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 non-magnetic under annealing conditions, but after cold working (such as stamping, stretching, bending, rolling), part of the austenite structure may be converted into martensite and therefore weakly magnetic. Type 304 has good resistance to atmospheric corrosion and oxidation. The high nickel-chromium alloy content gives it excellent corrosion resistance and is widely used in the food industry as a standard food grade stainless steel.

There are several variants of 304 grade stainless steel, such as ultra-low-carbon version type 304L, nitrogen-containing version 304N, 304H with improved creep performance, and type 302 with higher carbon content. The second most widely used 316 grade stainless steel, compared with AISI 304, reduced chromium content, increased nickel content, and added 2-3% molybdenum. The addition of molybdenum can enhance the resistance to pitting and crevice corrosion caused by chloride. Therefore, 316 SS is widely used in marine applications.

SS 304 Stainless Steel Properties

The following tables give SS 304 stainless steel properties and specifications (datasheet) including chemical composition, physical and mechanical properties, heat treatment, corrosion resistance, machinability and machining, welding, etc.

Chemical Composition

AISI 304 stainless steel chemical composition is listed in the following table.

Type 304 Stainless Steel Composition, %
ASTM Standard AISI (UNS) C, ≤ Si, ≤ Mn, ≤ P, ≤ S, ≤ Cr Ni 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 18.0-20.0 8.0-11.0 –
ASTM 666;
SAE J405		 0.08 0.75 2.00 0.045 0.03 18.0-20.0 8.0-10.5 0.1
ASTM A313/A313M 0.08 1.00 2.00 0.045 0.03 18.0-20.0 8.0-10.5 0.1
ASTM A479/A479M 0.08 1.00 2.00 0.045 0.03 18.0-20.0 8.0-10.5 –
ASTM A314;
ASTM A580/A580M		 0.08 1.00 2.00 0.045 0.03 18.0-20.0 8.0-10.5 0.1
ASTM A473 0.08 1.00 2.00 0.045 0.03 18.0-20.0 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 –

Notes:

  • ASTM A240/A240M: Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications
  • ASTM A276/A276M: Stainless Steel Bars and Shapes
  • 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 Specifying Harmonized Standard Grade Compositions for Wrought Stainless Steels
  • SAE J405: Chemical Composition of SAE Wrought Stainless Steels

Physical Properties

SS 304 stainless steel physical properties are listed in the table below such as density, melting point, specific heat, electrical resistivity, elastic modulus (modulus of elasticity), thermal conductivity, and coefficient of thermal expansion (CTE).

Notes:

  • 10-6·K-1 = 10-6/K
  • 1 Ω·mm²/m = 1 μΩ·m
  • 1 g/cm3 = 1 kg/dm3 = 1000 kg/m3
  • 1 GPa = 1 kN/mm2
  • 1 MPa = 1 N/mm2
Type 304 Stainless Steel Physical Properties
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 (106 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)

AISI 304 Stainless Steel Mechanical Properties

AISI 304 stainless steel mechanical properties are given in the datasheet below including tensile strength, yield strength, elongation, reduction in area, Brinell and Rockwell hardness, etc.

Data are from professional, authoritative and trustworthy ASTM standards.

ASTM A276 Type 304 Stainless Steel Mechanical Properties
ASTM AISI (UNS) Tensile Strength, Mpa (ksi), ≥ 0.2% Yield Strength, Mpa (ksi), ≥ Elongation in 2 in. (50 mm), %, ≥ Reduction of Area, %, ≥ 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, Dia ≤ 1/2 in (12.7mm)
515 (75) 205 (30) 30 40 Annealed, Cold finished, Dia > 1/2 in (12.7mm)
ASTM A240 Type 304 Steel Mechanical Properties
ASTM AISI (UNS) Tensile Strength, Mpa (ksi), ≥ 0.2% Yield Strength, Mpa (ksi), ≥ Elongation in 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 in 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 (Half Hard) 1035 (150) 760 (110) 6 (<0.015 in);
7 (≥ 0.015 in)
1/4 (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)
ASTM A313 Type 304 Stainless Steel Spring Wire Tensile Strength Requirements
Diameter (d), in. Diameter (d), mm Bend Test, Minimum Number of Bends ksi MPa
≤0.009 ≤0.23 – 325-355 2240-2450
0.009<d≤0.010 0.23<d≤0.25 – 320-350 2205-2415
0.010<d≤0.011 0.25<d≤0.28 – 318-348 2190-2400
0.011<d≤0.012 0.28<d≤0.30 – 316-346 2180-2385
0.012<d≤0.013 0.30<d≤0.33 – 314-344 2165-2370
0.013<d≤0.014 0.33<d≤0.36 – 312-342 2150-2360
0.014<d≤0.015 0.36<d≤0.38 – 310-340 2135-2345
0.015<d≤0.016 0.38<d≤0.41 – 308-338 2125-2330
0.016<d≤0.017 0.41<d≤0.43 – 306-336 2110-2315
0.017<d≤0.018 0.43<d≤0.46 – 304-334 2095-2300
0.018<d≤0.020 0.46<d≤0.51 – 300-330 2070-2275
0.020<d≤0.022 0.51<d≤0.56 – 296-326 2040-2250
0.022<d≤0.024 0.56<d≤0.61 – 292-322 2015-2220
0.024<d≤0.026 0.61<d≤0.66 – 291-320 2005-2205
0.026<d≤0.028 0.66<d≤0.71 8 289-318 1995-2190
0.028<d≤0.031 0.71<d≤0.79 8 285-315 1965-2170
0.031<d≤0.034 0.79<d≤0.86 8 282-310 1945-2135
0.034<d≤0.037 0.86<d≤0.94 8 280-308 1930-2125
0.037<d≤0.041 0.94<d≤1.04 8 275-304 1895-2095
0.041<d≤0.045 1.04<d≤1.14 8 272-300 1875-2070
0.045<d≤0.050 1.14<d≤1.27 8 267-295 1840-2035
0.050<d≤0.054 1.27<d≤1.37 8 265-293 1825-2020
0.054<d≤0.058 1.37<d≤1.47 7 261-289 1800-1990
0.058<d≤0.063 1.47<d≤1.60 7 258-285 1780-1965
0.063<d≤0.070 1.60<d≤1.78 7 252-281 1735-1935
0.070<d≤0.075 1.78<d≤1.90 7 250-278 1725-1915
0.075<d≤0.080 1.90<d≤2.03 7 246-275 1695-1895
0.080<d≤0.087 2.03<d≤2.21 7 242-271 1670-1870
0.087<d≤0.095 2.21<d≤2.41 7 238-268 1640-1850
0.095<d≤0.105 2.41<d≤2.67 5 232-262 1600-1805
0.105<d≤0.115 2.67<d≤2.92 5 227-257 1565-1770
0.115<d≤0.125 2.92<d≤3.17 5 222-253 1530-1745
0.125<d≤0.135 3.17<d≤3.43 3 217-248 1495-1710
0.135<d≤0.148 3.43<d≤3.76 3 210-241 1450-1660
0.148<d≤0.162 3.76<d≤4.11 3 205-235 1415-1620
0.162<d≤0.177 4.11<d≤4.50 3 198-228 1365-1570
0.177<d≤0.192 4.50<d≤4.88 1 194-225 1335-1550
0.192<d≤0.207 4.88<d≤5.26 1 188-220 1295-1515
0.207<d≤0.225 5.26<d≤5.72 1 182-214 1255-1475
0.225<d≤0.250 5.72<d≤6.35 1 175-205 1205-1415
0.250<d≤0.278 6.35<d≤7.06 1 168-198 1160-1365
0.278<d≤0.306 7.06<d≤7.77 1 161-192 1110-1325
0.306<d≤0.331 7.77<d≤8.41 1 155186 1070-1280
0.331<d≤0.362 8.41<d≤9.19 1 150-180 1035-1240
0.362<d≤0.394 9.19<d≤10.00 1 145-175 1000-1205
0.394<d≤0.438 10.00<d≤11.12 1 140-170 965-1170
0.438<d≤0.500 11.12<d≤12.70 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.
ASTM A473 Type 304 Mechanical Properties
ASTM AISI (UNS) Tensile Strength, Mpa (ksi), ≥ 0.2% Yield Strength, Mpa (ksi), ≥ Elongation in 2 in. (50 mm), %, ≥ Reduction of Area, %, ≥ Sections Conditions
ASTM A473/A473M 304 (UNS S30400) 515 (75) 205 (30) 40 50 ≤ 5 in. (127 mm) Annealed
485 (70) > 5 in. (127 mm) Annealed
ASTM A479 Type 304 Mechanical Properties
ASTM AISI (UNS) Tensile Strength, Mpa (ksi), ≥ 0.2% Yield Strength, Mpa (ksi), ≥ Elongation in 2 in. (50 mm), %, ≥ Reduction of Area, %, ≥ 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), ≥ Elongation in 2 in. (50 mm), %, ≥ Reduction of Area, %, ≥ Conditions
ASTM A580/A580M SS 304 (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, because they will not change their crystal lattice structure when heated, so they can only be hardened by cold working. Cold working will transform a part of austenite into martensite. As the amount of martensite in the 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 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 will not rust. But it’s not resistant to halide (such as chloride, fluoride, etc.) corrosion, because the halide can easily penetrate the passive film and make stainless steel lose the resistance.

Welding of AISI 304 Grade Stainless Steel

Type 304 stainless steel has excellent weldability and does not require preheating. Generally, post-weld heat treatment is not required, unless large cross-sections are welded, or weld decay may occor.

To prevent weld decay, please refer to heat treatment-stress relief, or recommend the use of ultra-low carbon stainless steel such as 304L, or stabilized stainless steel 321, 347.