1. Chemical Composition (Foundational Difference)
The variation in alloying elements directly shapes their thermal stability, strength, and corrosion resistance.
| Alloy | Key Elements (Typical Ranges, per ASTM/ASME Standards) |
|---|---|
| INCOLOY 800 | - Nickel (Ni): 30–35% (high content, critical for creep resistance and thermal stability)
- Chromium (Cr): 19–23% (for oxidation resistance)
- Iron (Fe): ~40–45% (base metal)
- Additives: Aluminum (Al: 0.15–0.60%), Titanium (Ti: 0.15–0.60%) (strengthen oxide film and prevent carbide precipitation)
- Carbon (C): ≤0.10% |
| SS 310 | - Nickel (Ni): 19–22% (lower than INCOLOY 800, supports austenite structure and high-temp ductility)
- Chromium (Cr): 24–26% (higher than INCOLOY 800, primary driver of oxidation resistance)
- Iron (Fe): ~50–55% (base metal)
- Manganese (Mn): ≤2.0% (aids formability)
- Carbon (C): ≤0.25% (310) / ≤0.08% (310S, low-carbon variant for reduced sensitization)
- No intentional Al/Ti additions |
INCOLOY 800 has higher nickel content and unique Al/Ti additives, while SS 310 features higher chromium content (for enhanced oxidation resistance) and no Al/Ti.
2. High-Temperature Performance (Strength vs. Oxidation Resistance)
Both alloys excel at high temperatures, but their strengths lie in different thermal properties-INCOLOY 800 prioritizes creep resistance, while SS 310 focuses on oxidation and scaling resistance.
| Aspect | INCOLOY 800 | SS 310 |
|---|---|---|
| Maximum Continuous Service Temp | Up to 1100°C (2012°F) (optimized for long-term load-bearing at high temps) | Up to 1200°C (2192°F) (higher than INCOLOY 800, but limited to low-load scenarios) |
| Creep Resistance | Excellent: Maintains structural integrity under long-term heat + stress (e.g., 100 MPa load at 800°C for 10,000 hours with minimal deformation). Al/Ti additions strengthen the matrix and prevent grain boundary sliding. | Moderate: Weaker than INCOLOY 800 under sustained loads at >800°C (e.g., 100 MPa load at 800°C may cause significant creep deformation within 1,000 hours). Lacks Al/Ti for matrix reinforcement. |
| Oxidation/Scaling Resistance | Very good: Forms a dense Cr₂O₃-Al₂O₃ oxide film that resists spallation (flaking) in air/steam up to 1100°C. | Excellent (superior to INCOLOY 800): High Cr content (24–26%) forms a thick, stable Cr₂O₃ film that withstands extreme heat (up to 1200°C) in oxidizing atmospheres (e.g., furnace atmospheres with high oxygen). Resists scaling better than INCOLOY 800 at >1100°C. |
| Thermal Fatigue Resistance | Strong: Withstands repeated heating/cooling cycles (e.g., boiler startup/shutdown) due to balanced thermal expansion and matrix strength. | Moderate: Prone to cracking under frequent thermal cycling (e.g., rapid heating from 200°C to 1000°C) due to higher thermal expansion coefficient and lower creep strength. |
INCOLOY 800 is a high-temperature load-bearing alloy (ideal for pressure vessels, tubes), while SS 310 is a high-temperature non-load-bearing alloy (ideal for static components like furnace liners).
3. Corrosion Resistance (Oxidative vs. General Corrosion)
Both resist high-temperature oxidation, but their performance in aqueous or chemical environments differs:
| Corrosion Environment | INCOLOY 800 | SS 310 |
|---|---|---|
| High-Temperature Oxidizing Gases | Very good (air, steam, CO₂ up to 1100°C) but outperformed by SS 310 at >1100°C. | Excellent (air, O₂, SO₂ up to 1200°C); best-in-class for oxidizing atmospheres with sulfur (e.g., industrial furnace exhausts). |
| Aqueous Corrosion (Room Temp) | Moderate: Resists dilute non-oxidizing acids (e.g., 10% H₃PO₄) and neutral water but prone to pitting in chloride-rich solutions (e.g., seawater). Poor resistance to strong oxidizing acids (e.g., concentrated HNO₃). | Moderate to good: Resists dilute acids (e.g., 5% H₂SO₄) and organic acids but also prone to chloride pitting (no molybdenum, unlike SS 316). Better than INCOLOY 800 in mild oxidizing acids (e.g., dilute HNO₃) due to higher Cr. |
| Stress Corrosion Cracking (SCC) | Resistant to SCC in water/steam but vulnerable in high-temperature H₂S or ammonia environments. | Prone to SCC in chloride-rich solutions (e.g., hot seawater) and caustic environments (e.g., concentrated NaOH). Lower SCC resistance than INCOLOY 800 in water/steam. |
| Sulfidation Resistance | Moderate: Susceptible to sulfidation (corrosion by sulfur) in reducing atmospheres (e.g., H₂S at >600°C). | Good: Higher Cr content improves resistance to sulfidation in mild reducing atmospheres, but still outperformed by nickel-based alloys like INCONEL 600. |
SS 310 outperforms INCOLOY 800 in extreme-temperature oxidizing/sulfur-rich atmospheres, while INCOLOY 800 offers better SCC resistance in water/steam and mild chemical environments.
4. Mechanical Properties (Room & High Temperatures)
INCOLOY 800's Al/Ti additions and higher Ni content deliver superior high-temperature strength, while SS 310 is more ductile at room temperature.
| Property (Room Temp, Solution-Annealed) | INCOLOY 800 | SS 310 |
|---|---|---|
| Ultimate Tensile Strength (UTS) | 550–650 MPa (80,000–94,000 psi) | 515–655 MPa (75,000–95,000 psi) |
| 0.2% Yield Strength (YS) | 200–280 MPa (29,000–40,600 psi) | 170–240 MPa (24,700–34,800 psi) |
| Ductility (% Elongation) | 30–40% | 40–50% (more ductile than INCOLOY 800) |
| Hardness (Brinell) | 140–180 HB | 130–170 HB (softer than INCOLOY 800) |
At High Temperature (800°C):
INCOLOY 800: UTS ≈ 250 MPa; 0.2% YS ≈ 100 MPa (sufficient for pressure-loaded components like boiler tubes).
SS 310: UTS ≈ 180 MPa; 0.2% YS ≈ 70 MPa (too weak for sustained loads; limited to static parts like furnace baffles).
5. Typical Applications (Reflecting Performance Priorities)
Their distinct strengths lead to specialized use cases:
| INCOLOY 800 Applications (High-Temp Load-Bearing) | SS 310 Applications (High-Temp Non-Load-Bearing/Oxidation Resistance) |
|---|---|
| - Power plant boiler tubes, steam superheater tubes (sustains pressure + heat) | - Industrial furnace liners, radiant heater shields (static, high-heat exposure) |
| - Nuclear power plant steam generators (resists creep + water/steam SCC) | - Kiln furniture (e.g., shelves for ceramic firing, withstands 1200°C) |
| - High-temperature heat exchangers (petrochemical, handles thermal cycling) | - Exhaust system components for incinerators (resists SO₂ oxidation) |
| - Pressure vessels for high-temperature chemical processes (e.g., acid distillation) | - Heat treating baskets/trays (holds parts in furnaces, no pressure load) |
6. Cost & Availability
INCOLOY 800: More expensive (higher Ni content + Al/Ti additives); classified as a "superalloy," so it is less widely available and often requires custom ordering for large quantities.
SS 310: Lower cost (lower Ni than INCOLOY 800, no rare additives); widely available as standard stainless steel (sheets, tubes, bars) from most metal suppliers.
