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SUS 304 Stainless Steel: The Definitive Guide

10 May, 2024

Stainless steel is an indispensable material in modern society, renowned for its durability, corrosion resistance, and versatility. Among the various grades, SUS 304 stands out as one of the most widely used and versatile austenitic stainless steels. This comprehensive guide delves into the properties, composition, applications, and processing of SUS 304, providing valuable insights for industries ranging from food processing to construction.

Composition and Microstructure

SUS 304 stainless steel is an austenitic chromium-nickel alloy with a carefully balanced composition to achieve its desirable properties. It typically contains:

  • 18-20% Chromium (Cr)
  • 8-10.5% Nickel (Ni)
  • Less than 0.08% Carbon (C)
  • Trace amounts of other elements like Manganese, Silicon, Nitrogen, Phosphorus, and Sulfur

The Role of Chromium

The high chromium content is the key to SUS 304's excellent corrosion resistance. Chromium forms a passive oxide layer on the surface, protecting the underlying metal from corrosive environments . This self-healing layer is the reason why SUS 304 can withstand exposure to various chemicals, moisture, and atmospheric conditions without significant degradation.

The Importance of Nickel

Nickel plays a crucial role in stabilizing the austenitic microstructure of SUS 304 . This microstructure imparts superior ductility, toughness, and weldability to the alloy, making it suitable for a wide range of applications that require forming, bending, or joining processes.

Mechanical Properties

SUS 304 stainless steel exhibits impressive mechanical properties, contributing to its versatility and reliability:

  • Tensile Strength: The ultimate tensile strength ranges from 580 to 1180 MPa (84 to 170 ksi), while the yield strength varies from 230 to 860 MPa (34 to 120 ksi) .
  • Hardness: The Brinell hardness typically falls between 170 and 360 HB .
  • Elongation: SUS 304 can achieve an elongation at break of 8% to 43%, indicating its excellent ductility .
  • Fatigue Strength: The fatigue strength ranges from 210 to 440 MPa (30 to 63 ksi) .

These mechanical properties make SUS 304 suitable for applications that require a combination of strength, ductility, and toughness, such as pressure vessels, piping systems, and structural components .

Corrosion Resistance

One of the most significant advantages of SUS 304 stainless steel is its exceptional corrosion resistance, which is a direct result of its chromium content and the formation of the passive oxide layer. This layer protects the underlying metal from various corrosive environments, including:

  • Atmospheric corrosion
  • Mild chemical environments
  • Freshwater and seawater exposure (with limitations)

However, it is important to note that SUS 304 is susceptible to pitting and crevice corrosion in warm chloride environments like seawater or deicing salts . In these cases, the higher-alloyed SUS 316 stainless steel may be a better choice .

Weldability and Formability

Excellent Weldability

SUS 304 stainless steel exhibits excellent weldability, making it suitable for fabrication processes involving welding, such as pipe and pressure vessel manufacturing . It can be welded using various techniques, including shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), and gas metal arc welding (GMAW) .

Superior Formability

Additionally, SUS 304 has good formability, allowing it to be easily formed into various shapes through processes like rolling, bending, and drawing . This makes it a popular choice for applications requiring complex geometries, such as kitchen appliances, architectural components, and automotive parts .

Applications

Due to its versatile properties, SUS 304 stainless steel finds applications in numerous industries:

  • Food and Beverage: Food processing equipment, brewing tanks, kitchen appliances
  • Chemical and Pharmaceutical: Piping systems, reaction vessels, storage tanks
  • Construction and Architecture: Structural components, handrails, decorative elements
  • Transportation: Automotive trim, exhaust systems, marine components
  • Medical and Surgical: Surgical instruments, implants, medical equipment

The combination of corrosion resistance, strength, and formability makes SUS 304 a reliable and cost-effective solution for a wide range of applications across various industries.

Processing and Fabrication

Welding and Joining

SUS 304 stainless steel exhibits excellent weldability through conventional fusion techniques like SMAW, GTAW, and GMAW . For optimal corrosion resistance in welded components, post-weld annealing may be required . Alternatively, the low-carbon SUS 304L grade can be used to prevent sensitization during welding .

Forming and Machining

SUS 304 has good formability, making it suitable for various forming processes like rolling, bending, and deep drawing . It also has good machinability, although it is more challenging to machine than carbon steel due to work hardening . Dedicated tooling, rigid setups, and chip breakers are recommended for machining SUS 304 .

Heat Treatment

While SUS 304 cannot be hardened by heat treatment, solution annealing or stress-relieving can be performed to optimize its properties . Annealing is typically done by rapid cooling after heating to 1010-1120°C (1850-2050°F) .

Real-World Applications and Insights

At Xinguangyuan, a leading stainless steel manufacturer, SUS 304 finds extensive applications across various industries, leveraging the company's expertise and innovative solutions.

Food and Beverage Industry

One notable application is in the food and beverage sector, where clients rely on SUS 304 for its superior corrosion resistance and ease of cleaning. Xinguangyuan recently collaborated with a leading brewery to design and fabricate a state-of-the-art brewing system using SUS 304 stainless steel. The system's piping, tanks, and vessels were constructed from this durable material, ensuring a hygienic environment and preventing contamination during the brewing process .

Medical and Surgical Applications

In the medical field, SUS 304 is a popular choice for surgical instruments and implants due to its biocompatibility and resistance to corrosion from bodily fluids . Xinguangyuan has worked closely with medical device manufacturers to produce high-quality components that meet stringent safety and performance standards.

Architectural and Decorative Applications

Beyond these industries, SUS 304 stainless steel is widely used in architectural applications, such as handrails, decorative panels, and structural components . Its combination of strength, corrosion resistance, and aesthetic appeal make it an ideal material for both interior and exterior applications.

Xinguangyuan offers a wide range of SUS 304 stainless steel products, including hairline, etching, and mirror-finished sheets, tailored to meet the specific requirements of various industries . The company's commitment to sustainable manufacturing practices and innovative surface treatments further enhances the value and versatility of its SUS 304 offerings.

Conclusion

SUS 304 stainless steel is a versatile and widely used material that offers an excellent combination of corrosion resistance, mechanical properties, and formability. Its austenitic microstructure, balanced composition, and passive oxide layer contribute to its desirable characteristics, making it a popular choice across various industries.

At Xinguangyuan, a leading stainless steel manufacturer, they are committed to providing clients with high-quality SUS 304 stainless steel products and solutions. Their team of experts stays up-to-date with the latest industry developments and best practices, ensuring they deliver products that meet the highest standards of quality and performance.

Whether you require strength, ductility, or corrosion resistance, SUS 304 stainless steel is a reliable and cost-effective solution for a wide range of applications. Contact Xinguangyuan today to learn more about how they can assist you with your SUS 304 stainless steel needs.

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