SUS316 vs SUS304: Key Differences in Composition, Properties and Applications

SUS316 and SUS304: Two Workhorses of the Austenitic Family

SUS304 and SUS316 are both austenitic stainless steels with a face-centered cubic structure that makes them non-magnetic in the annealed condition and formable over a wide temperature range. The fundamental difference between the two is chemistry: SUS316 is essentially SUS304 with a deliberate molybdenum addition of 2.00-3.00%. This single change shifts the alloy from a general-purpose grade to a higher-corrosion-resistance grade for chloride-bearing service.

What Is SUS304 Stainless Steel?

SUS304 is the Japanese designation of the 18-8 austenitic stainless steel, containing approximately 18% chromium and 8% nickel. It offers excellent general corrosion resistance, good mechanical properties and outstanding formability and weldability, at a comparatively low cost. In the Chinese GB system it corresponds to 06Cr19Ni10. SUS304 is the default choice for kitchenware, food processing equipment, building interiors and countless general engineering components, but it is not resistant to chloride pitting, crevice corrosion or stress corrosion cracking.

What Is SUS316 Stainless Steel?

SUS316 is an austenitic stainless steel alloyed with molybdenum for enhanced corrosion resistance. The molybdenum content of 2.00-3.00% significantly improves resistance to pitting and crevice corrosion in chloride media such as seawater and de-icing salts, and improves strength at elevated temperature. In the Chinese GB system it corresponds to 06Cr17Ni12Mo2. Typical applications include chemical equipment, marine hardware, medical devices, pharmaceutical equipment and heat exchangers.

Chemical Composition (JIS G4304 / G4305)

Element, %	SUS304	SUS316
Carbon C	0.08 max	0.08 max
Silicon Si	1.00 max	1.00 max
Manganese Mn	2.00 max	2.00 max
Phosphorus P	0.045 max	0.045 max
Sulfur S	0.030 max	0.030 max
Nickel Ni	8.00-10.50	10.00-14.00
Chromium Cr	18.00-20.00	16.00-18.00
Molybdenum Mo	-	2.00-3.00

Note that SUS316 carries a higher nickel range and a slightly lower chromium range than SUS304, with the balance adjusted by the molybdenum addition.

Mechanical Properties (JIS G4304, Plate)

Property	SUS304	SUS316
0.2% proof stress, MPa	205 min	205 min
Tensile strength, MPa	520 min	520 min
Elongation, %	40 min	40 min
Hardness	187 HB / 90 HRB / 200 HV max	187 HB / 90 HRB / 200 HV max

Physical Properties

Property	SUS304	SUS316
Density, g/cm3	7.93	7.98
Modulus of elasticity, GPa	193	193
Thermal conductivity at 100 C, W/m.K	16.3	16.3
Melting range, degrees C	approximately 1400-1450	approximately 1371-1399

SUS316 has a slightly lower melting range than SUS304 because of its higher alloy content. This is rarely a design consideration in normal service, since neither grade is used near its melting point.

Corrosion Resistance and Cost

The molybdenum in SUS316 gives it clearly better resistance to pitting and crevice corrosion in chloride environments. In practical terms, SUS316 is preferred for coastal construction, marine fittings, chemical equipment and any application exposed to salt or chlorine-based cleaning agents. Because nickel and molybdenum are expensive alloying elements, SUS316 typically costs noticeably more than SUS304, and its higher nickel content makes its price more sensitive to raw material market movements.

Application Comparison

SUS304: kitchenware, food processing, beverage lines, building facades, railings, household appliances, general storage tanks in non-chloride service.

SUS316: chemical and pharmaceutical equipment, marine and offshore hardware, heat exchangers, medical instruments, seawater piping, brewery and dairy equipment cleaned with chlorine.

Comparison with Other JIS Grades

SUS430 is a ferritic grade that is magnetic and has lower corrosion resistance than both SUS304 and SUS316, but it is inexpensive and widely used for kitchen sinks and appliance panels. SUS303 is a free-machining version of SUS304 with added sulfur; it machines easily but has lower corrosion resistance and formability. SUS310S is a high-nickel, high-chromium heat-resistant grade with better high-temperature oxidation resistance than SUS316, at a correspondingly higher cost.

Frequently Asked Questions

Q1. Is SUS316 always better than SUS304?

Not for every application. SUS316 has superior chloride and pitting resistance, but for dry interiors, food contact without aggressive cleaning agents, and general atmospheric service, SUS304 provides equivalent performance at lower cost. Selection should be based on the actual service environment.

Q2. Are SUS304 and SUS316 magnetic?

Both are austenitic and essentially non-magnetic in the annealed condition. Cold working such as heavy forming or machining can transform part of the structure to martensite, making the material slightly magnetic. Ferritic grades such as SUS430 are strongly magnetic.

Q3. How can I tell SUS304 and SUS316 apart?

Visually the two are identical. Reliable identification requires a mill test certificate or a chemical spot test for molybdenum. A laboratory analysis per JIS G1253 or similar is definitive.

Q4. What does 18-8 stainless steel mean?

It refers to the approximate composition of SUS304: about 18% chromium and 8% nickel. The term is used loosely for the 304 family, including low-carbon and stabilized variants.

Q5. Can SUS316 be used in seawater?

In mild marine atmospheres and splash zones, SUS316 performs well. For permanent immersion in seawater or in stagnant, creviced conditions, pitting and crevice corrosion can still occur, and higher-alloy materials such as 6% molybdenum super-austenitic or duplex grades are usually specified.

Q6. Why is SUS316 more expensive than SUS304?

Because of the higher nickel content and the addition of molybdenum, both of which are costly alloying elements. The price difference fluctuates with nickel and molybdenum market prices.