AISI 304 Introduction
AISI 304 stainless steel is the most common material in stainless steel. 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 and furniture decoration industry and the food and medical industry.
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: 730 Ω·m (20℃);
- 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-1):
- 17.2 (0-100℃), linear;
- 18.4 (0-500℃), linear
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 again heated 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.
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.
Conventional austenitic stainless steels cannot be hardened by heat treatment, but can be hardened by cold rolling.
The reason why 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.
Examples of ASTM 304 stainless steel rust environment: Sea water, sea wind, salt, perspiration, etc.
SS 304 Datasheet
Type 304 Stainless Steel Chemical Composition
The composition of SS304 grade stainless steel is given in table 1.
Table-1, 304 stainless steel composition
|Chemical Composition % (≤)|
ASTM 304 Mechanical Properties
The following table shows the yield strength, tensile strength, elongation and hardness of ASTM 304 (ASTM A240 A240M).
Table-2, ss 304 mechanical properties
|UNS||Steel Grade||Tensile Strength (MPa) ≥||Yield Strength ≥ (MPa) at 0.2% Offset||Elongation (%, ≥50mm)||Brinell Hardness (HBW) ≤||Rockwell Hardness (HRBW) ≤|
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).
- DIN 17440 has been replaced by DIN EN 10088-2.
- Chinese stainless steel grade 0Cr18Ni9 is an old designation, and has been replaced by 06Cr19Ni10.
- ASTM A240/A240M – Standard Specification for Chromium and Chromium-Nickel SS Plate, Sheet, and Strip for Pressure Vessels and for General Applications.
- ASTM A276/A276M – Standard Specification for SS Bars and Shapes.
- GB/T 20878 :2007 – Stainless and heat resisting steels designation and chemical composition.
- EN 10088-1 :2005, List of stainless steels.
- JIS G4304 :2005 – Hot rolled stainless steel plate, steel sheet and steel strip.
- GB/T 1220: 2007 – Stainless steel bars.
- GB/T 3280 :2015 – Cold rolled stainless steel plate, steel sheet and steel strip.
|AISI 304 equivalent|
|Standard||Grade (UNS)||Standard||Grade||Standard||Grade (Steel Number)||Standard||Grade (Steel Number)||Standard||Grade (Steel Number)||Standard||Grade||Standard||Grade||Standard||Grade|
|EN 10088-1||X5CrNi18-10||DIN EN 10088-1;|
|X5CrNi18-10 (1.4301)||DIN EN 10088-1;|
|NF EN 10088-1;||X5CrNi18-10 (1.4301)||ISO 15510||X5CrNi18-10||JIS G4304||SUS304||GB/T 20878;|
0Cr18Ni9 (Old designation)
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.