Introduction of 904L Stainless Steel

904L stainless steel is a low carbon high nickel, high molybdenum austenitic stainless steel. Excellent corrosion resistance. It has good corrosion resistance in non-oxidizing acids such as sulfuric acid, acetic acid, formic acid, and phosphoric acid. It has good pitting corrosion resistance in neutral chloride-containing media and has good resistance Crevice corrosion and stress corrosion resistance.

It is suitable for various concentrations of sulfuric acid below 70°C, and has good corrosion resistance in acetic acid at any concentration and at any temperature and mixed acid of formic acid and acetic acid under normal pressure.

---

Grades

• American Standard: UNS N08904
• European standard: 1.4539
• C standard: 00Cr20Ni25Mo4.5Cu

---

Chemical Composition of 904L
S≤	Si<≤	Mn≤	P≤	S≤	Cr≥	Ni≥	Mo≥	Cu≤	Fe
0. 02	1. 00	2. 00	0. 045	0. 035	19.00-23.00	23.00-23.00	4. 00-5. 00	1. 00-2. 00	the rest

---

Processing performance of 904L

904L has good workability and weldability.

Workability: The maximum heating temperature during hot forging can reach 1180 degrees Celsius, and the minimum stop forging temperature is not less than 900 degrees Celsius. The hot forming of this steel can be carried out at 1000-1150 degrees Celsius. The heat treatment process of the steel is 1100–1150 degrees Celsius, and it is quickly cooled after heating.

Weldability: Although this steel can be welded by a general welding process, the most appropriate welding method is manual arc welding and argon tungsten arc welding. When manual arc welding is used to weld plates no larger than 6 mm, the electrode diameter is no more than 2.5 mm; when the plate thickness is greater than 6 mm, the electrode diameter is less than 3.2 mm.

When heat treatment is required after welding, it can be heated at 1075-1125 degrees Celsius and then quickly cooled for treatment. When using tungsten argon arc welding, the filler metal can use the same material electrode, and the weld must be pickled and passivated after welding.

---

Microstructure

904L is a completely austenitic structure. Compared with general austenitic stainless steel with high molybdenum content, 904L is not sensitive to the precipitation of ferrite and α phase.

---

Physical properties of 904L stainless steel

• Density: 8.24g/cm3
• Tensile strength: ≥520MPa
• Yield strength: ≥216MPa
• Elongation: ≥35%

---

Corrosion resistance of 904L stainless steel

Because the carbon content of 904L is very low (maximum 0.020%), there will be no carbide precipitation in the case of general heat treatment and welding. This eliminates the risk of intergranular corrosion that occurs after general heat treatment and welding. Due to the high content of chromium, nickel and molybdenum and the addition of copper, 904L can be passivated even in reducing environments such as sulfuric acid and formic acid.

The high nickel content makes it have a lower corrosion rate in the active state. In pure sulfuric acid in the concentration range of 0~98%, the operating temperature of 904L can be as high as 40 degrees Celsius. The corrosion resistance of pure phosphoric acid in the concentration range of 0-85% is very good. In the industrial phosphoric acid produced by the wet process, impurities have a strong influence on the corrosion resistance. Among all kinds of phosphoric acid, 904L has better corrosion resistance than ordinary stainless steel. Among the strong oxidizing nitric acid, 904L has lower corrosion resistance than high-alloyed steel without molybdenum. In hydrochloric acid, the use of 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 has high resistance to pitting corrosion. Its crevice corrosion resistance in chloride solution is also very good. The high nickel content of 904L reduces the corrosion rate at pits and crevices. Ordinary austenitic stainless steel may be sensitive to stress corrosion in a chloride-rich environment when the temperature is higher than 60 degrees Celsius. By increasing the nickel content of the stainless steel, this sensitivity can be reduced. Due to the high nickel content, 904L has high resistance to stress corrosion cracking in chloride solutions, concentrated hydroxide solutions and hydrogen sulfide-rich environments.

---

904L can be applied in many industrial fields:

1. Petroleum and petrochemical equipment, such as reactors in petrochemical equipment, etc.
2. Sulfuric acid storage and transportation equipment, etc.
3. Power plant flue gas desulfurization device, the main use parts are: the tower body of the absorption tower, flue, gate plate, internal parts, spray system, etc.
4. The scrubber and fan in the organic acid treatment system.
5. Sea water treatment device, sea water heat exchanger.
6. Paper industry equipment
7. Sulfuric acid, nitric acid equipment, acid making, pharmaceutical industry and other chemical equipment, pressure vessels.
8. Food equipment, centrifuges, reactors in pharmaceutical factories, etc. Soy sauce tank, cooking wine, salt tank and other food machinery.
9. Equipment and parts that are strongly corrosive to dilute sulfuric acid.

---

Posted by KAYSUNS, the stainless steel pipe and fittings supplier