SUS304 is a Japanese Industrial Standard (JIS) designation for the most widely used grade of stainless steel in the world. “SUS” stands for “Steel Use Stainless,” and “304” identifies the specific alloy composition. If you’ve seen this stamped on a kitchen sink, a water bottle, or an appliance label, it refers to the same stainless steel known as AISI 304 in the United States, 1.4301 in Europe, and commonly marketed as “18/8 stainless steel.”
What the Name Breaks Down To
The JIS naming system is straightforward. “Steel Use Stainless” is the material category, and the number 304 specifies a particular recipe of metals. That recipe, governed by JIS G4305-2021, requires 18–20% chromium and 8–10.5% nickel, with small amounts of carbon, silicon, and manganese. The “18/8” nickname you often see on cookware comes directly from those two key ingredients: roughly 18% chromium and 8% nickel.
This designation is most common in Japan and across Asian markets. If you’re comparing products from different countries, SUS304 is functionally identical to AISI 304 (the American standard), EN 1.4301 (the European standard), and UNS S30400. A pot labeled SUS304 in Japan and one labeled 304 in the U.S. are made from the same alloy.
Why SUS304 Resists Rust
The chromium in SUS304 reacts with oxygen in the air to form an extremely thin, invisible layer of chromium oxide on the steel’s surface. This layer acts as a shield, blocking moisture and corrosive substances from reaching the iron underneath. What makes it especially useful is that this protective film is self-healing. If the surface gets scratched, chromium in the exposed steel immediately reacts with air to rebuild the barrier.
This is why SUS304 handles contact with acids in fruits, vegetables, meat, and dairy without corroding. It also performs well in marine environments and outdoor settings where constant exposure to moisture would quickly rust ordinary steel.
Mechanical Strength and Flexibility
SUS304 is strong enough for structural and industrial use while remaining easy to shape. Its ultimate tensile strength sits around 505 MPa (about 73,200 psi), with a yield strength of 215 MPa. In practical terms, it holds up well under load without being brittle. Its elongation at break is roughly 70%, meaning it can stretch significantly before failing. This combination of strength and flexibility is why manufacturers can deep-draw it into complex shapes like sinks, cookware, and medical instruments without the metal cracking.
Where You’ll Find It
SUS304 is the default choice for an enormous range of products. In the kitchen, it’s the steel behind pots, pans, mixing bowls, cutlery, refrigerator panels, and dishwasher interiors. Its resistance to food acids and easy cleaning make it the standard material for commercial food processing equipment as well.
Beyond the home, SUS304 shows up in fasteners, bolts, piping, chemical storage tanks, brewery equipment, and architectural panels. Its corrosion resistance makes it popular for outdoor railings, building facades, and marine hardware. If a product description mentions “food-grade stainless steel” without specifying a grade, it’s almost always 304 or its close relative 316.
Temperature Limits
SUS304 handles heat well, with good oxidation resistance up to about 870°C (1,600°F) in intermittent use and 925°C (1,700°F) in continuous service. For most cooking and household applications, these limits are far beyond anything you’d encounter. One caveat: sustained use in the 425–860°C range can reduce the steel’s corrosion resistance afterward, which matters in industrial settings but not in everyday home use.
Is SUS304 Magnetic?
In its standard form, SUS304 is not magnetic. The internal crystal structure of the alloy (called austenite) is paramagnetic, meaning a refrigerator magnet won’t stick to it. This sometimes confuses people who assume all steel is magnetic.
However, SUS304 can become slightly magnetic if it’s been cold-worked, meaning mechanically deformed through processes like rolling, bending, or stamping. Cold working transforms some of the austenite into a different crystal structure called martensite, which is ferromagnetic. The more the steel has been worked, the stronger this effect. Heating the steel above about 500°C reverses the transformation and eliminates the magnetism. So if a magnet weakly clings to your SUS304 water bottle, it’s not counterfeit. It just means the steel was shaped through a process that introduced some magnetic character.
SUS304 vs. SUS316
The other grade you’ll frequently see is SUS316 (or just 316). The key difference is that 316 adds 2–3% molybdenum, which gives it better resistance to salt water and chloride-based corrosion. For coastal environments, swimming pool equipment, or medical implants, 316 is the better choice. For kitchens, general construction, and most everyday products, SUS304 offers more than enough corrosion protection at a lower cost. The price gap between the two is typically 20–40%, which is why 304 remains the world’s most produced stainless steel grade.