Introduction of Stainless Steel 904L:
Stainless Steel 904L is a kind of austenitic stainless steel with a very low content of carbon. It is specially designed for severe conditions of corrosion and originally developed for anti-corrosion in dilute sulfuric acid. 904L which is the same as other CrNi based commonly used austenitic stainless steel has good resistance to pitting corrosion, crevice corrosion and high resistance to stress corrosion cracking, intergranular corrosion. And it offers excellent processability and weldability.
Other terms for 904L according to different standards:
Firstly, let us see the composition of this material:
|Mechanical properties||Density||Melting Point|
|Tensile Strength (MPa) min 490||Yield Strength|
0.2% proof (MPa) min 220
(% in 50mm)min 36
- Corrosion resistance
From the above tables, we can see 904L has 23~28% nickel and 4~5% molybdenum which provide it good chloride stress corrosion cracking resistance, pitting, and general corrosion resistance.
And by adding copper in it, 904L is resistant to sulphuric acid and other agents in both aggressive and mild conditions.
- Processability and weldability
904L can be easily processed and easily welded by most standard processes. It is quite soft and forms easily. But compared with conventional stainless steel such as 304L/304, its extra molybdenum and nitrogen means more powerful processing equipment may be required. This material does not require pre-heat and post-weld heat treatments.
When referring to hot forming, the working temperature of 850~1150℃ is recommended. And subsequent annealing is not required for most cases which is unlike other stainless steel.
But it should be solution annealed at 1060~1140℃.
904L is a versatile material that can be used in many industrial applications:
- Petroleum and petrochemical equipment such as reactors in these types of equipment.
- Storage and transportation equipment for sulfuric acid such as heat exchangers.
- Fuel gas desulfurization device of the power plant.
- Scrubber and fan in the organic acid treatment system.
- Pulp and paper processing industries.
- Seawater cooling devices.
- Wiring in electrostatic precipitators.
Comparison of some possible alternative material:
As 904L contains high amounts of molybdenum and nickel which are really expensive, Now most of applications require 904L are replaced by another low-cost stainless steel.
S316L is an alternative material with lower cost but it is lower resistant to corrosion.
6Mo/ 254Smo/S31254 is another alternative material which can provide higher resistance to pitting and crevice corrosion.
2205/ S31803 has a similar resistance to corrosion with 904L but with higher mechanical strength while lower cost. Only take note that it’s not suitable for temperatures above 300℃.
Super duplex can provide higher corrosion resistance and higher mechanical strength compared with 904L.