Austenitic Stainless Steel: 904L (UNS N08904)
Characteristics of 904L
UNS N08904, commonly known as 904L with its DIN equivalent W.Nr. 1.4539, is a low carbon super austenitic stainless steel. It has superior corrosion resistance to that of conventional Cr-Ni stainless steels such as SS316L and SS317L resulting from the deliberate addition of copper content. Although the 904L stainless steel has limited use with hydrochloric acids, it has high resistance to pitting corrosion in chloride solutions, high resistance to both crevice and stress-corrosion cracking. The grade is non-magnetic and has excellent formability and weldability, as well as good toughness in cryogenic temperatures. 904L stainless steels have greater resistance to precipitation of ferrite and sigma phases on cooling and welding. The low carbon content reduces the risk of intercrystalline corrosion on cooling or welding processes. This super austenitic stainless steel is widely used in chemical processing, oil & gas, and pharmaceutical industries.
The 904L is designed for environments with severe corrosion conditions. The alloy was originally developed to resist corrosion in dilute sulfuric acid. This feature has been proved to be very successful in practical application for many years. Now 904L has been standardized in many countries, and has been approved to be used in the manufacture of pressure vessels. Like other CrNi austenitic steels, 904L alloy has good resistance to spot corrosion and crevice corrosion, high resistance to stress corrosion cracking, good resistance to intergranular corrosion, good machinability and weldability. During hot forging, the maximum heating temperature can reach 1180 ℃, and the minimum stop forging temperature is not less than 900 ℃. The hot forming of this steel can be carried out at 1000-1150 ℃. The heat treatment process of the steel is 1100-1150 ℃, and it can be quickly cooled after heating. Although this steel can be welded by general welding process, the most appropriate welding method is manual arc welding and TIG welding. The diameter of electrode shall not be greater than 2.5mm when manual arc welding is adopted for plates with a thickness of no more than 6mm; the diameter of electrode shall be less than 3.2mm when plate thickness is greater than 6mm. When post welding heat treatment is required, it can be heated at 1075-1125 ℃ and then cooled quickly. The filler metal during TIG welding can be used as the same material electrode, and the weld must be pickled and passivated after welding.
Metallographic structure of 904L
904L is a complete austenitic structure. Compared with austenitic stainless steel with high molybdenum content, 904L is not sensitive to the precipitation of ferrite and α phase.
Grade specifications of grade 904L
| GB/T | UNS | AISI/ASTM | ID | W.Nr |
| 00Cr20Ni25Mo4.5Cu | N08904 | 904L | F904L | 1.4539 |
ASTM A312 UNS N08904 seamless pipes, 12.7mmx1.25mmx6m.
Chemical Composition of 904L
| The Chemical Composition of 904L, % | |
|---|---|
| C | ≤0.020 |
| Mn | ≤2.00 |
| P | ≤0.045 |
| S | ≤0.035 |
| Si | ≤1.00 |
| Cr | 19.0-23.0 |
| Ni | 23.0-28.0 |
| Mo | 4.0-5.0 |
| N | ≤0.10 |
| Cu | 1.0-2.0 |
As the carbon content of 904L is very low (0.020% at most), there will be no carbide precipitation under the condition of general heat treatment and welding. This eliminates the risk of intergranular corrosion after general heat treatment and welding. Because of the high content of Cr, Ni, Mo and the addition of Cu, 904L can be passivated even in reducing environment, such as sulfuric acid and formic acid. The high content of nickel makes the corrosion rate lower in the active state. In the concentration range of 0 ~ 98%, the temperature of 904L can reach 40 ℃. In the concentration range of 0 ~ 85% pure phosphoric acid, its corrosion resistance is very good. In industrial phosphoric acid produced by wet process, impurities have a strong influence on corrosion resistance. Among all kinds of phosphoric acid, 904L is superior to ordinary stainless steel in corrosion resistance. In the strong oxidizing nitric acid, 904L has lower corrosion resistance than the high alloy steel without molybdenum. In hydrochloric acid, 904L is limited to a lower concentration of 1-2%. In this concentration range. The corrosion resistance of 904L is better than that of conventional stainless steel. 904L steel has high resistance to spot corrosion. In chloride solution, it has good resistance to crevice corrosion. The high nickel content of 904L reduced the corrosion rate in pits and crevices. When the temperature of ordinary austenitic stainless steel is higher than 60 ℃, it may be sensitive to stress corrosion in a chloride rich environment. Due to the high nickel content, 904L has a high resistance to stress corrosion cracking in chloride solution, concentrated hydroxide solution and hydrogen sulfide rich environment.
Mechanical Properties of 904L
| Tensile Strength, min. | Yield Strength, min. | Elongation, min. | ||
|---|---|---|---|---|
| ksi | Mpa | ksi | Mpa | % |
| 71 | 490 | 31 | 220 | 35 |
Density: 8.0g/cm3. Tensile strength: σ B ≥ 520mpa. Elongation: δ ≥ 35%
Physical Properties of 904L
ASTM A276 (UNS N08904) 904L round bars, Φ70mm.
| Density | Specific Heat | Thermal Conductivity | Thermal Expansion | Modulus Elasticity | Electrical Resistivity |
|---|---|---|---|---|---|
| g/cm3 | J/(kg*K) | W/(m*k) | mm/m/°C | Gpa | µohm/cm |
| 7.95 | 450 | 11.5 | 15.8 | 190 | 9.52 |
Product Forms and Relative Standards
| Product Form | Standard |
|---|---|
| 904L plates, 904L sheets & strips | ASATM A240, A480 |
| 904L bars, 904L rods, 904L billets | ASTM A276, A479 |
| Forging (904L flanges, 904L pipe fittings, 904L Baffle, F904L Forged Ring, 904L Tube Sheet) | ASTM A182, A484 |
| 904L welded and seamless pipes/ Tubes | ASTM A312, A269 |
| 904L butt welding pipe fittings | ASTM A403, ASME B16.9 |
Stress corrosion resistance of 904L
|
Grade |
Test medium |
Time of occurrence of stress corrosion crack, h |
|
00Cr18Ni10 |
40%CaCl2,Boiling temperature |
<12 |
|
00Cr18Ni13Mo2 |
The same as above |
<12 |
|
904L |
The same as above |
1000, stress free corrosion |
|
00Cr18Ni10 |
25%NaCl+1%K2Cr2O7, pH=5, boiling |
<20 |
|
00Cr18Ni13Mo2 |
The same as above |
<321 |
|
904L |
The same as above |
1000, stress free corrosion |
As the carbon content of 904L is very low (0.020% at most), there will be no carbide precipitation under the condition of general heat treatment and welding. This eliminates the risk of intergranular corrosion after general heat treatment and welding. Because of the high content of Cr, Ni, Mo and the addition of Cu, 904L can be passivated even in reducing environment, such as sulfuric acid and formic acid. The high content of nickel makes the corrosion rate lower in the active state. In the concentration range of 0 ~ 98%, the temperature of 904L can reach 40 ℃. In the concentration range of 0 ~ 85% pure phosphoric acid, its corrosion resistance is very good. In industrial phosphoric acid produced by wet process, impurities have a strong influence on corrosion resistance. Among all kinds of phosphoric acid, 904L is superior to ordinary stainless steel in corrosion resistance. In the strong oxidizing nitric acid, 904L has lower corrosion resistance than the high alloy steel without molybdenum. In hydrochloric acid, 904L is limited to a lower concentration of 1-2%. In this concentration range. The corrosion resistance of 904L is better than that of conventional stainless steel. 904L steel has high resistance to spot corrosion. In chloride solution, it has good resistance to crevice corrosion. The high nickel content of 904L reduced the corrosion rate in pits and crevices. When the temperature of ordinary austenitic stainless steel is higher than 60 ℃, it may be sensitive to stress corrosion in a chloride rich environment. Due to the high nickel content, 904L has a high resistance to stress corrosion cracking in chloride solution, concentrated hydroxide solution and hydrogen sulfide rich environment.
Processing performance of 904L
Weldability
Like general stainless steel, 904L can be welded in a variety of ways. The most commonly used welding method is manual arc welding or Sui Xing gas shielded welding. The welding rod or wire metal is based on the composition and purity of the base metal, and the content of molybdenum is higher than that of the base metal. Preheating is generally not required before welding, but in cold outdoor operation, in order to avoid condensation of water vapor, the joint or adjacent area can be heated evenly. Note that the local temperature should not exceed 100 ℃, so as not to cause carbon accumulation and intergranular corrosion. Small linear energy, continuous and fast welding rate should be adopted during welding. Generally, no heat treatment is required after welding. If heat treatment is required, it shall be heated to 110 ~ 1150 ℃ and then cooled rapidly.
Supporting welding materials: welding rod (E385-16/17), welding wire (ER385).
Machining performance
The machining characteristics of 904L are similar to other austenitic stainless steels, and there is a trend of tool sticking and work hardening in the process of machining. It is necessary to use positive rake angle cemented carbide tools and use vulcanized and chlorinated oil as cutting coolant. The equipment and process shall be based on the premise of reducing work hardening. Slow cutting speed and feed amount should be avoided in the cutting process.
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.
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.
Application of 904L
904L alloy is a multi-purpose material, which can be applied in many industrial fields:
- Petroleum and petrochemical equipment, such as reactors in petrochemical equipment.
- Sulfuric acid storage and transportation equipment, such as heat exchanger, transportation pipeline, etc.
- The main parts of FGD device in power plant are: tube sheet, absorber body, flue, baffle, internals, spray system, etc.
- Scrubber and fan in organic acid treatment system.
Source: China 904L Pipe Fittings Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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- Nickel Alloy: Hastelloy C-276 (UNS N10276)
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