Alloy 304 is a T-300 series stainless steel austenitic, which has a minimum of 18% chromium and 8% nickel with a maximum of 0.08% carbon. It is the standard “18/8 stainless” that is commonly found in pans and cooking tools. Alloy 304 is the most versatile and widely used alloy in the stainless steel family. It may be used for a wide variety of home and commercial applications and exhibits excellent corrosion resistance, has a high ease of fabrication, outstanding formability, and tremendous strength. The austenitic stainless steels are also considered to be the most weldable of the high-alloy steels and can be welded by all fusion and resistance welding processes. Due to its controlled carbon content of 0.04 to 0.10, Alloy 304H provides improved high temperature strength when exposed to temperatures above 800oF. Alloy 304H also has greater short term and long term creep strength than Alloy 304L at temperatures above 500oC and is more resistant to sensitization than Alloy 304L.
|Yield Strength 0.2%
Offset ksi (min.)
50 mm (min.)
(Rockwell B) MAX
Thermal Expansion (min/in)-°F
|Thermal Conductivity BTU/hr-ft-°F||Specific Heat BTU/lbm -°F||Modules of Elasticity (annealed)2-psi|
|at 68 °F||at 68 – 212°F||at 68 – 1600°F||at 212°F||at 932°F||at 32 – 212°F||in tension (E)|
|0.285||9.2||11.0||9.4||12.4||0.12||29 x 106|
Alloy 304H is often used as a material of construction up to about 1500oF. Some examples of applications that Alloy 304H is commonly used for includes:
- Most commonly used in petroleum refineries
- Heat exchangers
- Cooling towers
- Steam exhausts
- Electric generation plants
- On occasion will be found in fertilizer and chemical plants
Standards – Alloy 304H
ASTM/ASME: UNS S30409
- Good oxidation resistance in intermittent service to 870O C and in continuous service to 920O C
- Continuous use of Alloy 304 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important
- Alloy 304H has higher strength at elevated temperatures so is often used for structural and pressure-containing applications at temperatures above about 500°C and up to about 800°C
- Alloy 304H will become sensitized in the temperature range of 425-860°C; this is not a problem for high temperature applications, but will result in reduced aqueous corrosion resistance.
- Resistance to corrosion in oxidizing environments is a result from the 18 to 19% chromium that the 304 alloys contain
- Resistance to moderately aggressive organic acids is a result from the 9 to 11% nickel that the 304 alloys contain
- At times, Alloy 304L may show a lower corrosion rate than the higher carbon Alloy 304; otherwise, the 304, 304L, and 304H alloys may be considered to perform uniformly in most corrosive environments.
- readily welded by most standard processes.
- may be necessary to anneal the plate after welding
- annealing helps restore corrosion resistance lost by the sensitization.
Processing – Hot Forming:
- Working tempertarues of 1652-2102 degrees F are recommended
- meterial should be annealed at 1900 degrees F
- material should be water quenched or or rapidly cooled
Processing – Cold Forming:
- alloy is quite ductile and forms easily
- helps increase strength and hardness of alloy
- may leave alloy slightly magnetic
- subject to work hardening during deformation
- subject to chip breaking
- best results achieved through slower speed, heavier feeds, good lubrication, and sharp tooling