Oct 23 2001
Grade 304 is a standard "18/8" stainless. It is the most versatile and most widely used stainless steel available, even though a wide range of alternatives are available; and has excellent forming and welding characteristics. The balanced austenitic structure of Grade 304 enables it to be severely deep drawn without intermediate annealing. This means that this grade steel is dominant in the manufacture of drawn stainless parts such as sinks, hollow-ware and saucepans. For these applications, it is common to use special "304DDQ" (Deep Drawing Quality) variants. Grade 304 can be readily braked or roll-formed into a variety of components for applications in the industrial, architectural, and transportation fields. It also has outstanding welding characteristics. Post-weld annealing is not required when welding thin sections.
.jpg)
Image Credits: Suprun Vitaly/shutterstock.com
Grade 304L, the low carbon version of 304, does not require post-weld annealing and is therefore extensively used in heavy gauge components (over about 6mm). Grade 304H with its higher carbon content is used in applications at elevated temperatures. The austenitic structure also gives these grades excellent toughness, even down to cryogenic temperatures.
Key Properties
These properties are specified for flat rolled product (plate, sheet, and coil) in ASTM A240/A240M. Similar but not necessarily identical properties are specified for other products such as pipe and bar in their respective specifications.
Composition
Table 1. Typical composition ranges for 304-grade stainless steel
| Grade |
|
C |
Mn |
Si |
P |
S |
Cr |
Mo |
Ni |
N |
| 304 |
min.
max. |
-
0.08 |
-
2.0 |
-
0.75 |
-
0.045 |
-
0.030 |
18.0
20.0 |
- |
8.0
10.5 |
-
0.10 |
| 304L |
min.
max. |
-
0.030 |
-
2.0 |
-
0.75 |
-
0.045 |
-
0.030 |
18.0
20.0 |
- |
8.0
12.0 |
-
0.10 |
| 304H |
min.
max. |
0.04
0.10 |
-
2.0 |
-
0.75 |
-0.045 |
-
0.030 |
18.0
20.0 |
- |
8.0
10.5 |
- |
Mechanical Properties
Table 2. Typical mechanical properties of 304-grade stainless steel
| Grade |
Tensile Strength (MPa) min |
Yield Strength 0.2% Proof (MPa) min |
Elongation (% in 50 mm) min |
Hardness |
| Rockwell B (HR B) max |
Brinell (HB) max |
| 304 |
515 |
205 |
40 |
92 |
201 |
| 304L |
485 |
170 |
40 |
92 |
201 |
| 304H |
515 |
205 |
40 |
92 |
201 |
304H also requires a grain size of ASTM No 7 or coarser.
Physical Properties
Table 3. Typical physical properties of 304-grade stainless steel in the annealed condition
| Grade |
Density (kg/m3) |
Elastic Modulus (GPa) |
Mean Coefficient of Thermal Expansion (μm/m/°C) |
Thermal Conductivity (W/m.K) |
Specific Heat 0-100 °C (J/kg.K) |
Electrical Resistivity (nΩ.m) |
| 0-100 °C |
0-315 °C |
0-538 °C |
at 100 °C |
at 500 °C |
| 304/L/H |
8000 |
193 |
17.2 |
17.8 |
18.4 |
16.2 |
21.5 |
500 |
720 |
Grade Specification Comparison
Table 4. Approximate Grade specifications for 304-grade stainless steel
| Grade |
UNS No |
Old British |
Euronorm |
Swedish SS |
Japanese JIS |
| BS |
En |
No |
Name |
| 304 |
S30400 |
304S31 |
58E |
1.4301 |
X5CrNi18-10 |
2332 |
SUS 304 |
| 304L |
S30403 |
304S11 |
- |
1.4306 |
X2CrNi19-11 |
2352 |
SUS 304L |
| 304H |
S30409 |
304S51 |
- |
1.4948 |
X6CrNi18-11 |
- |
- |
These comparisons are approximate only. The list is intended as a comparison of functionally similar materials, not as a schedule of contractual equivalents. If exact equivalents are needed original specifications must be consulted.
Possible Alternative Grades
Table 5. Possible alternative grades to 304-grade stainless steel
| Grade |
Why it might be chosen instead of 304 |
| 301L |
A higher work hardening rate grade is required for certain roll-formed or stretch formed components. |
| 302HQ |
Lower work hardening rate is needed for cold forging of screws, bolts, and rivets. |
| 303 |
Higher machinability needed, and the lower corrosion resistance, formability, and weldability are acceptable. |
| 316 |
Higher resistance to pitting and crevice corrosion is required, in chloride environments |
| 321 |
Better resistance to temperatures of around 600-900 °C is needed…321 has higher hot strength. |
| 3CR12 |
A lower cost is required, and the reduced corrosion resistance and resulting discoloration are acceptable. |
| 430 |
A lower cost is required, and the reduced corrosion resistance and fabrication characteristics are acceptable. |
Corrosion Resistance
Grade 304 stainless steel is excellent in a wide range of atmospheric environments and many corrosive media. It is subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above 60 °C (approximate). Grade 304 is considered to be resistant to potable water up to approximately 200 mg/L chlorides at ambient temperatures, reducing to approximately150 mg/L at 60 °C.
Heat Resistance
Grade 304 has good oxidation resistance in intermittent service to 870 °C, and in continuous service to 925 °C. Continuous use of 304 in the 425-860 °C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 304L is more resistant to carbide precipitation and can be heated into this temperature range.
Grade 304H has higher strength at elevated temperatures so is often used for structural and pressure-containing applications at temperatures above 500 °C up to about 800 °C (approximate). 304H will become sensitized in the temperature range of 425-860 °C. Whilst this is not a problem for high-temperature applications, it will result in reduced aqueous corrosion resistance.
Heat Treatment
During Solution Treatment (Annealing) Grade 304 can be heated to 1010-1120 °C and is then cooled rapidly. These grades cannot be hardened by thermal treatment.
Welding
Grade 304 has excellent weldability by all standard fusion methods, both with and without filler metals. AS 1554.6 pre-qualifies welding of 304 with Grade 308 and 304L with 308L rods or electrodes (and with their high silicon equivalents). Heavy welded sections in Grade 304 may require post-weld annealing for maximum corrosion resistance. This is not required for Grade 304L. Grade 321 may also be used as an alternative to 304 if heavy section welding is required and post-weld heat treatment is not possible.
Machining
A "Ugima" improved machinability version of grade 304 is available in bar products. "Ugima" machines significantly better than standard 304 or 304L, giving higher machining rates and lower tool wear in many operations.
Dual Certification
It is common for 304 and 304L to be stocked in "Dual Certified" form, particularly in plate and pipe. These items have chemical and mechanical properties complying with both 304 and 304L specifications. Such dual certified product does not meet 304H specifications and may be unacceptable for high-temperature applications.
Typical Applications
- Food processing equipment, particularly in beer brewing, milk processing & winemaking
- Kitchen benches, sinks, troughs, equipment and appliances
- Architectural paneling, railings & trim
- Chemical containers, including for transport
- Heat Exchangers
- Woven or welded screens for mining, quarrying & water filtration
- Threaded fasteners
- Springs
This article was updated on 19th August, 2019.