ISO X10CrNi25-21 Stainless Steel: High-Performance Austenitic Alloy for Extreme Temperature and Corrosion Resistance
ISO X10CrNi25-21 (UNS S31050) is a high-alloy austenitic stainless steel designed for exceptional performance in elevated temperature and highly corrosive environments. With a nominal composition of 25% chromium and 21% nickel, this grade offers superior oxidation resistance up to 1100°C, excellent creep strength, and resistance to sulfur-containing atmospheres. It is widely specified for furnace components, petrochemical processing equipment, and high-temperature heat exchangers where conventional 300-series stainless steels would fail. This technical guide examines its chemical properties, mechanical characteristics, processing requirements, and industrial applications.
1. Chemical Composition (EN 10088-3 Standard)
| Element | Content Range | Function |
|---|---|---|
| Carbon (C) | 0.08-0.12% | Enhances high-temperature strength; controlled to prevent carbide precipitation during welding |
| Chromium (Cr) | 24.00-26.00% | Forms dense Cr₂O₃ oxide layer; provides exceptional oxidation and sulfidation resistance |
| Nickel (Ni) | 19.00-22.00% | Stabilizes austenitic microstructure; improves ductility and thermal shock resistance |
| Manganese (Mn) | ≤ 2.00% | Enhances hot workability; acts as deoxidizer during melting |
| Silicon (Si) | ≤ 1.50% | Improves scale resistance at temperatures above 900°C; enhances fluidity in casting |
| Phosphorus (P) | ≤ 0.040% | Minimized to prevent embrittlement and reduce susceptibility to intergranular corrosion |
| Sulfur (S) | ≤ 0.015% | Ultra-low content prevents hot cracking and improves weldability |
| Iron (Fe) | Balance | Base metal providing structural integrity |
2. Mechanical Properties at Elevated Temperatures
| Property | Room Temperature | 500°C | 800°C | 1000°C |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 540 | ≥ 410 | ≥ 180 | ≥ 80 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 | ≥ 100 | ≥ 40 |
| Elongation (%) | ≥ 40 | ≥ 30 | ≥ 25 | ≥ 20 |
| Creep Rupture Strength (100,000h, MPa) | – | 120 | 60 | 20 |
3. Manufacturing and Processing Characteristics
- Melting Practice: Triple-melted using VIM (Vacuum Induction Melting) + ESR (Electroslag Remelting) + VAR (Vacuum Arc Remelting) to ensure ultra-low inclusions and superior homogeneity for critical applications.
- Hot Working: Forging/rolling temperature range of 1150-1250°C; requires uniform heating to prevent delta-ferrite formation. Rapid cooling after hot working to maintain corrosion resistance.
- Cold Working: Limited cold formability due to high work hardening rate; intermediate annealing at 1050-1150°C required for complex shapes. Springback must be accounted for in design.
- Heat Treatment: Solution annealing at 1050-1150°C followed by water quenching or rapid air cooling. Stress relief annealing at 800-900°C for welded components to prevent stress corrosion cracking.
- Machining: Requires rigid machine setups and sharp tools (cobalt-grade HSS or carbide). Use sulfurized or chlorinated cutting oils; maintain low speeds (50-60% of carbon steel) and high feeds to prevent work hardening.
- Welding: Suitable for all standard methods (TIG, MIG, SMAW). Use AWS ER310 or ER353 filler metals. Preheat not required; maintain interpass temperature below 150°C. Post-weld annealing recommended for maximum corrosion resistance.
4. Key Industrial Applications
Petrochemical Processing
Ethylene pyrolysis tubes, reformer furnaces, and sulfur recovery units where resistance to carburization and metal dusting is critical. Performs reliably in hydrogen-rich environments up to 1100°C.
Furnace Components
Radiant tubes, muffles, retorts, and heat treatment fixtures in continuous annealing lines and bright annealing furnaces. Maintains dimensional stability during thermal cycling.
Power Generation
Boiler superheater tubes, gas turbine components, and flue gas desulfurization systems. Resists vanadium attack in heavy fuel oil combustion environments.
Aerospace & Defense
Jet engine exhaust systems, afterburner components, and missile structural parts requiring oxidation resistance at Mach 2+ velocities. NASA-specified for spacecraft thrust chambers.
Glass Manufacturing
Forehearths, spouts, and stirrers in float glass production. Resists corrosion from molten glass and alkali vapors at 1400°C. Used in fiberglass bushings for continuous filament production.
Waste Incineration
Grate systems, secondary combustion chamber linings, and flue gas scrubbers. Withstands chlorides, sulfates, and mixed acid condensates in municipal waste-to-energy plants.
5. Comparison with Related High-Temperature Alloys
| Alloy | Cr-Ni Content | Max Service Temp (°C) | Key Advantages | Limitations |
|---|---|---|---|---|
| X10CrNi25-21 | 25Cr-21Ni | 1100 | Best balance of oxidation/sulfidation resistance and creep strength; cost-effective for continuous service | Limited resistance to nitriding atmospheres; higher thermal expansion than ferritic alloys |
| 310S (X6CrNi25-20) | 25Cr-20Ni | 1050 | Lower carbon version for improved weldability; widely available | Slightly lower creep rupture strength than X10CrNi25-21 |
| 330 (N08330) | 35Cr-35Ni | 1150 | Superior carburization resistance; excellent thermal shock resistance | Higher cost; more difficult to machine due to work hardening |
| 601 (N06601) | 23Cr-60Ni | 1200 | Highest temperature capability; exceptional resistance to oxidizing/sulfidizing environments | Premium pricing; limited availability in certain product forms |
| HR120 (N08120) | 37Cr-33Ni | 1200 | Outstanding resistance to metal dusting and carburization; high rupture strength | Very high alloy cost; specialized welding procedures required |
6. Selection and Application Guidelines
- Temperature Limitations: While capable of 1100°C intermittent service, continuous operation above 1050°C may require derating. Consult ASME Section II Part D for allowable stress values at specific temperatures.
- Corrosive Environments: Not recommended for reducing acids (HCl, H₂SO₄) or halogen gases. For chloride-containing atmospheres above 600°C, consider silicon-modified grades like 330 or 601.
- Thermal Expansion: Coefficient of thermal expansion (17.2 µm/m·°C at 20-100°C) is ~50% higher than carbon steel. Design joints and supports to accommodate expansion/contraction cycles.
- Surface Preparation: For maximum oxidation resistance, remove all contaminants and perform passivation with 20-40% nitric acid at 60-70°C for 2 hours. Electropolishing can further enhance surface corrosion resistance.
- Quality Certification: Verify material test reports (MTRs) confirm compliance with EN 10095, ASTM A240, or AISI 310S standards. For aerospace applications, request NADCAP-approved processing.
- Alternative Forms: Available as sheet (0.5-6mm), plate (6-50mm), bar, wire, and seamless pipe. For complex fabrications, consider centrifugal castings which offer superior creep resistance in tubular components.
7. Request a Technical Quote for X10CrNi25-21 Stainless Steel
Require precision-engineered X10CrNi25-21 stainless steel for your high-temperature application? Our metallurgical experts provide comprehensive technical support including material selection, fabrication advice, and competitive pricing for:
- Custom-cut sheets and plates with certified mill test reports
- Seamless pipes and tubes for furnace applications
- Forged bars and machined components to your specifications
- Welding consumables and fabrication services