304: How Do These Stainless Grades Actually Compare?

The manufacturing industry treats JIS SUS304 and ASTM 304 as interchangeable 18/8 austenitic stainless steels, yet they are not identical. Like most standards, the two have quite unique metallurgical and regulatory differences. Probably the reason you might think they are interchangeable is because their physical performance is almost similar.

However, you already know that chemical limits and density calculations matter when working with metal. For this reason, evaluating their unique properties will help you avoid certification failures, shipping weight errors, and compliance violations. This article highlights the specific chemical, mechanical, and supply chain differences you must account for when sourcing across Asian and North American markets.

Understanding JIS and ASTM Naming Systems

You need to first understand the regulatory codes to procure safely in the global steel market. There are rigorous legal frameworks you must follow that dictate how material is tested and certified.

What is SUS304?

SUS is an abbreviation for Steel Use Stainless. This is the prefix used by the Japanese Industrial Standards (JIS) to classify stainless steel grades. The JIS framework, governed by the Japanese Industrial Standards Committee (JISC), is the dominant standard in Japan and deeply integrated into supply chains across South Korea, China, and Southeast Asia.

Note that SUS304 is not a single specification. Instead, it is a chemical grade baseline applied to specific product forms.

For example:

• 1）JIS G4303 governs stainless steel bars.
• 2）JIS G4304 governs hot-rolled plates and sheets.
• 3）JIS G4305 governs cold-rolled sheets.

When you purchase SUS304 from an Asian mill, the material is tested against the dimensional tolerances and defect limits of these specific G-series standards.

What is ASTM 304 (SS304)?

ASTM International sets the primary standards for the North American and Middle Eastern markets. The "304" designation originates from the AISI (American Iron and Steel Institute) 300-series numbering system for austenitic stainless steels.

You will frequently see SS304 on blueprints or in email conversations. Keep in mind that SS304 is a casual abbreviation for Stainless Steel 304, meaning, it is not a legally binding standard. Valid purchase orders must reference the specific ASTM specification, such as ASTM A240 (for plate, sheet, and strip used in pressure vessels) or ASTM A276 (for bars).

Where Does UNS S30400 Fit?

The Unified Numbering System (UNS) was developed to resolve the confusion created by competing regional designations. Under this system, standard 304 is designated as UNS S30400.

Think of UNS S30400 as the common umbrella. If a melt of steel falls within the chemical limits of UNS S30400, it can theoretically be certified as either JIS SUS304 or ASTM 304, provided it meets the specific testing protocols of those standards.

Chemical Composition of JIS SUS304 vs ASTM 304

The chemical composition is where you will often encounter technical non-conformance. While the alloys are chemically similar, the allowed limits are different. A heat of steel can legally pass ASTM standards while failing JIS standards (and vice versa).

Here is a table showing the compositions of the two.

Carbon and Silicon Variances

ASTM A240 restricts Carbon to 0.07% to provide a safety margin against sensitization carbide precipitation during welding. JIS allows up to 0.08%. On the other hand, JIS allows significantly more Silicon (≤ 1.00%) than ASTM (≤ 0.75%). Since Silicon acts as a deoxidizer, this difference can affect high-temperature oxidation resistance, though for most ambient structural applications, this is a minor difference.

Mechanical Comparison of JIS SUS304 vs ASTM 304

When analyzing mechanical properties, co nfusion usually comes from testing methodology rather than material performance. The steel behaves the same way physically, but the lab reports will display different numbers due to how the tests are conducted.

Let us compare the actual numbers.

The Testing Standard Divergence

The yield and tensile strengths are identical, but differences appear in Elongation values.

• --- ASTM E8: Typically uses a fixed gauge length (often 2 inches or 50mm).
• --- JIS Z 2241: Often uses a proportional gauge length, calculated as L0 = 5.65 * √S0, where S0 is the cross-sectional area.

Because ductility depends on the test specimen geometry, a JIS test report and an ASTM test report for the exact same coil of steel may list different elongation percentages. As such, you must verify which testing standard between ASTM E8 or JIS Z 2241, was applied if your application demands precise deep-drawing limits.

The Differences in Standards, Documentation, and Supply Chain

Beyond chemistry and physics, the choice between JIS and ASTM impacts your paperwork, shipping costs, and lead times.

Standardization Framework

In the US, ASTM A240 is the technical foundation of the ASME Boiler and Pressure Vessel Code (BPVC). Historically, this meant you could only use ASTM materials for pressure components. However, supply chain globalization forced a change.

ASME BPVC code case N-708 now permits the use of JIS G4303 grades SUS304 and SUS304L for Class 1 construction. This is a crucial regulatory exemption. It validates that top-tier Western safety bodies recognize the metallurgical safety of the Japanese standard, provided the documentation is perfect.

Mill Test Certificates and Documentation

Suppliers use dual certification to be on the safe side. Modern Argon Oxygen Decarburization (AOD) refining allows mills to easily produce 304 grades with very low carbon (e.g., 0.02%) and high chromium (18.5%).

Because this chemistry satisfies the strict Carbon limit of "L" grades and the strength requirements of standard grades, the Mill Test Report (MTR) will certify the material as 304/304L.

It will also often list compliance with both ASTM and JIS standards if the Cr/Ni levels are high enough. During procurement, you should specifically request dual-certified MTRs to ensure the inventory works for both US and Asian project specs.

Regional Availability and Lead Times

Lead times and availability depend on geography.

• --- Asia: JIS SUS304 is the main stock. Sourcing ASTM-specific material in China or Vietnam may require a special mill run or a comprehensive re-certification process, adding 3–5 weeks to lead times to your procurement process.
• --- North America: ASTM 304 is the default. Sourcing JIS material often requires importing, subjecting you to oceanic transit times of 6–12 weeks.

Cost Differences and Density Calculations

Pricing is driven by tariffs, like Section 232 in the US and raw material access (Indonesian Nickel Pig Iron feeding Asian mills). As a result, Asian FOB prices for SUS304 are frequently 30-50% lower than US domestic ASTM 304 prices.

However, density is a hidden factor that affects cost.

• --- ASTM often uses a nominal density of 7.9 g/cm³ or relies on theoretical imperial conversions.
• --- JIS particularly dictates a density of 7.93 g/cm³ for mass calculations.

This 0.4-0.8% difference seems minor until you buy 10,000 metric tons. The billing weight on a JIS invoice will differ from an ASTM invoice for the same physical volume of steel. For this reason, you must clarify the agreed-upon density for weight calculation in your purchasing contract to avoid billing disputes.

When to Use JIS SUS304 vs ASTM 304

Your choice should depend on where the fabrication occurs and who certifies the final assembly.

Use SUS304 When:

• --- Sourcing and manufacturing in Asia: If you are machining components in Vietnam or stamping parts in Japan, specify SUS304. Local service centers stock this as their primary inventory.
• --- Cost is the primary driver: For commercial goods (cookware, trim, non-pressure applications), utilizing Asian SUS304 supply chains avoids Western premiums and tariffs.
• --- Precise dimensional requirements: Japanese standards often govern the exact millimeter thickness of plates or the precise schedule sizes of piping infrastructure, which may not perfectly align with American standard sheet gauge charts or nominal pipe sizes.

Use ASTM 304 (SS304) When:

• --- ASME or regulatory compliance is mandatory: Unless specifically exempted by specific code cases like N-708, pressure vessels, pharmaceutical reactors, and nuclear components in the US legally require ASTM-certified materials traced by flawlessly compliant MTRs to protect against liability.
• --- Operating in the US domestic market: Despite the higher cost, projects subjected to Buy American provisions or defense contracts must utilize domestic ASTM 304 to ensure supply chain resilience and legal compliance.
• --- Specific testing protocols are demanded: If your engineering design explicitly relies on yield point and elongation limits derived strictly from ASTM E8 50mm gauge length methodologies, utilizing ASTM material removes variable testing inconsistencies in foreign standards.

Either Works When:

• --- The Material is dual-certified (UNS S30400): If you secure an MTR proving the heat contains 18.00% Chromium, <0.07% Carbon, and meets all mechanical minimums, the material legally satisfies both JIS G4304 and ASTM A240.
• --- General fabrication: For structural welding (TIG/MIG), sink manufacturing, or cryogenic applications, both materials exhibit identical formability and toughness.
• --- Standard surface finishes are required: Whether you need a standard 2B finish, a reflective Bright Annealed (BA) finish, or a decorative Hairline (HL), the processing techniques and final Ra (roughness) values are equivalent across both frameworks.

Frequently Asked Questions