What is 304 (AISI 304 Stainless Steel)?
AISI 304 Stainless Steel is a high-performance austenitic stainless steel renowned for excellent corrosion resistance, mechanical properties, and versatility. This comprehensive guide covers its chemical composition, mechanical properties, machining characteristics, and industrial applications per ASTM/GB standards.
Chemical Composition (ASTM A240/A276)
| Element | Content (%) | Specification |
|---|---|---|
| Chromium (Cr) | 18-20% | ASTM A240 |
| Nickel (Ni) | 8-12% | ASTM A240 |
| Carbon (C) | ≤0.08% | ASTM A240 |
| Manganese (Mn) | ≤2.0% | ASTM A240 |
| Silicon (Si) | ≤1.0% | ASTM A240 |
Mechanical Properties
| Property | Value | Standard |
|---|---|---|
| Tensile Strength | ≥515 MPa | ASTM A240 |
| Yield Strength (0.2% offset) | ≥205 MPa | ASTM A240 |
| Elongation | ≥40% (in 50mm) | ASTM A240 |
| Hardness | ≤201 HB / ≤92 HRB | ASTM E18 |
| Density | 8.0 g/cm³ | ASTM A484 |
Key Features
- Excellent corrosion resistance: Resistant to atmospheric corrosion, water, and many chemicals
- Good mechanical properties: High strength and ductility for various applications
- Easy to fabricate: Excellent formability and weldability
- Hygienic surface: Easy to clean, ideal for food and medical applications
- Heat resistant: Good oxidation resistance up to 800°C
- Cryogenic tough: Maintains toughness at low temperatures
Common Applications
- Kitchen equipment: Sinks, cookware, cutlery, food processing equipment
- Medical devices: Surgical instruments, implant trays, hospital equipment
- Architecture: Handrails, facades, elevator panels, decorative trim
- Chemical processing: Tanks, pipes, valves, heat exchangers
- Automotive: Exhaust systems, trim, fasteners, fuel tanks
- Marine: Boat fittings, marine hardware, desalination equipment
CNC Machining Guidelines
Tool Selection
- Tool material: Carbide (YG/YW class) or coated carbide for optimal performance
- Tool geometry: Positive rake angle (5-15°), relief angle (8-12°)
- Nose radius: 0.4-0.8mm for finishing, 0.8-1.2mm for roughing
Recommended Cutting Parameters
| Operation | Cutting Speed (m/min) | Feed Rate (mm/rev) | Depth of Cut (mm) |
|---|---|---|---|
| Rough Turning | 80-120 | 0.2-0.4 | 2-4 |
| Finish Turning | 120-180 | 0.05-0.15 | 0.2-0.5 |
| Milling | 100-150 | 0.1-0.3 | 1-3 |
| Drilling | 60-100 | 0.1-0.2 | N/A |
Coolant & Lubrication
- Coolant type: Emulsion or synthetic coolant with EP additives
- Coolant pressure: ≥5 MPa, directed at cutting zone
- Avoid dry cutting: Always use coolant to prevent work hardening
Surface Finish Options
- No. 1 (Hot rolled annealed): Rough matte finish
- 2B (Cold rolled): Smooth matte finish, most common
- No. 4 (Brushed): Directional satin finish
- No. 8 (Mirror): Highly reflective polished finish
- Bead blasted: Uniform matte texture
- PVD coating: Decorative colors (gold, black, blue, etc.)
Heat Treatment
- Solution annealing: 1010-1120°C, rapid cooling (water or air)
- Stress relieving: 200-300°C for cold worked parts
- Avoid sensitization: Do not hold in 425-870°C range for extended periods
