Stainless Steel 304
Stainless steel 304 (UNS S30400) is the most versatile and widely consumed austenitic stainless steel in the world, with an estimated annual production of several million tonnes. Its stable austenitic structure, achieved through a balance of chromium (≈18 %) and nickel (≈8 %), provides excellent formability, weldability and corrosion resistance in a wide variety of environments. It is the predominant choice for the manufacture of deep-drawn parts — such as sinks, kitchenware and hollowware — and in architectural, industrial and transportation components. The 304L (low carbon, UNS S30403) and 304H (high carbon, UNS S30409) variants cover applications requiring welding of thick sections without post-weld heat treatment or service at high temperature, respectively.
Chemical composition
Section titled “Chemical composition”The following table shows the typical chemical composition specified in ASTM A240/A240M for grade 304.
| Element | Composition (wt%) |
|---|---|
| Carbon (C) | ≤ 0,08 |
| Manganese (Mn) | ≤ 2,00 |
| Silicon (Si) | ≤ 0,75 |
| Phosphorus (P) | ≤ 0,045 |
| Sulfur (S) | ≤ 0,030 |
| Chromium (Cr) | 18,0 – 20,0 |
| Nickel (Ni) | 8,0 – 10,5 |
| Nitrogen (N) | ≤ 0,10 |
For grade 304L the maximum carbon limit is 0,030 % and the nickel range is extended to 12,0 %. Grade 304H requires a carbon content between 0,04 and 0,10 % and an ASTM grain size No. 7 or coarser.
Mechanical properties by heat treatment condition
Section titled “Mechanical properties by heat treatment condition”The minimum values given correspond to the annealed condition in flat product (plate, sheet and coil) according to ASTM A240/A240M.
| Property (annealed) | 304 | 304L | 304H | SI Units | Imperial Units |
|---|---|---|---|---|---|
| Tensile strength | 515 | 485 | 515 | MPa | 74,7 ksi |
| Yield strength (0,2 % offset) | 205 | 170 | 205 | MPa | 29,7 ksi |
| Elongation (in 50 mm) | 40 | 40 | 40 | % | — |
| Hardness Rockwell B (max.) | 92 | 92 | 92 | — | — |
| Hardness Brinell (max.) | 201 | 201 | 201 | — | — |
Heavily cold-worked parts can achieve tensile strength values above 1000 MPa, while elongation may decrease to 5-10 %.
Physical properties
Section titled “Physical properties”The following properties have been measured in the annealed condition and at room temperature, unless otherwise stated.
| Property | Value | SI Units | Imperial Units |
|---|---|---|---|
| Density | 8000 | kg/m³ | 0,289 lb/in³ |
| Modulus of elasticity (E) | 193 | GPa | 28,0 × 10⁶ psi |
| Poisson’s ratio (ν) | 0,27 | — | — |
| Electrical resistivity | 720 | nΩ·m | — |
Thermal properties
Section titled “Thermal properties”| Property | Value | SI Units | Imperial Units |
|---|---|---|---|
| Melting range | 1400 – 1450 | °C | 2550 – 2650 °F |
| Specific heat (0‑100 °C) | 500 | J/(kg·K) | 0,12 Btu/(lb·°F) |
| Thermal conductivity at 100 °C | 16,2 | W/(m·K) | 9,36 Btu/(h·ft·°F) |
| Thermal conductivity at 500 °C | 21,5 | W/(m·K) | 12,4 Btu/(h·ft·°F) |
| Mean coefficient of thermal expansion (0‑100 °C) | 17,2 | µm/(m·°C) | 9,56 µin/(in·°F) |
| Mean coefficient of thermal expansion (0‑315 °C) | 17,8 | µm/(m·°C) | 9,89 µin/(in·°F) |
| Mean coefficient of thermal expansion (0‑538 °C) | 18,4 | µm/(m·°C) | 10,2 µin/(in·°F) |
Corrosion resistance
Section titled “Corrosion resistance”Stainless steel 304 offers excellent resistance in most natural atmospheres and in many dilute chemical media. It is susceptible to pitting corrosion and crevice corrosion when exposed to hot chlorides; above about 60 °C it may suffer stress corrosion cracking in environments with more than 150 mg/L of chlorides (the limit at room temperature is around 400 mg/L). It is also very sensitive to thiosulfate anions generated by pyrite oxidation, which can cause severe pitting in contact with sulfide-bearing clays. In applications requiring higher resistance to chlorides or more aggressive acids, grade 316 is recommended.
Applications by industry
Section titled “Applications by industry”| Sector | Typical applications |
|---|---|
| Kitchen and catering | Sinks, cookware, cutlery (18/10), sanitary accessories |
| Architecture and construction | Decorative panels, railings, door and window frames, locksmithing |
| Automotive and transport | Trim, moldings, exhaust components, fuel tanks |
| Chemical and food industry | Tanks, pipes, heat exchangers, pressure vessels, fermentation vats |
| Aerospace and cryogenics | Structural components, joints, ducts for liquefied gases |
| Appliances and consumer goods | Washing machine drums, dishwasher tubs, small appliance housings |
| Medical equipment | General surgical instruments, hospital furniture |
Weldability
Section titled “Weldability”Stainless steel 304 has excellent weldability by all conventional processes (TIG, MIG, shielded metal arc, resistance). In thin sections (≤ 6 mm) post-weld heat treatment is not necessary because the risk of chromium carbide precipitation is low. For thicker sections or when service conditions may cause intergranular corrosion, grade 304L is used, whose low carbon content eliminates the need for subsequent annealing. Grade 304H, used in boiler making and components operating at elevated temperatures, is generally welded without subsequent treatments as long as design temperatures are kept within permissible limits.
Comparison with similar materials
Section titled “Comparison with similar materials”| Material | Why can it be chosen over 304? |
|---|---|
| 301L | Greater work-hardening capacity; suitable for roll-formed or drawn parts requiring high mechanical strength. |
| 304L | Minimal tendency to carbide precipitation; recommended for thick-section welds without annealing and in environments that may induce intergranular corrosion. |
| 304H | Better mechanical and creep strength at high temperature; used in boiler making and components exposed to more than 400 °C. |
| 316 | Much superior pitting corrosion resistance thanks to the addition of molybdenum (≈2,5 %); indicated for marine environments and chemical processes with chlorides. |
| 321 | Stabilized with titanium; avoids intergranular corrosion in high-temperature applications (500‑800 °C) without requiring low carbon content. |
| 430 (ferritic) | Magnetic steel, no nickel; lower cost than 304 and good corrosion resistance indoors; used in appliances and cladding when high formability is not required. |
International equivalents
Section titled “International equivalents”| Grade | UNS | EN (Steel) | JIS (Japan) | BS (UK) | SS (Sweden) |
|---|---|---|---|---|---|
| 304 | S30400 | 1.4301 (X5CrNi18‑10) | SUS 304 | 304S31 | 2332 |
| 304L | S30403 | 1.4306 (X2CrNi19‑11) | SUS 304L | 304S11 | 2352 |
| 304H | S30409 | 1.4948 (X6CrNi18‑11) | — | 304S51 | — |
These equivalents are for guidance; for exact requirements the original standards of each country must be consulted.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the minimum tensile strength of stainless steel 304 in the annealed condition?
Section titled “What is the minimum tensile strength of stainless steel 304 in the annealed condition?”The minimum value per ASTM A240 is 515 MPa (74,7 ksi), and much higher values can be achieved after cold working.
What is the density of 304 steel and how does it affect component weight?
Section titled “What is the density of 304 steel and how does it affect component weight?”The density is 8000 kg/m³ (0,289 lb/in³), which is approximately 2 % more than that of carbon steel; one cubic meter of 304 weighs 8000 kg.
At what temperature does 304 melt?
Section titled “At what temperature does 304 melt?”The melting range is between 1400 and 1450 °C (2550‑2650 °F), typical of austenitic steels with high chromium and nickel content.
What is the thermal conductivity of 304 and how does it vary with temperature?
Section titled “What is the thermal conductivity of 304 and how does it vary with temperature?”At 100 °C the conductivity is 16,2 W/(m·K) (9,36 Btu/(h·ft·°F)), increasing to 21,5 W/(m·K) (12,4 Btu/(h·ft·°F)) at 500 °C; these values are significantly lower than those of carbon steel.
Is stainless steel 304 magnetic?
Section titled “Is stainless steel 304 magnetic?”In the annealed condition it is practically non-magnetic (magnetic permeability close to 1) due to its austenitic structure; after heavy cold working it may develop slight magnetism.
What chromium and nickel content defines 304?
Section titled “What chromium and nickel content defines 304?”Chromium is in the range 18‑20 % and nickel between 8 and 10,5 %, giving rise to the well-known commercial designations “18/8” or “18/10”.
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?articleid=965
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/stainless-steel-310-properties-d_2167.html
- steelnumber.com: https://www.steelnumber.com/en/equivalent_steel_iron_eu.php?zname_id=880