From food processing to chemical production, from architectural structures to medical devices, hardly any industry can completely eliminate the need for stainless steel. However, with a dazzling array of stainless steel grades available in the market, how does one select the most suitable option for specific needs? This article focuses on the most widely used 304 series stainless steel, analyzing its properties, applications, and differences between its sub-grades to help make informed material selection decisions.

304 stainless steel, also known as 18/8 stainless steel, is an austenitic chromium-nickel stainless steel. The "18/8" designation indicates its main composition of approximately 18% chromium and 8% nickel. The American Iron and Steel Institute (AISI) naming reflects its commercial availability. In addition to chromium and nickel, 304 stainless steel contains alloying elements such as manganese, silicon, nitrogen, carbon, phosphorus, and sulfur, whose synergistic effects provide excellent corrosion resistance and durability.

304 stainless steel is easily formable and can be processed into various complex structures, making it widely used in manufacturing, construction, and sanitary ware industries. Moreover, 304 stainless steel offers good weldability, maintaining excellent corrosion resistance after welding. Its relatively light weight makes it particularly favored in welding applications such as metal sheets, wire mesh products, and steam pipelines.

304 stainless steel is not monolithic; depending on different application requirements, several sub-grades have been developed, including 304L, 304H, and 304LN. These variants have slight differences in chemical composition, resulting in distinct performance characteristics.

The "L" stands for "low carbon." 304L stainless steel has a lower carbon content than standard 304 stainless steel, typically below 0.03%. While reduced carbon content slightly decreases structural strength, it significantly improves weldability. The lower carbon content minimizes the risk of carbide precipitation during welding, thereby enhancing the corrosion resistance of welded joints. Therefore, 304L stainless steel is often the better choice for applications requiring extensive welding and high corrosion resistance.

304L Stainless Steel Chemical Composition (%):

• Carbon: ≤0.03
• Chromium: 18.00-20.00
• Iron: Balance
• Manganese: ≤2.00
• Nickel: 8.00-12.00
• Nitrogen: ≤0.10
• Phosphorus: ≤0.045
• Silicon: ≤0.75
• Sulfur: ≤0.030

Applications of 304L Stainless Steel:

• Welding industry
• Heat exchangers
• Chemical containers
• Dyeing industry
• Mining welded screens

The "H" stands for "high carbon." 304H stainless steel has a higher carbon content than standard 304 stainless steel, typically between 0.04% and 0.10%. The increased carbon content enhances its high-temperature strength. In environments ranging from 550°C to 800°C, 304H stainless steel maintains good strength. Additionally, it offers excellent oxidation resistance, performing well even under intermittent use at 870°C or continuous use at 925°C.

304H Stainless Steel Chemical Composition (%):

• Chromium: 18.0-20.0
• Nickel: 8.0-10.5
• Carbon: 0.04-0.10
• Manganese: ≤2.00
• Phosphorus: ≤0.045
• Sulfur: ≤0.030
• Silicon: ≤0.75

Applications of 304H Stainless Steel:

• Boilers
• Heat exchangers
• Condensers
• Steam discharge equipment
• Power plants

304LN stainless steel is a variant of 304 stainless steel with added nitrogen. The inclusion of nitrogen increases its yield strength while maintaining good toughness. Furthermore, 304LN stainless steel exhibits excellent high-temperature performance, remaining stable even at 1000°C to 1100°C and demonstrating greater resistance to low-temperature martensitic transformation compared to 304L stainless steel.

304LN Stainless Steel Chemical Composition (%):

• Chromium: 18-20
• Nickel: 8-12
• Manganese: ≤2
• Silicon: ≤1
• Nitrogen: 0.1-0.16
• Phosphorus: ≤0.045
• Carbon: ≤0.03
• Sulfur: ≤0.03
• Iron: Balance

Applications of 304LN Stainless Steel:

• Nuclear industry
• Petroleum industry
• Chemical industry
• Food industry
• Manufacturing industry

Understanding the physical and chemical properties of 304 stainless steel helps in better selection and utilization.

Typical Physical Properties of 304 Stainless Steel:

Chemical Composition of 304 Stainless Steel (%):

• Corrosion Resistance: The most prominent feature of 304 stainless steel is its excellent corrosion resistance, capable of withstanding various corrosive media.
• Machinability: 304 stainless steel is easy to cut and form, meeting various complex manufacturing requirements.
• Thermal Processability: 304 stainless steel has good heat resistance and oxidation resistance, suitable for use at temperatures up to 870°C.
• Heat Treatment: 304 stainless steel cannot be hardened by heat treatment but can be annealed to improve machinability and yield strength.
• Weldability: 304 stainless steel has good welding properties and can be welded using various methods.
• Cold Workability: 304 stainless steel can be strengthened through cold working, but care must be taken to control the amount of processing to avoid cracks.

• Food and beverage industry
• Marine technology
• Seawater desalination plants
• Chemical industry
• Bridges
• Storage tanks
• Medical industry
• Civil engineering
• Power plants
• Shipbuilding industry
• Kitchen sinks and consumer goods
• Automotive and aerospace components
• Fastener and flange manufacturing

304 stainless steel, with its excellent corrosion resistance, good machinability, and wide range of applications, has become an indispensable material in the industrial sector. By understanding the properties of 304 stainless steel and its sub-grades, users can make better-informed decisions in material selection to meet various application needs.