HASTELLOY
Hastelloy S Alloy UNS N06635 Bar
Nickel-molybdenum-chromium superalloy for applications combining thermal cycling and severe corrosion
Hastelloy S is engineered to provide superior thermal fatigue resistance combined with exceptional corrosion resistance in reducing and moderately oxidizing environments. The alloy's unique composition delivers outstanding performance in thermal cycling conditions while maintaining excellent resistance to halide-containing and sulfuric acid process streams.
Quick Specifications
- Density
- 8.75 g/cm³ (0.316 lb/in³)
- Melting Point
- 2450-2550°F (1343-1399°C)
- Yield Strength (0.2% offset)
- 80-100 ksi (552-690 MPa) at room temperature
- Tensile Strength
- 130-150 ksi (896-1034 MPa) at room temperature
- Elongation
- 25-35% in 2 inches
- Modulus of Elasticity
- 32.8 × 10⁶ psi (226 GPa) at 70°F
Standards & Certifications
Product Description
Hastelloy S represents an advanced nickel-molybdenum-chromium superalloy developed to address the challenging combination of thermal cycling and severe corrosion resistance requirements that defeat conventional materials. The alloy name derives from its application in severe environments combining these dual demands. While Hastelloy B3 excels in non-oxidizing acid resistance and C-22 dominates in oxidizing acid service, Hastelloy S occupies a critical niche for applications experiencing significant thermal cycling—such as furnace walls, reactor internals, and heat exchanger tubing—where thermal stress combined with corrosive attack creates service conditions beyond the capability of single-function alloys.
The metallurgical structure of Hastelloy S incorporates a carefully balanced composition of molybdenum, chromium, and iron that provides both thermal fatigue strength and corrosion resistance without sacrificing ductility. The alloy maintains excellent impact strength across a wide temperature range, a critical requirement for equipment experiencing rapid temperature fluctuations. Molybdenum additions provide strength in reducing acid environments while the chromium content provides passivity in mildly oxidizing conditions. Iron additions moderate the alloy's cost while maintaining performance, creating an economical solution to thermal cycling challenges that would otherwise require more exotic and expensive superalloys.
Hastelloy S exhibits outstanding resistance to thermal cycling and mechanical fatigue, maintaining structural integrity through hundreds of heating and cooling cycles that would cause premature failure in less sophisticated materials. The alloy's superior resistance to both pitting corrosion and stress-corrosion cracking in chloride-containing media ensures that corrosive attack does not accelerate under thermal cycling conditions. Critical pitting temperatures in synthetic seawater are markedly superior to conventional alloys, enabling the alloy to maintain integrity even in biofilm-covered heat exchanger tubing where oxygen depletion would normally initiate localized corrosion.
Applications for Hastelloy S concentrate on equipment where thermal cycling combines with moderate to severe corrosion to create conditions beyond the capability of conventional materials. The alloy's proven performance in furnace internals, thermal cycling reactors, and heat exchanger tubing in aggressive chemical processes demonstrates its ability to deliver extended service intervals in some of the industry's most demanding environments. The combination of strength, ductility, corrosion resistance, and thermal cycling capability makes Hastelloy S an invaluable tool for chemical process engineers seeking to maximize equipment reliability and operational efficiency.
Specifications
| Density | 8.75 g/cm³ (0.316 lb/in³) |
| Melting Point | 2450-2550°F (1343-1399°C) |
| Yield Strength (0.2% offset) | 80-100 ksi (552-690 MPa) at room temperature |
| Tensile Strength | 130-150 ksi (896-1034 MPa) at room temperature |
| Elongation | 25-35% in 2 inches |
| Modulus of Elasticity | 32.8 × 10⁶ psi (226 GPa) at 70°F |
| Thermal Conductivity | 7.0 BTU/hr·ft·°F at 212°F (12.1 W/m·K) |
| Coefficient of Thermal Expansion | 7.4 × 10⁻⁶ in/in·°F (13.3 × 10⁻⁶ m/m·°C) 68-212°F |
| Creep Rupture Strength (10,000 hrs @ 1200°F) | 15 ksi (103 MPa) |
| Hardness (Annealed) | ≤ 270 HB |
Chemical Composition
| Element | Content (%) |
|---|---|
| Nickel (Ni) | Balance |
| Molybdenum (Mo) | 16.0-18.0 |
| Chromium (Cr) | 15.0-17.0 |
| Iron (Fe) | 5.0-8.0 |
| Tungsten (W) | 2.0-4.0 |
| Cobalt (Co) | 0.0-2.0 |
| Aluminum (Al) | 0.0-0.5 |
| Titanium (Ti) | 0.0-0.5 |
| Manganese (Mn) | 1.0-2.0 |
| Carbon (C) | 0.03-0.08 |
| Silicon (Si) | 0.0-1.0 |
| Sulfur (S) | ≤ 0.02 |
| Phosphorus (P) | ≤ 0.02 |
Mechanical Properties
| Property | Value |
|---|---|
| Yield Strength @ 70°F | 80-100 ksi (552-690 MPa) |
| Tensile Strength @ 70°F | 130-150 ksi (896-1034 MPa) |
| Elongation (2 inch gauge) | 25-35% |
| Reduction of Area | 45-55% |
| Impact Strength (Charpy V-notch @ 32°F) | ≥ 90 ft·lbf (122 J) |
| Yield Strength @ 1000°F | 60 ksi (414 MPa) |
| Tensile Strength @ 1000°F | 105 ksi (724 MPa) |
| Creep Rupture Strength (10,000 hrs @ 1200°F) | 15 ksi (103 MPa) |
Key Features & Advantages
Applications
Thermal Cycling Chemical Reactors
Reactor internals, baffles, and heating/cooling coil supports in processes requiring frequent temperature changes. Hastelloy S maintains integrity through hundreds of thermal cycles while resisting corrosive attack from process streams, enabling reliable long-term operation in dynamic chemical synthesis environments.
Heat Exchanger Tubes and Tubing
Tubing in shell-and-tube heat exchangers exposed to thermal cycling and aggressive process fluids. The alloy's superior thermal cycling strength combined with pitting resistance enables use in applications where conventional materials fail prematurely due to the combined effects of thermal stress and corrosion.
Furnace Wall Tubes and Internals
Radiant section tubing, convection section tubing, and internal support structures in industrial furnaces experiencing rapid heating during firebox cycling and cooling during operational cycling. Hastelloy S resists both thermal cycling fatigue and corrosion from furnace atmosphere impurities.
Acid Regeneration Equipment with Thermal Cycles
Reactor vessels and associated equipment in acid recovery and regeneration processes where temperature fluctuations combine with corrosive acid exposure. The alloy delivers superior reliability compared to conventional materials that fail prematurely due to combined thermal and chemical attack.
Superheater and Reheater Tube Supports
Supports, baffles, and internal structures in power generation superheater tubing systems. Hastelloy S resists both thermal fatigue from steam temperature cycling and corrosion from steam-side contaminants and oxygen.
Chlor-Alkali and Chemical Processing Equipment
Anode supports, cathode structures, and cell internals in electrolytic processes where chloride-containing process streams combine with thermal cycling. The alloy's resistance to both chloride corrosion and thermal fatigue ensures reliable long-term performance in these challenging electrochemical environments.
Frequently Asked Questions
How does Hastelloy S differ from Hastelloy C-22 for corrosion resistance?
What thermal cycling capability does Hastelloy S provide?
Is Hastelloy S suitable for high-temperature oxidizing service like furnaces?
What are the machining recommendations for Hastelloy S bar stock?
What certifications and documentation are provided with Hastelloy S bar shipments?
Related Products
Interested in Hastelloy S Alloy UNS N06635 Bar?
Contact us for pricing, availability, and custom specifications. We provide mill test certificates and fast global shipping.
Get a Free Quote
