304 Stainless Steel: Composition, Properties, Processing, and Application Guidelines for Derivative Grades

304 stainless steel is one of the most commonly used stainless steels in the 300 series austenitic alloys. Its main components are 18%-20% chromium and 8%-10.5% nickel, offering excellent corrosion resistance, strength, and formability. In the annealed state, it is non-magnetic and maintains toughness even in low-temperature environments, making it suitable for a wide range of applications in industries such as automotive, food processing, medical, chemical, and construction.

1. Equivalent Grades of 304

2. Chemical Composition of 304 Stainless Steel (ASTM A959)

The synergistic effect between chromium and nickel determines the corrosion resistance and microstructural stability of 304 stainless steel. Chromium forms a dense passive film (Cr2O3) on the surface, which can self-repair even if damaged; nickel maintains the material's non-magnetic properties and good formability.

3. Mechanical Properties

304 offers a combination of high tensile strength, excellent ductility, and good toughness, making it one of the most versatile materials for structural components and precision parts. Its specific mechanical properties depend on the metallurgical state—annealed or cold worked.

In the annealed state, 304 stainless steel provides the best balance of strength and ductility, making it highly suitable for forming and welding. After cold working (such as rolling, drawing, or forming), its yield and tensile strengths can nearly double, making it ideal for structural components, fasteners, springs, and other parts requiring high strength and corrosion resistance. Additionally, 304 stainless steel maintains excellent toughness even in extremely low-temperature environments (-196°C), which is a key reason for its widespread use in cryogenic storage tanks and cryogenic pipelines (such as liquid nitrogen and liquid oxygen systems).

4. Physical Properties

The physical characteristics of 304 stainless steel have significant impacts on its thermal stability, thermal expansion, and electrical properties.

5. Corrosion Resistance

The corrosion behavior of 304 stainless steel varies depending on the surrounding environment:

6. Machining Performance and Manufacturing Characteristics

Forming Performance

304 austenitic stainless steel has good plasticity, suitable for cold/hot forming, deep drawing, bending, and stamping. It can achieve small bending radii (r/t ≈ 1). Cold working hardens the material, and annealing (900-950°C) should be performed when necessary. Engineering Tip: For deep drawing/multi-stage forming, 304L is preferred to reduce cracking risks.

Welding Performance

Welding methods include TIG, MIG, SMAW, and spot welding. The weld strength is comparable to the base material. High carbon content or slow cooling can lead to intergranular corrosion. Using 304L or post-weld solution annealing can prevent this. Pay attention to shielding gas purity, segmented welding, and cooling support. Common welding wires: ER308/ER308L; for dissimilar steels, ER309 can be used.

Machining Performance

Machining hardening is significant, with poor thermal conductivity and long, entangling chips. Optimization: Use cemented carbide/coated tools, medium-to-high feed rates, high-pressure cooling, and chip control. Machining efficiency can reach 70-80% of 303 steel.

Hot Working and Heat Treatment

Hot Forging/Hot Rolling: 1150-950°C, uniform heating followed by rapid cooling.Solution Annealing: 1040-1120°C, water quenching; Stress Relief Annealing: 900-950°C, air cooling.Avoid prolonged heating at 425-870°C to prevent sensitization; avoid excessive heating that causes surface oxidation.

Surface Treatment and Polishing

Surface types: 2B (smooth industrial), BA (mirror), No.4 (satin), 8K (highly reflective).Avoid iron contamination; after polishing, perform passivation or electrolytic polishing. For food/medical equipment, surface roughness (Ra) should be ≤0.8μm.

7. Common Grade Derivatives

304 – General BenchmarkCore Features: Best balance of strength, formability, and corrosion resistance.Key Composition: C ≤ 0.08%Main Advantages: All-around performer, most widely applied.Limitations: Risk of sensitization (intergranular corrosion) during welding or use at high temperatures (425-815°C).Typical Applications: Cookware, household appliances, building decorations, pipes, food equipment (non-welded or lightly welded).304L – Low-Carbon TypeCore Features: Extremely low carbon content, designed for welding and sensitization resistance.Key Composition: C ≤ 0.03%Main Advantages: Excellent weldability, strong resistance to intergranular corrosion after welding or in high-temperature sensitization ranges.Limitations: Slightly lower room-temperature strength than 304.Typical Applications: Large welded structures, chemical containers, pipes, high-temperature components in corrosive environments.304H – High-Temperature TypeCore Features: Higher carbon content to enhance high-temperature strength.Key Composition: C = 0.04-0.10%Main Advantages: Higher creep strength and endurance strength at high temperatures (>500°C).Important Warning: Extremely sensitive to sensitization; must not be used for components that will serve in corrosive environments after welding.Typical Applications: Boiler tubes, superheaters, steam pipes, and other high-temperature pressure equipment.304N – Nitrogen-Strengthened TypeCore Features: Adds nitrogen to increase room-temperature strength.Key Composition: N = 0.10-0.16%Main Advantages: Significantly higher room-temperature strength than 304 through nitrogen solid solution strengthening, while maintaining good ductility and corrosion resistance.Purpose: Reduces equipment weight or withstands higher loads while retaining corrosion resistance.Typical Applications: Structural components requiring higher strength, bridges, vehicle parts.304LN – Low-Carbon Nitrogen-Strengthened TypeCore Features: Combines the advantages of 304L and 304N.Key Composition: C ≤ 0.03%, N = 0.10-0.16%Main Advantages: Combines the sensitization resistance of 304L (low carbon) and the high strength of 304N (nitrogen addition). It is one of the strongest options for welded components.Typical Applications: Demanding scenarios requiring both high strength and excellent weldability and corrosion resistance, such as advanced chemical equipment, offshore platform structures.304LHN – Ultra-Low Carbon High-Nitrogen TypeInterpretation: A further optimization of 304LN, can be considered an "enhanced version of 304LN."L: Ultra-low carbon (C ≤ 0.03%)H: High nitrogen (N > 0.15%, specific range can reach about 0.20%, depending on standards)N: Indicates nitrogen contentCore Features: Provides higher strength than 304LN while ensuring sensitization resistance through higher nitrogen content. Its strength can easily exceed standard 304.Main Advantages: Extremely high strength + excellent sensitization resistance.Typical Applications: Fields with extremely demanding requirements for both strength and corrosion resistance, such as nuclear power plant critical components, deep-sea equipment, high-strength and weldable military or aerospace components.

Conclusion304 stainless steel is a reliable mainstay material in engineering and manufacturing. Its balance of corrosion resistance, strength, hygiene, and formability makes it the default choice for countless applications, from everyday household items to critical industrial components. Understanding its characteristics, limitations, and correct processing techniques is essential for successful use of 304 stainless steel in any project. For applications exposed to high-chloride environments or requiring higher strength, consider its variants (such as 304L) or other grades (such as 316 or 316L).