+44 (0) 1329 843355

sales@intamet.co.uk

What is Stainless Steel 304, 304L, 304H?

These stainless steels are widely used in the petrochemical and food industries due to their corrosion resistance, tensile strength and ability to accommodate higher temperatures. There is a trade-off between corrosion resistance and temperature characteristics according to the specific grade.


Grade 304 is an austenitic steel with excellent welding and forming characteristics. The key elements in 304 are Chromium and Nickel which give it excellent resistance to corrosion.

It has good resistance to corrosion, it is malleable and ductile and has good weldability. 

The austenitic structure allows it to be deep drawn without intermediate annealing. It is also unnecessary to anneal it following welding thin sections.

It is widely used in the food industry, water, architectural, cryogenic and high-temperature applications.

Widely used for good quality cutlery where it is described as 18/8 referring to the percentages of Chromium and Nickel.

The range of properties of 304 mean that it is used in many industries.

Its resistance to corrosion makes it suitable for use in the food industry, particularly dairy, wine and beer production or processing.

Its malleability makes it easily formed into sinks, troughs and other kitchen appliances and it can be spun easily making it suitable for the production of pots and pans.

A good choice for architectural applications being less expensive than 316. Its corrosion resistance makes it an excellent choice for internal panelling or other fittings and it is also suitable for use externally when away from the marine environment. It is however not as resistant to chloride corrosion as 316 and if there is salt spray in the atmosphere it is generally best to use 316.

The combination of corrosion resistance and formability make it a good choice for chemical containers - including those used for transportation.

It has good heat resistance and is therefore widely used in heat-exchangers. Where particularly high temperatures 304H should be considered

Corrosion Resistance

304 has good corrosion resistance in a wide range of atmospheric conditions and to many corrosive media. It is however subject to pitting corrosion in chloride environments particularly in warm conditions.

It is also subject to stress corrosion cracking above 60o.

It is generally resistant to concentrations of about 200mg/litre of chlorides at 20o but this drops to about 150mg/litre at 60o.

Heat Resistance

304 is not generally regarded as a grade to be selected when very high temperatures are expected but it may have certain benefits. It resists oxidisation in continuous use up to 925o and in intermittent use to 870o. However, using it in a temperature range between 425o and 860o can result in carbide precipitation and subsequently intergranular corrosion.

304L, with its lower carbon content, is less prone to carbide precipitation and can be used at these temperatures.

304H has greater strength at high temperatures and may be the steel of choice where both high-temperature resistance and corrosion resistance are required. Thes requirements are often found in flue gas chimneys where gasses may condense forming aggressive often acidic liquids.

In common with other austenitic stainless steels, 304 grade has strong work hardening characteristics. Clearly, in some cases, this can be an advantage, but generally, it is an issue to be considered carefully.

If it is likely to be an issue, discussion with the producer can be valuable as minor variations to the precise composition and process can have benefits.

Where heavy sections have to we welded, post-weld annealing may be necessary to restore corrosion resistance.

The main constituents of 304 stainless steel - other than iron - are Chromium and Nickel.

304 contains 18 - 20% Chromium (Cr). Chromium is the essential chemical in all stainless steel and it is that which forms the thin passive layer that makes the metal "stainless"

304 also contains 8-10.5% Nickel (Ni). This is added to make the Austenitic structure more stable at normal temperatures. 

The nickel also improves high-temperature oxidation resistance makes the steel resistant to stress corrosion cracking.

Where the steel is to be stretched formed a lower percentage (8%) of nickel should be selected. If the steel is to be deep drawn a higher percentage is better (9% or more).

In addition a number of other chemicals may be present but these are expressed as maximum permited levels with the exception of the increased quantity of carbon required in 304H - i.e. a minimum of .04% and a maximum of 0.10%

GradeCMnSiPSCrMoNiN
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
-

Physical Properties

 

Metric

English

Density

8 g/cc

0.289 lb/in³

               

Mechanical Properties

Hardness, Brinell

123

123

Converted from Rockwell B hardness.

Hardness, Knoop

138

138

Converted from Rockwell B hardness.

Hardness, Rockwell B

70

70

 

Hardness, Vickers

129

129

Converted from Rockwell B hardness.

Tensile Strength, Ultimate

505 MPa

73200 psi

 

Tensile Strength, Yield

215 MPa

31200 psi

at 0.2% offset

Elongation at Break

70 %

70 %

in 50 mm

Modulus of Elasticity

193 - 200 GPa

28000 - 29000 ksi

 

Poisson's Ratio

0.29

0.29

 

Charpy Impact

325 J

240 ft-lb

 

Shear Modulus

86 GPa

12500 ksi

 

Electrical Properties

Electrical Resistivity

7.2e-005 ohm-cm

7.2e-005 ohm-cm

at 20°C (68°F); 1.16E-04 at 650°C (1200°F)

Magnetic Permeability

1.008

1.008

at RT

Thermal Properties

CTE, linear 20°C

17.3 µm/m-°C

9.61 µin/in-°F

from from 0-100°C

CTE, linear 250°C

17.8 µm/m-°C

9.89 µin/in-°F

at 0-315°C (32-600°F)

CTE, linear 500°C

18.7 µm/m-°C

10.4 µin/in-°F

at 0-650°C

Specific Heat Capacity

0.5 J/g-°C

0.12 BTU/lb-°F

from 0-100°C (32-212°F)

Thermal Conductivity

16.2 W/m-K

112 BTU-in/hr-ft²-°F

at 0-100°C, 21.5 W/m°C at 500°C

Melting Point

1400 - 1455 °C

2550 - 2650 °F

 

Solidus

1400 °C

2550 °F

 

Liquidus

1455 °C

2650 °F

 

The two main variants of grade 304 are the low carbon form 304L and the high carbon form 304H

304L has a maximum of 0.30% carbon. This reduces the tendency for carbide precipitation when welding. Carbide precipitation can result in intergranular corrosion.

304H has between 0.04 and 0.1% carbon. This gives it greater strength at high temperature but does make it more vulnerable to carbide precipitation when welding.

Since 304 has as having a maximum of 0.08% carbon, there are potential overlaps in the specifications which means that it is not uncommon to find dual specification. 

304L clearly has less than 0.08% carbon and can, therefore, be described as 304/304L.

304 may have up to 0.08% carbon so if its carbon content is between 0.04 and 0.08% carbon it can be described as 304/304H.

Stainless 304, 304H, 304L Forms Available

  • Tube
  • Pipe
  • Fittings
  • Flanges
  • Special Sections
  • Sheet
  • Plate
  • Flat Bar
  • Round Bar
  • Hollow Bar
  • Angles
  • i Beam
  • U Channel

Translate to your language