Stainless steel is a family of iron-based alloys containing a minimum of 10.5% chromium, which provides excellent corrosion resistance and durability. Depending on the alloying elements, stainless steels are categorized into five main types: Austenitic, Ferritic, Martensitic, Duplex, and Precipitation-Hardening (PH).
Stainless Steel of Specifications and Sizes
The corrosion resistance and mechanical properties of it depend on its chemical composition.
Chemical Composition of Stainless Steel
| Grade (Type) | Cr (%) | Ni (%) | C (%) | Mo (%) | Others |
|---|---|---|---|---|---|
| 304 (Austenitic) | 18-20 | 8-10.5 | ≤0.08 | – | Mn, Si |
| 316 (Austenitic) | 16-18 | 10-14 | ≤0.08 | 2-3 | Mn, Si |
| 430 (Ferritic) | 16-18 | ≤0.75 | ≤0.12 | – | Mn, Si |
| 410 (Martensitic) | 11.5-13.5 | ≤0.75 | ≤0.15 | – | Mn, Si |
| 2205 (Duplex) | 21-23 | 4.5-6.5 | ≤0.03 | 2.5-3.5 | N, Mn |
| 17-4PH (PH) | 15-17.5 | 3-5 | ≤0.07 | – | Cu, Nb |
Key Observations:
Chromium (Cr): Essential for corrosion resistance (forms a passive oxide layer).
Nickel (Ni): Stabilizes austenitic structure (improves ductility & toughness).
Molybdenum (Mo): Enhances resistance to pitting/crevice corrosion (e.g., 316 vs. 304).
Carbon (C): Affects hardness and weldability (lower C = better corrosion resistance).
Physical Properties of Stainless Steel
It exhibits unique physical characteristics based on its microstructure.
| Property | 304 (Austenitic) | 430 (Ferritic) | 410 (Martensitic) | 2205 (Duplex) |
|---|---|---|---|---|
| Density (g/cm³) | 8.0 | 7.7 | 7.7 | 7.8 |
| Melting Point (°C) | 1400-1450 | 1425-1510 | 1480-1530 | 1380-1450 |
| Thermal Conductivity (W/m·K) | 16.2 | 26.0 | 24.9 | 19.0 |
| Electrical Resistivity (μΩ·m) | 0.73 | 0.60 | 0.55 | 0.80 |
| Magnetic? | No (non-magnetic) | Yes | Yes | Partially |
Notes:
Austenitic (304/316): Non-magnetic, lower thermal conductivity.
Ferritic (430): Magnetic, better thermal/electrical conductivity.
Duplex (2205): Combines strength of austenitic & ferritic.
Mechanical Properties of Stainless Steel
Mechanical performance varies significantly by grade and heat treatment.
| Grade (Type) | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (Rockwell) |
|---|---|---|---|---|
| 304 (Austenitic) | 515-720 | 205-310 | 40-60 | B70-B90 |
| 316 (Austenitic) | 515-690 | 205-310 | 40-50 | B80-B95 |
| 430 (Ferritic) | 450-600 | 275-350 | 20-25 | B75-B85 |
| 410 (Martensitic) | 480-620 | 275-450 | 20-25 | B90-C25 |
| 2205 (Duplex) | 620-795 | 450-550 | 25-30 | B95-C30 |
| 17-4PH (Aged) | 1310-1450 | 1170-1310 | 10-15 | C35-C45 |
Key Takeaways:
Austenitic (304/316): High ductility, moderate strength (ideal for forming/welding).
Martensitic (410): Can be hardened via heat treatment (used for cutlery, tools).
Duplex (2205): Higher strength than austenitic, good corrosion resistance.
Precipitation-Hardening (17-4PH): Ultra-high strength after aging.
Comparison with Carbon Steel & Aluminum
| Property | Stainless Steel (304) | Carbon Steel (A36) | Aluminum (6061) |
|---|---|---|---|
| Corrosion Resistance | Excellent | Poor (rusts) | Good (oxidizes) |
| Strength (MPa) | 515-720 | 400-550 | 125-310 |
| Weight (g/cm³) | 8.0 | 7.85 | 2.7 |
| Cost | High | Low | Medium |
Stainless Steel
It also known as “Stainless Steel” in English, is a versatile metal alloy renowned for its corrosion resistance, mechanical strength, and aesthetic appeal. It is defined as a steel alloy with a chromium content of at least 10.5%, which forms a protective oxide layer on the surface, preventing rust and corrosion. Below is a detailed analysis of its properties, types, and applications. Durability: High strength-to-weight ratio; long lifespan with low maintenance. Hygienic: Non-porous surface resists bacterial growth (ideal for medical/food applications).
Advantages and Benefits of Stainless Steel
✔ Corrosion Resistance (Chromium oxide layer prevents rust).
✔ High Strength-to-Weight Ratio (Better than carbon steel).
✔ Hygienic & Easy to Clean (Widely used in food/medical industries).
✔ Temperature Resistance (Some grades withstand extreme heat/cryogenic temps).
✔ Aesthetic Appeal (Polished finish for architectural applications).
✔ Recyclability (100% recyclable, eco-friendly).
Application of Stainless Steel
- Construction: Facades, railings, roofing.
- Medical: Surgical tools, implants.
- Energy: Nuclear reactors, oil/gas pipelines.
- Automotive: Exhaust systems, decorative trim.
- Food Industry: Kitchen equipment, storage tanks.
| Grade | Type | Common Applications |
|---|---|---|
| 304 | Austenitic | Kitchen sinks, food processing, chemical tanks |
| 316 | Austenitic | Marine equipment, pharmaceutical, surgical tools |
| 430 | Ferritic | Automotive trim, appliances, decorative panels |
| 410 | Martensitic | Cutlery, turbine blades, fasteners |
| 2205 | Duplex | Oil & gas pipelines, desalination plants |
| 17-4PH | PH | Aerospace, nuclear, high-strength fittings |
In Conclusion
- Austenitic (304/316): Best for corrosion resistance & formability.
Ferritic (430): Cost-effective, magnetic, moderate corrosion resistance.
Martensitic (410): Heat-treatable for high hardness.
Duplex (2205): Combines strength + corrosion resistance.
PH (17-4PH): Ultra-high strength for demanding applications.
Stainless steel’s unique combination of corrosion resistance, mechanical strength, and versatility makes it indispensable in modern engineering. Selection depends on specific requirements, such as corrosion environment, temperature, and cost. Consultation with material engineers ensures optimal performance for each application.