Stainless Steel 904L

Its high nickel and chromium content make it corrosion resistant in both oxidizing and reducing environments. The copper and molybdenum help to make it resistant to pitting as well as crevice corrosion. The nickel content makes it resistant to chloride SCC and the low proportion of carbon makes it resistant to inter-granular corrosion. It is considered especially well-suited to handling sulfuric acid and phosphoric acid, though at high temperatures it may be subject to stress corrosion cracking. It has good machinability and weldability and can be used in pressure vessels.

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

The high nickel content also results in 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. In pure phosphoric acid in the concentration range of 0~85%, its corrosion resistance is very good. In industrial phosphoric acid produced by the wet process, impurities have a strong effect on the corrosion resistance. 

Of all the various phosphoric acids, 904L inox is more corrosion resistant than ordinary stainless steel. In strong oxidizing nitric acid, 904L stainless steel has lower corrosion resistance than highly alloyed steel grades that do not contain molybdenum. In hydrochloric acid, the use of 904L is limited to lower concentrations 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 pitting corrosion. Its resistance to crevice corrosion in chloride solutions is also very good. The high nickel content of 904L reduces the rate of corrosion in pits and crevices. Ordinary austenitic stainless steels may be susceptible to stress corrosion in a chloride-rich environment at temperatures above 60°C, and this sensitization can be reduced by increasing the nickel content of the stainless steel. 

Due to the high nickel content, stainless steel 904L is highly resistant to stress corrosion cracking in chloride solutions, concentrated hydroxide solutions and hydrogen sulfide rich environments.

Stainless steel 904L Physical Properties

Melting point: 1300-1390 ℃
Density: 8 g/cm3

Alloy 904L (UNS N08904) Chemical Composition,%

Stainless steel 904L Mechanical Properties

Stainless Steel 904L Equivalent Grades

Stainless Steel 904L ASTM Specifications

Welding performance：
Like general stainless steel, 904 L can be welded by a variety of welding methods. The most commonly used welding methods are manual arc welding or inert gas shielded welding. The electrode or wire metal is based on the composition of the base metal and has a higher purity. The content of molybdenum is higher than that of the base metal. Preheating is generally not required before welding, but in cold outdoor operations, in order to avoid condensation of water vapor, the joints or adjacent areas can be heated evenly. 

Note that the local temperature should not exceed 100 ℃, so as not to cause carbon agglomeration and cause intergranular corrosion. When welding, it is advisable to use small line energy, continuous and fast welding speed. Generally, no heat treatment is required after welding. If heat treatment is required, it must be heated to 1100-1150°C and then cooled rapidly.

Machinability：
The machining characteristics of 904L are similar to those of other austenitic stainless steels, and there is a tendency for tool sticking and work hardening during machining. Positive rake angle cemented carbide tools must be used, and vulcanized and chlorinated oil is used as cutting coolant. The equipment and process should be based on the premise of reducing work hardening. During the cutting process, slow cutting speed and feed amount should be avoided.

Production Process：
As a general-purpose corrosion-resistant material, 904L stainless steel sheet can be cold-rolled to obtain high-performance products, which can be used in many fields including food industry equipment, kitchen utensils and electronic industries. The use of each field is different, and the performance requirements of cold-rolled stainless steel 904L stainless steel are also different. 

Especially when the thickness of the stainless steel strip is small, it is extremely important to seek its comprehensive cold working performance. By analyzing the influence of rolling and annealing processes on its properties and microstructure, and studying the influence of production process parameters on its microstructure and properties, experimental data can be provided for on-site production optimization and performance improvement.

Stainless Steel 904L Application：

• Petroleum, petrochemical equipment, such as reactors in petrochemical equipment, etc.

• Storage and transportation equipment for sulfuric acid, such as heat exchangers, etc.

• The flue gas desulfurization device of power plant is mainly used in the following parts: the tower body, flue, baffle plate, internal parts, spray system, etc. of the absorption tower.

• Scrubbers and fans in organic acid treatment systems.

• Seawater treatment devices, seawater heat exchangers, paper industry equipment, sulfuric acid, nitric acid equipment, acid production, pharmaceutical industry and other chemical equipment, pressure vessels, food equipment.

• Pharmaceutical plants: centrifuges, reactors, etc.

• Plant food: equipment

• 904L is the matching steel grade for the strong corrosive medium of dilute sulfuric acid.