SS 304 Grade AISI 304 Stainless Steel SS304 Properties, Composition

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ASTM SAE AISI 304 stainless steel pipe fitting SS304 SS 304 Type

AISI 304 Grade Stainless Steel

AISI 304 stainless steel is the most commonly used material in stainless steels, and is usually purchased in an annealed or cold worked state. Because SS 304 contains 18% chromium (Cr) and 8% nickel (Ni), it is also known as 18/8 stainless steel. SS304 has good processability, weldability, corrosion resistance, heat resistance, low temperature strength and mechanical properties, good hot workability such as stamping and bending, and no heat treatment hardening. SS304 is widely used in the industrial use, furniture decoration, food and medical industry, etc.

AISI 304L is the low carbon version of 304, AISI 316 is better than grade 304 in certain properties, corrosion resistance and heat resistance, etc. For more information, please check 304 vs 316 stainless steel.

SS 304 Datasheet & Specification

The datasheet and specification are summarized in the following tables including chemical composition and properties.

Type 304 Stainless Steel Chemical Composition

The composition of SS304 grade stainless steel is given in table 1.

Table-1, AISI 304 stainless steel composition

Chemical Composition % (≤)
ASTMAISI (UNS)CSiMnPSCrNiNProduct
ASTM A240/A240MSS 304 (S30400)0.070.752.000.0450.0317.5-19.58.0-10.50.10Plate, Sheet, and Strip
ASTM A276A/276M0.081.002.000.0450.03018.0-20.08.0-11.0Bars and Shapes

SS 304 Stainless Steel Properties

The following table shows SS304 properties including mechanical properties and physical properties.

Table-2, SS 304 Mechanical Properties

The tables below list SS304 material mechanical properties including yield strength, tensile strength, elongation and hardness, etc.

SS 304 Mechanical Properties, data are for 25.4 mm (1 in.) diameter bar
Steel (UNS)Tensile strength (MPa)Yield strength (MPa)Elongation in 50 mm (%)Reduction in area (%)Hardness (HB)Condition
AISI 304 (S30400)5852356070149Annealed bar
69041545212Annealed and cold drawn
86065525275Cold drawn high tensile
ASTMAISI (UNS)Tensile Strength (MPa) ≥Yield Strength  ≥ (MPa) at 0.2% OffsetElongation in 50 mm (%, ≥)Reduction of Area, %, ≥Brinell Hardness (HBW) ≤Rockwell Hardness (HRBW)  ≤ProductConditions
ASTM A240/A240M304 (S30400)5152054020192Plate, Sheet, and Strip
ASTM A276A/276M5152054050Bars and ShapesHot finished
6203103040Cold finished, Dia ≤ 12.7mm
5152053040Cold finished, Dia > 12.7mm

SS 304 Physical Properties

  • The density of 304 stainless steel: 7.93 g/cm3;
  • Melting point: 1398-1454 ℃;
  • Specific heat capacity: 500 J/(Kg·K) at 0-100℃;
  • Electrical resistivity: 0.73 μΩ·m (20℃);
  • Magnetic permeability: 1.02 (Approximate)
  • Elastic modulus: 193 GPa (28×106 psi)
  • Thermal diffusivity: 3.84 mm2/s (from 20 to 100 ℃)
  • Thermal conductivity of stainless steel 304 (W/m·K):
    • 16.3 (100 ℃);
    • 21.5 (500 ℃)
  • Coefficient of thermal expansion 304 stainless steel (10-6/K):
    • 17.2 (0-100℃),
    • 17.8 (0-300℃),
    • 18.4 (0-500℃),

Magnetic Properties

Type 304 steel is not magnetic, but may be slightly magnetic after cold working.

Heat Resistance

Sensitization occurs when austenitic stainless steel is heated between 425 and 815 °C. Carbon and chromium combine to form chromium carbide, which precipitates at the crystal boundary, so the Cr content near the grain boundary is greatly reduced, and becomes a Cr-depleted region. Therefore, its corrosion resistance is lowered.

In order to prevent sensitization, the following methods can be used:

  • Rapidly passing the sensitized temperature range (425-815°C), thus Cr does not have enough time to combine with C, and it is impossible to precipitate chromium carbide.
  • The sensitized stainless steel is reheated to a temperature (1040 to 1065 ° C) sufficient to decompose the chromium carbide, and then rapidly cooled (water quenching if possible) to make the chromium carbide less likely to precipitate.
  • Use ultra-low carbon austenitic stainless steels, such as 304L and 316L, can reduce the formation of chromium carbide and reduce the probability of chromium-depleted envelope.

Heat Treatment

Solution Treatment (Annealing)

The solution annealing temperature range is 1010-1065 ℃ (1040 °C is recommended) and then rapidly cooled.

Before annealing, the surface of the stainless steel should be carefully cleaned, and to prevent the formation of an oxide layer during the annealing process, vacuum, hydrogen or inert gas protection must be used.

Forging

Typical forging temperature is 925-1260 ℃ (1700-2300 ℉).

Hardening

AISI SAE ASTM 304 can’t be hardened by heat treatment but can be hardened by cold working.

Stress Relieving

When the weldment is not suitable for full annealing, the residual stress can be moderately reduced below 600 °C.

Cold Working

SS304 is suitable for cold working operations including cold heading, cold drawing, cold extrusion and cold riveting, but it is more difficult than cold working of carbon steel.

Machining

SS304 is more difficult to machine than carbon steel and low alloy steel because of its higher strength and higher work hardening rate. Therefore, more power and lower processing speed are required, resulting in shortened tool life and difficulty in obtaining a smooth surface.

Welding

SS 304 has excellent welding performance and does not require preheating, but requires similar filler material composition but high alloy content. Ensure that the weld contains 5-10% ferrite during welding to avoid cracking of the weld. Reduce the carbon content, such as using 304L, stabilized stainless, or adding niobium (Nb), to avoid weld corrosion. SS 304 may require subsequent reannealing after soldering or heat treatment to achieve optimum corrosion resistance, softness and ductility. Because intergranular corrosive chromium carbide is dissolved during the annealing process.

Postweld heat treatment: 949-1149 °C (1740-2100 °F) if undertaken, or stress relieve below 649 °C (1200 °F) to avoid weld corrosion.

Corrosion Resistance

The reason why AISI 304 grade stainless steel has excellent corrosion resistance in the atmosphere is due to the formation of a chromium passivation film on its surface. But when SS304 is in a warm chloride environment, the corrosion is even faster than non-alloy mild steel. Below is the application range of stainless steel in chloride ion medium for reference.

SS 304 316 stainless steel in chloride medium

Examples of ASTM 304 stainless steel rust environment: Sea water, sea wind, salt, perspiration, etc.

Applications

AISI 304 stainless steel is widely used in petroleum & chemical industry, metallurgical machinery, aerospace industry, food processing equipment, instruments, household appliances and hardware manufacturing industries.

SS304 material is made into a great many intermediate products such as steel sheet & plate, steel tube & pipe, steel bar & flat, rod & wire, etc.

Final products such as all kinds of kitchen ware, tableware, medical device, machinery and parts, etc.

AISI 304 Equivalent Grade

ASTM type 304 stainless steel equivalent to ISO, European EN (Germany DIN, British BSi, France NF…), Japanese JIS and Chinese GB standard (For reference).

Notes:

  1. DIN 17440 has been replaced by DIN EN 10088-2.
  2. Chinese stainless steel grade 0Cr18Ni9 is an old designation, and has been replaced by the new name 06Cr19Ni10.
  3. ASTM A240/A240M – Standard Specification for Chromium and Chromium-Nickel SS Plate, Sheet, and Strip for Pressure Vessels and for General Applications.
  4. ASTM A276/A276M – Standard Specification for SS Bars and Shapes.
  5. JIS G4304 :2005 – Hot rolled stainless steel plate, steel sheet and steel strip.
  6. GB/T 1220: 2007 – Stainless steel bars.
  7. GB/T 3280 :2015 – Cold rolled stainless steel plate, steel sheet and steel strip.
AISI 304 equivalent grade
USEuropeanGermanyBritain (UK)ISOJapanChina
StandardGrade (UNS)StandardSteel Name (Steel Number)StandardGrade (Steel Number)StandardGrade (Steel Number)StandardGradeStandardGradeStandardGrade
AISI SAE;
ASTM A240/A240M;
A276/A276M
AISI 304
(S30400)
EN 10088-2;
EN 10088-3
X5CrNi18-10 (1.4301)DIN EN 10088-2;
DIN 17440
X5CrNi18-10 (1.4301)DIN EN 10088-2;
BS970 :1996
X5CrNi18-10 (1.4301);
304S15
ISO 15510X5CrNi18-10JIS G4304SUS304GB/T 1220;
GB/T 3280
06Cr19Ni10;
0Cr18Ni9 (Old designation)

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