SUS304 Austenitic knowledge

SUS304 is a widely used austenitic stainless steel, renowned for its excellent general corrosion resistance, formability and cost-effectiveness. It contains balanced chromium (18–20%) and nickel (8–10.5%) content, forming a dense chromium oxide layer on the surface to resist atmospheric, mild acid and alkaline corrosion, making it a staple in general industrial and consumer applications.

Chemical Composition (Key, % JIS G4305): C≤0.08; Cr18.0–20.0; Ni8.0–10.5; Mn≤2.0; Si≤1.0

Mechanical Properties (Annealed): Tensile Strength≥515MPa; Yield Strength≥205MPa; Elongation≥40%; Hardness≤201HB

Performance Advantages: Superior general corrosion resistance; excellent formability for bending and stamping; good weldability; cost-effective for mass production.

Applications: Kitchen appliances, architectural trim, food processing equipment, chemical storage tanks (non-aggressive media).

Equivalent Grades: ASTM 304, EN 1.4301, DIN X5CrNi18-10

Comparison with SUS304L: SUS304 has higher carbon content (≤0.08% vs. ≤0.03% of 304L), offering better high-temperature strength, but is prone to intergranular corrosion after welding; 304L avoids this issue without post-weld heat treatment.

FAQs

Why is SUS304 the most widely used stainless steel grade? SUS304 strikes an ideal balance between corrosion resistance, mechanical properties and cost, which is the core reason for its popularity. Its 18–20% chromium content forms a stable protective oxide layer, resisting rust and mild chemical attacks in most daily and industrial environments. Unlike higher-grade alloys such as 316, SUS304 does not contain expensive molybdenum, so it has a lower production cost, suitable for large-scale applications. Its excellent formability allows manufacturers to process it into various shapes, from kitchen sinks to architectural panels, meeting diverse application needs. In addition, its good weldability ensures the structural integrity of welded components, further expanding its application scope in construction and manufacturing industries.

 

What is the maximum service temperature of SUS304? The continuous maximum service temperature of SUS304 is about 870°C, but its performance will vary depending on the specific environment and stress conditions. At temperatures below 650°C, SUS304 retains most of its mechanical strength and corrosion resistance, making it suitable for heat exchangers and industrial oven parts. When the temperature exceeds 650°C, its yield strength begins to decrease significantly, but it can still be used for non-load-bearing components such as furnace liners. However, when exposed to temperatures between 425°C and 815°C for a long time, SUS304 may experience sensitization, leading to intergranular corrosion, especially after welding. Therefore, for high-temperature welded applications, it is more appropriate to choose stabilized grades such as SUS321 or low-carbon grade SUS304L.

Can SUS304 be used in marine environments? SUS304 has limited applicability in marine environments and is not recommended for long-term use in saltwater or coastal areas with high humidity. The high chloride content in seawater will break down the chromium oxide protective layer of SUS304, leading to pitting and crevice corrosion, which will reduce the service life of components. Although it can resist slight salt spray corrosion in short-term or low-chloride scenarios, for long-term marine applications such as ship parts or offshore platforms, molybdenum-containing grades such as SUS316 are better choices, because molybdenum can enhance the resistance to chloride-induced corrosion. If SUS304 must be used in marine-related applications, regular maintenance and anti-corrosion coating treatment are required to extend its service life.

 

How to properly weld SUS304 to avoid corrosion issues? Welding SUS304 requires strict control of heat input and selection of appropriate filler materials to minimize the risk of intergranular corrosion. First, choose SUS308 or SUS309 filler wire, which has a higher nickel content than SUS304, helping to stabilize the austenitic structure of the weld and reduce the tendency of hot cracking. During the welding process, use low heat input parameters, shorten the welding time, and reduce the size of the heat-affected zone (HAZ), because excessive heat will promote the formation of chromium carbides in the HAZ, leading to sensitization. After welding, it is recommended to perform post-weld heat treatment (annealing at 1010–1120°C and water quenching) to dissolve chromium carbides and restore the corrosion resistance of the weld area. In addition, cleaning the weld surface after welding to remove oxide scale and impurities can also help improve corrosion resistance.

 

What is the difference between SUS304 and SUS316 in terms of corrosion resistance? The core difference in corrosion resistance between SUS304 and SUS316 lies in the presence of molybdenum in SUS316, which significantly enhances its resistance to chloride-induced pitting and crevice corrosion. SUS304 can only resist general atmospheric corrosion and mild chemical corrosion, but is prone to corrosion in chloride-rich environments such as seawater and brine. SUS316 contains 2–3% molybdenum, which can stabilize the passive film on the steel surface, preventing chloride ions from penetrating and damaging the protective layer. In addition, SUS316 has a higher nickel content (10–14%) than SUS304 (8–10.5%), which improves its high-temperature stability and toughness. Therefore, SUS316 is more suitable for harsh environments such as marine engineering, chemical processing and medical equipment, while SUS304 is sufficient for general-purpose applications with lower cost.