An in-depth overview of 304 stainless steel—its standards, composition, properties, applications, and precautions—tailored for industry professionals and buyers.
Table of Contents
- Global Standards for 304 Stainless Steel
- Chemical Composition & Key Element Functions
- Mechanical Properties
- Modified Variants of 304
- Comparison with Other Stainless Steel Grades
- Typical Applications
- Common Forms & Surface Finishes
- Critical Usage Precautions
- About Us
1. Global Standards for 304 Stainless Steel
304 stainless steel is designated differently across international standards. Below is the direct correspondence for easy reference:
| Country/Region | Standard System | Grade/Designation |
|---|---|---|
| United States | AISI (American Iron and Steel Institute) / UNS | 304 (UNS S30400) |
| China | GB/T 3280 (National Standard for Cold-Rolled Stainless Steel Sheets/Strips) | 06Cr18Ni9 |
| Japan | JIS (Japanese Industrial Standards) | SUS304 |
| United Kingdom | BS EN (British Adopted European Standard) | 304S15 |
| European Union | EN 10088 (European Standard for Stainless Steels) | 1.4301 |
| South Korea | KS (Korean Industrial Standards) | STS304 |
| India | IS 6911 (Indian Standard for Stainless Steels) | 07Cr18Ni9 |
2. Chemical Composition & Key Element Functions
304 stainless steel (abbreviated as SS 304) is an austenitic alloy defined by its strict chemical composition.
2.1 Chemical Composition (Mass Fraction, %)
| Element | Fe (Iron) | Cr (Chromium) | Ni (Nickel) | Mn (Manganese) | Si (Silicon) | C (Carbon) | P (Phosphorus) | S (Sulfur) |
|---|---|---|---|---|---|---|---|---|
| Content Range | Balance | 18–20 | 8–10 | ≤2.0 | ≤1.0 | ≤0.08 | ≤0.045 | ≤0.03 |
2.2 Key Element Roles
- Chromium (Cr): The core of corrosion resistance. It reacts with oxygen to form a dense Cr₂O₃ passive film that blocks further oxidation. A minimum of 12% Cr is required for “stainless” properties.
- Nickel (Ni): Stabilizes the austenitic structure (non-magnetic at room temperature), maintains high ductility, and enhances resistance to acids/alkalis.
- Manganese (Mn): Acts as a deoxidizer and desulfurizer during steelmaking. Excessive Mn (>2.0%) weakens corrosion resistance and weldability.
- Carbon (C): Boosts tensile strength but reduces ductility. High carbon content also increases the risk of corrosion (avoiding >0.08% is critical).
- Phosphorus (P) & Sulfur (S): Harmful impurities. They degrade weldability, plasticity, and cold-forming performance—hence strict upper limits.
3. Mechanical Properties
The following are typical mechanical properties for 304 stainless steel coils (the most widely used form):
| Test Item | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Vickers Hardness (HV) |
|---|---|---|---|---|
| Industry Standard | ≥700 | ≥280 | ≥53 | ≤170 |
Note: Properties may vary slightly by processing (e.g., annealing, cold rolling) to meet specific application needs.
4. Modified Variants of 304
To address specialized requirements (e.g., welding, deep drawing), 304 has been optimized into several variants:
| Variant | Core Modification | Key Advantage | Suitable Scenarios |
|---|---|---|---|
| 304L | Low carbon (C ≤ 0.03%) | Prevents carbide precipitation during welding (avoids intergranular corrosion) | Welded components (e.g., industrial pipelines, tanks) |
| 304N | Added nitrogen (0.10–0.16%) | Improves cold-forming performance and strength without reducing ductility | Cold-formed parts (e.g., automotive structural components) |
| 304D | Nickel-reduced (2.8% Ni) | Cost-effective; maintains tensile strength | Non-corrosive industrial applications (not for kitchenware) |
| 304J1 | Added copper + reduced nickel | Higher tensile strength than standard 304 | Low-corrosion industrial parts (e.g., brackets) |
| 304DQ | Optimized annealing process (no composition change) | Enhanced deep-drawing performance | Kitchenware (e.g., pots, sinks) and complex-shaped stamped parts |
5. Comparison with Other Stainless Steel Grades
304 is often compared to other common grades—here’s how it stacks up:
5.1 304 vs. 316
| Aspect | 304 | 316 |
|---|---|---|
| Key Difference | No molybdenum; 8–10% Ni | Contains 2–3% molybdenum; 10–14% Ni |
| Corrosion Resistance | Good for general environments (e.g., dry air, fresh water) | Excellent for chloride-rich environments (seawater, sweat, salt) |
| Best For | Kitchenware, daily hardware | Marine parts, medical equipment, chemical tanks |
| Cost | Economical | ~1.5x higher than 304 |
5.2 304 vs. 430
| Aspect | 304 | 430 |
|---|---|---|
| Structure | Austenitic (non-magnetic) | Ferritic (magnetic) |
| Corrosion Resistance | High (Cr+Ni alloy) | Low (Cr-only; no Ni) |
| Ductility | Excellent (good for deep drawing) | Poor (brittle at low temperatures) |
| Thermal Conductivity | Lower | Higher (better for heat transfer) |
| Usage | Food-grade, high-corrosion needs | Decorative parts (e.g., appliance trims) |
5.3 304 vs. 201 (Non-Food-Grade)
| Aspect | 304 | 201 |
|---|---|---|
| Food Safety | Food-grade (safe for contact with food) | Non-food-grade (high Mn; risks leaching in acidic environments) |
| Corrosion Resistance | High | Low (prone to rust in humid areas) |
| Ductility | Good | Brittle (high carbon content) |
| Application | Kitchenware, food equipment | Low-cost decorative parts (e.g., door handles) |
6. Typical Applications
304’s balanced performance makes it the most versatile stainless steel grade, used across industries:
- Food Industry: Food processing equipment, food-grade kitchenware (pots, pans, utensils), and storage containers.
- Automotive: Windshield wipers, mufflers, fuel tanks, and decorative trim.
- Medical: Non-critical medical devices (e.g., drug storage cabinets, instrument trays).
- Construction: Indoor roofing, wall cladding, handrails, and elevator panels (ideal for dry environments).
- Industrial: Chemical tanks (non-aggressive fluids), water treatment components, and industrial fasteners.
7. Common Forms & Surface Finishes
7.1 Main Forms
- Coils: The primary form (wide-width rolls). Processed into sheets, plates, or strips for downstream manufacturing.
- Bars/Rods: Used for machining parts (e.g., bolts, screws).
- Tubes/Pipes: For fluid transport (e.g., water pipes, industrial pipelines).
- Custom Castings: Tailored to complex shapes (e.g., valve bodies, pump components).
7.2 Surface Finishes
Finishes are chosen for aesthetics, corrosion resistance, or functionality:
| Finish Grade | Roughness (Ra, μm) | Description | Common Name |
|---|---|---|---|
| 11 | 0.1–0.2 | High-gloss mirror; no visible defects | 8K Mirror Finish |
| 10 | 0.2–0.3 | Semi-mirror; faint hairline visible | 6K Mirror Finish |
| 9 | 0.4 | Near-matte; similar to bright annealed (BA) finish | 4K Mirror Finish |
| Hairline | – | Uniform linear texture; non-reflective | Satin Finish |
| Color Plating | – | Coated with gold, black, or beige (via PVD/electroplating) | Decorative Finish |
8. Critical Usage Precautions
- Avoid Chloride Exposure: Chloride ions (found in salt, sweat, seawater, or soy sauce) rapidly corrode 304. For long-term contact with chlorides, use 316 instead.
- Kitchenware Selection: For deep-drawn items (e.g., sinks), choose 304DQ (not standard 304) to prevent cracking during forming.
- Magnetism Misconception: 304 is non-magnetic in its original state, but heavy deformation (e.g., stamping) may induce weak magnetism. Do not use “magnet testing” as a reliable way to identify 304.
- Post-Processing Cracking: Austenitic stainless steel (like 304) may crack 5 minutes to 10 days after heavy stretching (due to internal stress). Contact us for stress-relief solutions.
9. About Us
We are a professional supplier of 304 stainless steel (coils, sheets, tubes, and custom parts) with strict quality control aligned with global standards. For inquiries about 430, 410, 201, or other stainless steel grades, contact our team for personalized quotes and technical support.
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