AISI 304 stainless steel (UNS S30400, SS 304)
AISI 304 stainless steel (UNS S30400) is the most widely used stainless steel, containing 18-20% Cr and 8-10.5% Ni, and also known as 18-8 stainless steel. SS 304 is not magnetic under annealing conditions, but after cold working (such as stamping, stretching, bending, rolling), part of the austenite structure can be converted to martensite and is therefore weakly magnetic. Type 304 has good resistance to corrosion and atmospheric oxidation. The high nickel-chromium alloy content gives it excellent corrosion resistance and is widely used in the food industry as standard food-grade stainless steel.
There are several variants of grade 304 stainless steel, such as type 304L ultra-low carbon version, 304N nitrogen-containing version, 304H with improved creep performance and type 302 with higher carbon content. The second most used grade 316 stainless steel, compared to AISI 304, has reduced chromium content, increased nickel content and added 2-3% molybdenum. The addition of molybdenum can increase resistance to pitting and crevice corrosion caused by chloride. Therefore, the 316 SS is widely used in marine applications.
SS 304 Stainless Steel Properties
The following tables provide properties and specifications of SS 304 stainless steel (data sheet), including chemical composition, physical and mechanical properties, heat treatment, corrosion resistance, machinability and machining, welding, etc.
Chemical composition
The chemical composition of AISI 304 stainless steel is listed in the following table.
| Composition of type 304 stainless steel, % | |||||||||
| ASTM Standard | AISI (UNS) | C, ≤ | Yes, ≤ | Mn, ≤ | P, ≤ | S, ≤ | Cr | No | N, ≤ |
| ASTM A240/A240M | 304 (UNS S30400) | 0.07 | 0.75 | 2:00 | 0.045 | 0.03 | 17.5-19.5 | 8.0-10.5 | 0.1 |
| ASTM A276/A276M | 0.08 | 1.00 | 2:00 | 0.045 | 0.03 | 6pm-8pm | 8.0-11.0 | – | |
| ASTM 666; SAE J405 |
0.08 | 0.75 | 2:00 | 0.045 | 0.03 | 6pm-8pm | 8.0-10.5 | 0.1 | |
| ASTM A313/A313M | 0.08 | 1.00 | 2:00 | 0.045 | 0.03 | 6pm-8pm | 8.0-10.5 | 0.1 | |
| ASTM A479/A479M | 0.08 | 1.00 | 2:00 | 0.045 | 0.03 | 6pm-8pm | 8.0-10.5 | – | |
| ASTM A314; ASTM A580/A580M |
0.08 | 1.00 | 2:00 | 0.045 | 0.03 | 6pm-8pm | 8.0-10.5 | 0.1 | |
| ASTM A473 | 0.08 | 1.00 | 2:00 | 0.045 | 0.03 | 6pm-8pm | 8.0-11.0 | 0.1 | |
| ASTM A959 | 0.07 | 1.00 | 2:00 | 0.045 | 0.03 | 17.5-19.5 | 8.0-11.0 | – | |
Grades:
- ASTM A240/A240M : Chromium and chrome-nickel stainless steel plates, sheets and strips for pressure vessels and general applications
- ASTM A276/A276M : Stainless Steel Bars and Forms
- ASTM A313/A313M : Stainless Steel Spring Wire
- ASTM A314 : Stainless Steel Billets and Bars for Forging
- ASTM A473 : Stainless Steel Forgings
- ASTM A479/A479M : Stainless steel bars and shapes for use in boilers and other pressure vessels
- ASTM A580/A580M : Stainless Steel Wire
- ASTM 666 : Annealed or cold worked austenitic stainless steel sheet, strip, plate and flat bar
- ASTM A959 : Standard Guide for Specification of Harmonized Standard Grade Compositions for Wrought Stainless Steels
- SAE J405 : Chemical Composition of SAE Forged Stainless Steels
Physical properties
The physical properties of SS 304 stainless steel are listed in the table below, such as density, melting point, specific heat, electrical resistivity, modulus of elasticity (modulus of elasticity), thermal conductivity and coefficient of thermal expansion (CTE).
Grades:
- 10 -6 ·K -1 = 10 -6 /K
- 1Ω mm²/m = 1 μΩ m
- 1 g/cm3 = 1 kg/dm3 = 1000 kg/m3
- 1 GPa = 1kN/mm2
- 1 MPa = 1 N/mm2
| Physical Properties of Type 304 Stainless Steel | |
| Density, g/cm3 (lb/in3) | 7.93 (0.286) |
| Melting point, °C (°F) | 1400-1450 (2550-2650) |
| Specific heat capacity, J/kg·K (Btu/lb ·°F) | 500 (0.12) at 20°C (68°F) |
| Electrical resistivity, μΩ·m | 0.72 at 20°C (68°F) |
| Conductivity, %, IACS | 2.5 |
| Magnetic permeability | 1.02 (approximate) |
| Elastic Modulus (Modulus of Elasticity), GPa (10 6 psi) | 193 (28) |
| Thermal diffusivity, mm2/s (in2/s) | 3.84 (0.006) |
| Thermal conductivity, W/m·K (Btu/ft·h·°F) | 16.2 (9.4) at 100°C (212°F) |
| 21.5 (12.4) at 500°C (932°F) | |
| Coefficient of thermal expansion (CTE), 10 -6 /K (μin./in·°F) | 17.2 (9.6) at 0-100°C (32-212°F) |
| 17.8 (9.9) at 0-315°C (32-600°F) | |
| 18.4 (10.2) at 0-538°C (32-1000°F) | |
Mechanical properties of AISI 304 stainless steel
The mechanical properties of AISI 304 stainless steel are given in the data sheet below, including tensile strength, yield strength, elongation, area reduction, Brinell and Rockwell hardness, etc.
Data comes from professional, authoritative and reliable ASTM standards.
| Mechanical Properties of ASTM A276 Type 304 Stainless Steel | ||||||
| ASTM | AISI (UNS) | Tensile strength, Mpa (ksi), ≥ | 0.2% yield strength, Mpa (ksi), ≥ | Stretch by 2 in. (50 mm), %, ≥ | Area Reduction, %, ≥ | Conditions |
| ASTM A276/A276M | 304 (UNS S30400), 304LN (UNS S30453) |
515 (75) | 205 (30) | 40 | 50 | Annealed, hot finished |
| 620 (90) | 310 (45) | 30 | 40 | Annealed, cold finished, diameter ≤ 1/2 in. (12.7mm) | ||
| 515 (75) | 205 (30) | 30 | 40 | Annealed, cold finished, diameter > 1/2 in. (12.7mm) | ||
| Mechanical Properties of ASTM A240 Type 304 Steel | ||||||
| ASTM | AISI (UNS) | Tensile strength, Mpa (ksi), ≥ | 0.2% yield strength, Mpa (ksi), ≥ | Stretch by 2 in. (50 mm), %, ≥ | Brinell hardness, HB, ≤ | Rockwell hardness, HRB, ≤ |
| ASTM A240/A240M | 304 (UNS S30400) | 515 (75) | 205 (30) | 40 | 201 | 92 |
| ASTM A666 Type 304 Mechanical Properties | |||||||
| ASTM Standard | AISI type (UNS) | Conditions | Tensile strength, MPa (ksi), ≥ | 0.2% yield strength, MPa (ksi), ≥ | Elongation by 50 mm (2 in.), %, ≥ | Brinell hardness (HB), ≤ | Rockwell hardness (HRB), ≤ |
| ASTM A666 | 304 (UNS S30400) | Annealed | 517 (75) | 205 (30) | 40 | 201 | 92 |
| 1/2 Hard (Medium Hard) | 1035 (150) | 760 (110) | 6 (<0.015 in.); 7 (≥ 0.015 in.) |
||||
| 1/4 (a quarter hard) hard | 862 (125) | 517 (75) | 10 (≤ 0.03 in.); 12 (> 0.03 in.) |
||||
| 1/8 Hard | 690 (100) | 380 (55) | 35 | ||||
| plate, strip, sheet | 1/16 Hard | 550 (80) | 310 (45) | 40 | |||
| 304 flat bar | 620 (90) | 310 (45) | 40 (>0.030 in.) | ||||
| Type 304 stainless steel spring wire tensile strength requirements of ASTM A313 | ||||
| Diameter (d), in. | Diameter (d), mm | Bending test, minimum number of bends | ksi | MPa |
| ≤0.009 | ≤0.23 | – | 325-355 | 2240-2450 |
| 0.009 |
0.23 |
– | 320-350 | 2205-2415 |
| 0.010 |
0.25 |
– | 318-348 | 2190-2400 |
| 0.011 |
0.28 |
– | 316-346 | 2180-2385 |
| 0.012 |
0.30 |
– | 314-344 | 2165-2370 |
| 0.013 |
0.33 |
– | 312-342 | 2150-2360 |
| 0.014 |
0.36 |
– | 310-340 | 2135-2345 |
| 0.015 |
0.38 |
– | 308-338 | 2125-2330 |
| 0.016 |
0.41 |
– | 306-336 | 2110-2315 |
| 0.017 |
0.43 |
– | 304-334 | 2095-2300 |
| 0.018 |
0.46 |
– | 300-330 | 2070-2275 |
| 0.020 |
0.51 |
– | 296-326 | 2040-2250 |
| 0.022 |
0.56 |
– | 292-322 | 2015-2220 |
| 0.024 |
0.61 |
– | 291-320 | 2005-2205 |
| 0.026 |
0.66 |
8 | 289-318 | 1995-2190 |
| 0.028 |
0.71 |
8 | 285-315 | 1965-2170 |
| 0.031 |
0.79 |
8 | 282-310 | [1945-2135 |
| 0.034 |
0.86 |
8 | 280-308 | 1930-2125 |
| 0.037 |
0.94 |
8 | 275-304 | 1895-2095 |
| 0.041 |
1.04 |
8 | 272-300 | 1875-2070 |
| 0.045 |
1.14 |
8 | 267-295 | 1840-2035 |
| 0.050 |
1.27 |
8 | 265-293 | 1825-2020 |
| 0.054 |
1.37 |
7 | 261-289 | 1800-1990 |
| 0.058 |
1.47 |
7 | 258-285 | 1780-1965 |
| 0.063 |
1.60 |
7 | 252-281 | 1735-1935 |
| 0.070 |
1.78 |
7 | 250-278 | 1725-1915 |
| 0.075 |
1.90 |
7 | 246-275 | 1695-1895 |
| 0.080 |
2.03 |
7 | 242-271 | 1670-1870 |
| 0.087 |
2.21 |
7 | 238-268 | 1640-1850 |
| 0.095 |
2.41 |
5 | 232-262 | 1600-1805 |
| 0.105 |
2.67 |
5 | 227-257 | 1565-1770 |
| 0.115 |
2.92 |
5 | 222-253 | 1530-1745 |
| 0.125 |
3.17 |
3 | 217-248 | 1495-1710 |
| 0.135 |
3.43 |
3 | 210-241 | 1450-1660 |
| 0.148 |
3.76 |
3 | 205-235 | 1415-1620 |
| 0.162 |
4.11 |
3 | 198-228 | 1365-1570 |
| 0.177 |
4.50 |
1 | 194-225 | 1335-1550 |
| 0.192 |
4.88 |
1 | 188-220 | 1295-1515 |
| 0.207 |
5.26 |
1 | 182-214 | 1255-1475 |
| 0.225 |
5.72 |
1 | 175-205 | 1205-1415 |
| 0.250 |
6.35 |
1 | 168-198 | 1160-1365 |
| 0.278 |
7.06 |
1 | 161-192 | 1110-1325 |
| 0.306 |
7.77 |
1 | 155186 | 1070-1280 |
| 0.331 |
8.41 |
1 | 150-180 | 1035-1240 |
| 0.362 |
9.19 |
1 | 145-175 | 1000-1205 |
| 0.394 |
10:00 |
1 | 140-170 | 965-1170 |
| 0.438 |
11.12 |
1 | 135-165 | 930-1140 |
| >0.500 | >12.70 | – | 130-160 | 895-1105 |
| When wire is specified in straightened and cut lengths, the minimum tensile strength shall be 90% of the values listed in the table. | ||||
| Mechanical Properties ASTM A473 Type 304 | |||||||
| ASTM | AISI (UNS) | Tensile strength, Mpa (ksi), ≥ | 0.2% yield strength, Mpa (ksi), ≥ | Stretch by 2 in. (50 mm), %, ≥ | Area Reduction, %, ≥ | Sections | Conditions |
| ASTM A473/A473M | 304 (UNS S30400) | 515 (75) | 205 (30) | 40 | 50 | ≤ 5 in. (127mm) | Annealed |
| 485 (70) | > 5 in. (127mm) | Annealed | |||||
| Mechanical Properties ASTM A479 Type 304 | ||||||
| ASTM | AISI (UNS) | Tensile strength, Mpa (ksi), ≥ | 0.2% yield strength, Mpa (ksi), ≥ | Stretch by 2 in. (50 mm), %, ≥ | Area Reduction, %, ≥ | Conditions |
| ASTM A479/A479M | 304, 304H, 304LN | 515 (75) | 205 (30) | 30 | 40 | Annealed |
| ASTM A580 Type 304 Mechanical Properties | ||||||
| ASTM | AISI (UNS) | Tensile strength, Mpa (ksi), ≥ | 0.2% yield strength, Mpa (ksi), ≥ | Stretch by 2 in. (50 mm), %, ≥ | Area Reduction, %, ≥ | Conditions |
| ASTM A580/A580M | SS304 (UNS S30400) | 620 (90) | 310 (45) | 30 | 40 | Annealed, cold finished |
| 515 (75) | 205 (30) | 35 | 50 | Annealed | ||
Type 304 stainless steel heat resistance
| Maximum service temperature in air | ||
| AISI type | Intermittent service | Continuous service |
| 304 | 870°C (1600°F) | 925°C (1700°F) |
Hardening
Conventional austenite such as AISI 304 stainless steel cannot be hardened by heat treatment as it does not change its crystalline structure when heated, therefore it can only be hardened by cold working. Cold working will transform some of the austenite into martensite. As the amount of martensite in steel increases, its strength increases and its plasticity decreases.
Corrosion resistance
The reason why SS 304 material does not rust is because the Cr and Fe contained in it are oxidized to form a dense passive film to prevent further corrosion.
AISI 304 stainless steel has excellent corrosion resistance in mild atmosphere and fresh water, and even the surface does not rust. But it is not resistant to halide corrosion (such as chloride, fluorine, etc.), because the halide can easily penetrate the passive film and make the stainless steel lose strength.
AISI 304 grade stainless steel welding
Type 304 stainless steel has excellent weldability and does not require preheating. Post-weld heat treatment is generally not necessary unless large cross-sections are welded, or weld deterioration may occur.
To prevent weld deterioration, refer to heat treatment stress relief or recommend using ultra-low carbon stainless steel such as 304L or stabilized stainless steel 321, 347.
Filler metal for welding AISI 304 material: E308, E309. When the service temperature is 370 °C (700 °F), the E308L can be used.
Typical Applications
AISI 304 stainless steel is widely used in food industry, household appliances and consumer electronics, medical equipment, architectural decoration, hardware tools, automotive industry, petrochemical industry, water treatment plants, aerospace, etc.
- Food industry: cutlery and kitchen utensils such as stainless steel woks, steamers, pans, forks, chopsticks, baking trays, barbecue grills, dairy containers, sterilization baskets.
- Electronic appliances: electric kettle SS 304 liner, washing machine drum, watch and cell phone case, microwave oven, range hood cover, control cabinet, water pump box, etc.
- Medical equipment: medical cabinets, medical carts, sterilization container, work table, etc.
- Hardware tools: stainless steel screws and nuts, spring steel, hardware screen, window screens, scissors, faucets, shower heads, security screen;
- Water treatment plants: valves, flanges, water pipes, water purification equipment.
- Petrochemical industry: filtration equipment, oil and gas pipelines.
Degree equivalent to AISI 304
Type 304 stainless steel equivalent to European EN (German DIN, British BSI, French NF…), ISO, Japanese JIS and Chinese GB standard (for reference).
| AISI 304 stainless steel equivalent grade | |||||||||||||||
| USA | European Union | Germany | Great Britain (United Kingdom) | ISO | Japan | China | |||||||||
| Standard | Note (UNS) | Standard | Steel Name (Steel Number) | Standard | Class (Steel Number) | Standard | Class (Steel Number) | Standard | Note | Standard | Note | Standard | Note | ||
| AISI, SAE, ASTM |
304 (UNS S30400) |
EN 10088-2; EN 10088-3 |
X5CrNi18-10 (1.4301) | DIN EN 10088-2; DIN 17440 |
X5CrNi18-10 (1.4301) | BS EN 10088-2; BS970:1996 |
X5CrNi18-10 (1.4301); 304S15, 304S31 |
ISO 15510 | X5CrNi18-10 | JIS G4304 | SUS304 | GB/T 1220; GB/T 3280 |
06Cr19Ni10; 0Cr18Ni9 (old designation) |
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Related material: Stainless steel AISI 303, EN 1.4034 (X46Cr13), SS 410, Duplex 2205, SS904L
