Stainless Steel 316L vs 904L – What’s the Difference

Stainless steel 316L vs 904L is widely used in the industrial sector due to its cost-effectiveness and general properties such as corrosion resistance. Specifically, 904L is best suited for use in harsh environments due to its acid resistance. Whereas 316L is used in chlorine environments. In this article, you will be helped to choose the right material between 316L and 904L by understanding the differences between 316L and 904L composition, properties, and applications.

316L Stainless Steel Definition and Types

UNS S31603 stainless steel is also known as austenitic stainless steel with a low carbon content. AISI 316 L consists of chromium (16-18%), molybdenum (2-3%), and nickel (10-12%). 316L is resistant to corrosion from chlorine environments and reducing acids of the sulfuric acid type due to the presence of molybdenum. Due to the low carbon content, UNS S31603 is softer and more ductile, making 316L easier to machine than other stainless steel grades.

904L Stainless Steel Definition and Types

Austenitic stainless steel containing high alloying elements is called 904L. It has high corrosion resistance to harsh and severe corrosive environments. Other names for 904L include:

• UNS N08904
• ISO 904L
• EN 1.4539
• AISI 904L
• SUS 904L
• SS2562

Stainless Steel 316L vs 904L – What’s the Difference

Applications of Stainless Steel 316L vs 904L

316L Stainless Steel:

316L, also known as austenitic stainless steel, has high corrosion resistance in chlorine environments. 316 is biocompatible and can be cleaned and sterilized. 316L also has efficient heat transfer properties and is durable, which is why it is used in a wide range of applications listed below.

• Marine Hardware
• Chemical processing equipment parts
• Medical implants
• Pharmaceutical equipment
• Heat exchangers
• Valve and pump parts
• Springs

904L Stainless Steel:

904 L is also used in cooling systems and heat exchangers in Marin due to its good corrosion resistance in harsh environments, especially acidic environments. All these characteristics make 904 L suitable for the applications listed below.

• Oil and gas industry equipment
• Pulp and paper processing equipment
• Seawater cooling units
• Wiring in electrostatic precipitators
• Chemical containers
• Gas scrubbing systems
• Heat exchangers

Advantages and Disadvantages of 316L and 904L Stainless Steel

The advantages and disadvantages of UNS S31603 and UNS N08904 are explained below:

Advantages of AISI 316 L:

• 316L is very versatile.
• Excellent corrosion resistance to chloride-rich environments such as the ocean.
• 316L is cheaper than 904L due to less alloy content.
• Better weldability compared to 904L.
• High tensile and yield strength. Less likely to suffer from stress corrosion cracking.

Disadvantages of AISI 316 L:

• Poor corrosion resistance compared to 904L in acidic media.
• Lower toughness compared to 904L.
• Cannot withstand high temperatures.

Advantages of AISI 904 L:

• Excellent corrosion resistance to reducing acids such as sulfuric acid and phosphoric acid.
• Suitable for sensitive applications due to its non-magnetic nature.
• Resistant to high temperatures.

Disadvantages of AISI 904 L:

• High cost
• Poor weldability and machinability.

Chemical Composition of Stainless Steel 316L vs 904L

The chemical composition of AISI 316 L and AISI 904L is as follows:

Corrosion Resistance of Stainless Steel 316L and 904L

While both ISO 316L and ISO 904L perform well in corrosive environments, 904L is highly resistant to corrosion in high chloride environments. 316L is highly recommended for corrosion-resistant applications, but only for general use. 904L is used in specific severe conditions such as heat exchangers. 904L is more susceptible to stress corrosion cracking when tensile loads are applied in severe environments than 316L.

Physical Properties of Stainless Steel 316L and 904L

The table below gives a numerical comparison of 316L and 904L stainless steel.

Mechanical Properties of Stainless Steel 316L and 904L

The mechanical properties of a stainless steel grade determine its suitability for application under specific conditions. The mechanical properties of stainless steel grades ISO 316L and ISO 904L are described below:

Hardness of Stainless Steel 316L and 904L

The Brinell, Vickers, and Rockwell hardnesses of stainless steel grades ISO 316L and ISO 904L are shown in the table below.

Strength of Stainless Steel 316L and 904L

The strength of 316L and 904L is shown in the following table:

Weldability and Machinability

Among the stainless steel grades ISO 316L and ISO 904L, 904L is ductile and easy to weld and machine compared to 316L. 316L contains alloying elements compared to 904L, which makes it difficult to weld and machine.

Surface Treatment and Finishing

316L and 904L stainless steel surfaces are subjected to surface treatments such as polishing, electropolishing, and passivation. 316L has a better surface finish compared to 904L.

Heat Treatment

Both stainless steel grades ISO 316L and ISO 904L can be annealed to eliminate internal stresses and improve ductility. 316L can be annealed at 1010 – 1120°C, while 904L can be annealed at 1095 – 1175°C.

In Conclusion

The following table explains the differences between UNS S31603 and UNS N08904.