Grade 904L stainless steel is a non-stabilized austenitic stainless
steel with low carbon content. This high alloy stainless steel is
added with copper to improve its resistance to strong reducing
acids, such as sulphuric acid. The steel is also resistant to
stress corrosion cracking and crevice corrosion. Grade 904L is
non-magnetic, and offers excellent formability, toughness and
weldability.
Grade 904L contains high amounts of expensive ingredients, such as
molybdenum and nickel. Today, most of the applications that employ
grade 904L are replaced by low-cost duplex stainless steel 2205.
Key Properties
The following sections describe the properties of flat rolled
products in ASTM B625. The specifications may not be identical for
other products such as bar, tube and pipe.
Composition
The table below provides the compositional ranges of grade 904L
stainless steels:
Table 1. Composition ranges of grade 904L stainless steels
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni | Cu |
| 904L | min. max. | - 0.02 | - 2 | - 1 | - 0.045 | - 0.035 | 19 23 | 4 5 | 23 28 | 1 2 |
Mechanical Properties
The typical mechanical properties of grade 904L stainless steels
are given in the table below:
Table 2. Mechanical properties of grade 904L stainless steels
| Grade | Tensile Strength (MPa) min | Yield Strength 0.2% Proof (MPa) min | Elongation (% in 50mm) min | Hardness |
| Rockwell B (HR B) | Brinell (HB) |
| 904L | 490 | 220 | 36 | 70-90 typical | 150 |
Physical Properties
The physical properties of grade 904L stainless steels are
tabulated below:
Table 3. Typical physical properties of grade 904L stainless steels
| Grade | Density
(kg/m3) | Elastic Modulus
(GPa) | Mean Co-eff of Thermal Expansion (µm/m/°C) | Thermal Conductivity
(W/m.K) | Specific Heat 0-100°C
(J/kg.K) | Elec Resistivity
(nΩ.m) |
| 0-100°C | 0-315°C | 0-538°C | At 20°C | At 500°C |
| 904L | 7900 | 190 | 15 | - | - | 11.5 | - | 500 | 952 |
Grade Specification Comparison
The following table outlines the approximate grade comparisons of
904L stainless steels:
Table 4. Grade specifications of grade 904L stainless steels
| Grade | UNS No | Old British | Euronorm | Swedish SS | Japanese JIS |
| BS | En | No | Name |
| 904L | N08904 | 904S13 | - | 1.4539 | X1NiCrMoCuN25-20-5 | 2562 | - |
Possible Alternative Grades
The suitable alternatives to 904L stainless steels are tabulated
below:
Table 5. Possible alternative grades to grade 904L stainless steels
| Grade | Reasons for choosing grade 904L |
| 316L | A lower cost alternative, but with much lower corrosion resistance. |
| 6Mo | A higher resistance to pitting and crevice corrosion is needed. |
| 2205 | A very similar corrosion resistance, with the 2205 having higher
mechanical strength, and at a lower cost to 904L. (2205 not
suitable for temperatures above 300°C.) |
| Super duplex | Higher corrosion resistance is needed, together with a higher
strength than 904L. |
Corrosion Resistance
Grade 904L stainless steels have excellent resistance to warm
seawater and chloride attack. The high resistance of grade 904L
against stress corrosion cracking is due to the presence of high
amounts of nickel in its composition. Moreover, the addition of
copper to these grades develops resistance to sulphuric acid and
other reducing agents in both aggressive and mild conditions.
The corrosion resistance of grade 904L is intermediate between
super austenitic grades, with 6% molybdenum content, and standard
316L austenitic grades. Grade 904L is less resistant to nitric acid
than grades 304L and 310L, which are free of molybdenum. This steel
grade needs to be solution treated following cold working, to
achieve maximum stress corrosion cracking resistance under critical
environments.
Heat Resistance
Grade 904L stainless steels offer good oxidation resistance.
However, the structural stability of this grade collapses at high
temperatures, particularly above 400°C.
Heat Treatment
Grade 904L stainless steels can be solution heat-treated at 1090 to
1175°C, following by rapid cooling. Thermal treatment is suitable
for hardening these grades.
Welding
Welding of grade 904L stainless steels can be performed using all
conventional methods. This grade does not require pre-heat and
post-weld heat treatments. Grade 904L can be subjected to hot
cracking in constrained weldment. Grade 904L electrodes and rods
are used for welding grade 904L steels according to AS 1554.6.
Fabrication
Grade 904L stainless steels are high purity steels with low sulphur
content. They can be machined using any standard methods. These
grades can be readily bent to a small radius under cold conditions.
Although subsequent annealing is not required in most cases, it
should be carried out when the fabrication is performed under
severe stress corrosion cracking conditions.
Applications
Some of the major applications of grade 904L stainless steels
include:
- Wiring in electrostatic precipitators
- Oil refinery components
- Seawater cooling devices
- Gas scrubbing plants
- Pulp and paper processing industries
- Acetic, phosphoric and sulphuric acid processing plants
