If you work with aggressive chemicals like nitric acid or mixed acidic solutions—where other alloys fail—UNS N06455 Hastelloy C4 is your reliable solution. This nickel-chromium-molybdenum alloy stands out for its exceptional resistance to intergranular corrosion and harsh chemical environments, making it a top pick for demanding industries. This guide breaks down its key properties, real-world uses, manufacturing methods, and how it compares to other materials—so you can make informed decisions for your project.
1. Material Properties of UNS N06455 Hastelloy C4
Hastelloy C4’s performance stems from its carefully balanced composition and unique traits that combat corrosion and maintain strength. Let’s explore each property clearly.
1.1 Chemical Composition
Every element works together to enhance corrosion resistance and stability—with ultra-low carbon to prevent intergranular damage. Below is its typical composition (by weight):
| Element | Content Range (%) | Key Role |
|---|---|---|
| Nickel (Ni) | 65–70 | Base metal—provides ductility and resists stress cracking |
| Chromium (Cr) | 14–18 | Enhances oxidation resistance and fights pitting in acidic liquids |
| Molybdenum (Mo) | 14–17 | Blocks corrosion in strong acids (e.g., nitric, sulfuric) |
| Tungsten (W) | Max 0.5 | Boosts resistance to localized corrosion (pitting, crevice) |
| Iron (Fe) | Max 3.0 | Adds structural strength without reducing corrosion resistance |
| Carbon (C) | Max 0.015 | Ultra-low to prevent carbide formation (avoids intergranular corrosion) |
| Manganese (Mn) | Max 1.0 | Aids in manufacturing (e.g., welding and casting) |
| Silicon (Si) | Max 0.08 | Reduces oxidation at high temperatures |
| Sulfur (S) | Max 0.01 | Kept low to prevent brittleness in harsh environments |
| Copper (Cu) | Max 0.5 | Improves resistance to certain acids (e.g., sulfuric acid) |
| Cobalt (Co) | Max 2.0 | Enhances high-temperature stability (ideal for aerospace parts) |
1.2 Physical Properties
These traits make Hastelloy C4 easy to design with for tough industrial tasks:
- Density: 8.6 g/cm³ (heavier than stainless steel, lighter than Hastelloy B2)
- Melting Point: 1320–1370°C (2408–2498°F) – handles high-heat processes like chemical reactions
- Thermal Conductivity: 12.1 W/(m·K) at 20°C (68°F); 19.8 W/(m·K) at 600°C – efficient heat transfer
- Thermal Expansion Coefficient: 12.7 μm/(m·K) (20–100°C); 16.1 μm/(m·K) (20–600°C) – minimal warping when heated or cooled
- Electrical Resistivity: 138 Ω·mm²/m at 20°C – suitable for electrical components in corrosive, high-heat areas
- Magnetic Properties: Non-magnetic – great for medical, electronic, and aerospace equipment where magnetism is a problem
1.3 Mechanical Properties
Hastelloy C4 balances strength and flexibility, even at high temperatures. All values below are for the annealed (heat-treated) version:
| Property | Value (Room Temperature) | Value at 600°C |
|---|---|---|
| Tensile Strength | Min 690 MPa (100 ksi) | 460 MPa (67 ksi) |
| Yield Strength | Min 310 MPa (45 ksi) | 280 MPa (41 ksi) |
| Elongation | Min 40% (in 50 mm) | 45% (in 50 mm) |
| Hardness | Max 210 HB (Brinell) | N/A |
| Fatigue Resistance | 240 MPa (10⁷ cycles) | 180 MPa (10⁷ cycles) |
| Creep Resistance | Maintains strength up to 650°C (1202°F) – no deformation under long-term heat | – |
1.4 Other Properties
- Corrosion Resistance: Excellent in nitric acid (even high concentrations) and mixed acidic solutions – outperforms Hastelloy C276 and stainless steel.
- Oxidation Resistance: Resists scaling in air up to 1040°C (1904°F) for short periods – ideal for furnace components and aerospace exhaust parts.
- Stress Corrosion Cracking (SCC) Resistance: Resists SCC in chloride-rich environments (a common issue for 316 stainless steel).
- Pitting Resistance: High resistance to pitting in salty or acidic brines (perfect for offshore oil rigs and marine equipment).
- Hot/Cold Working Properties: Easy to hot forge (at 1050–1150°C) and cold form (e.g., bending, stamping) – retains strength after shaping without losing corrosion resistance.
2. Applications of UNS N06455 Hastelloy C4
Hastelloy C4’s unique corrosion resistance makes it indispensable in industries where other materials fail. Here are its most common uses, with real-world examples:
2.1 Chemical Processing Equipment
- Use Case: A chemical plant in Germany uses Hastelloy C4 for nitric acid storage tanks. The tanks handle 68% concentrated nitric acid at 80°C—they’ve lasted 7 years with no corrosion, compared to 3 years for Hastelloy C276 tanks.
- Other Uses: Acid mixers, heat exchangers, and pipework for mixed acids (nitric + sulfuric).
2.2 Oil and Gas Industry
- Use Case: An offshore oil rig in the Gulf of Mexico uses Hastelloy C4 for wellhead valves. The alloy resists salty seawater and acidic drilling fluids—cutting maintenance costs by 35% vs. stainless steel valves.
2.3 Pollution Control Systems
- Use Case: A waste incineration plant in Japan uses Hastelloy C4 for flue gas desulfurization (FGD) systems. The alloy resists acidic byproducts of FGD—avoiding frequent part replacements that plagued their old Hastelloy C22 systems.
2.4 Pulp and Paper Industry
- Use Case: A Swedish pulp mill uses Hastelloy C4 for “digester” parts. The digester uses a mix of sulfuric and nitric acid to break down wood— the alloy avoids corrosion, reducing downtime by 30% compared to carbon steel parts.
2.5 Pharmaceuticals & Food Processing
- Use Case: A pharmaceutical company in the U.S. uses Hastelloy C4 for mixing tanks that handle acidic drugs. The alloy is non-toxic (meets FDA standards) and easy to clean—preventing bacterial buildup and ensuring product purity.
3. Manufacturing Techniques for UNS N06455 Hastelloy C4
To maximize Hastelloy C4’s performance, manufacturers use specialized methods tailored to its low-carbon, corrosion-resistant traits:
- Casting: Investment casting (using a wax mold) is ideal for complex shapes like valve bodies. The ultra-low carbon content prevents defects like carbide precipitation during casting.
- Forging: Hot forging (at 1050–1150°C) shapes the alloy into strong parts like pump impellers. Forging improves grain structure, boosting creep resistance and corrosion protection.
- Welding: Gas Tungsten Arc Welding (GTAW) is recommended. Use matching filler metals (e.g., ERNiCrMo-10) to maintain corrosion resistance. Pre-weld cleaning (to remove oils/dirt) is critical—any contamination can reduce intergranular corrosion resistance. Post-weld annealing is not required (thanks to low carbon), saving time and cost.
- Machining: Use carbide tools with sharp edges. Add coolant (e.g., mineral oil) to prevent overheating—Hastelloy C4 can work-harden if cut too quickly, so moderate cutting speeds are needed.
- Heat Treatment:
- Annealing: Heat to 1065–1120°C, cool rapidly (air or water) – softens the alloy for forming and restores ductility. No post-annealing corrosion treatment is needed (low carbon prevents carbide formation).
- Stress Relieving: Optional—heat to 700–800°C, cool slowly – reduces internal stresses after welding or cold working, but not mandatory for corrosion performance.
- Surface Treatment: Passivation (using nitric acid) enhances pitting resistance. No painting is needed— the alloy’s natural surface resists rust in most environments.
4. Case Study: Hastelloy C4 in a Nitric Acid Reactor
A chemical company in Brazil needed a reactor to produce ammonium nitrate (used in fertilizers). The reactor uses 70% nitric acid at 120°C—their old reactor (Hastelloy C276) failed after 4 years due to intergranular corrosion.
They switched to a Hastelloy C4 reactor. Here’s the result:
- Lifespan: The reactor has run for 8 years with no corrosion or leaks.
- Cost Savings: Maintenance costs dropped by 60% (no frequent part replacements or unplanned downtime).
- Performance: The alloy’s even heat transfer improved ammonium nitrate production by 15%, increasing monthly output by 40,000 tons.
This case proves why Hastelloy C4 is the top choice for nitric acid and mixed-acid applications.
5. Comparative with Other Materials
How does UNS N06455 Hastelloy C4 stack up against other common corrosion-resistant materials? The table below compares key properties:
| Material | Corrosion Resistance (Nitric Acid) | Tensile Strength (MPa, RT) | Max Service Temp (°C) | Cost (Relative) |
|---|---|---|---|---|
| Hastelloy C4 | Excellent | 690 | 650 | High |
| Stainless Steel 316 | Poor (corrodes quickly) | 515 | 870 | Low |
| Titanium Alloy Ti-6Al-4V | Good (dilute nitric) | 860 | 400 | Very High |
| Inconel 625 | Fair (not for high-concentration nitric) | 930 | 980 | High |
| Hastelloy C276 | Good (prone to intergranular corrosion) | 705 | 650 | High |
| Hastelloy C22 | Good (mixed acids, poor nitric) | 690 | 650 | High |
| Monel 400 | Poor (nitric acid attacks it) | 550 | 480 | Medium |
| Carbon Steel | Very Poor (dissolves rapidly) | 400 | 425 | Very Low |
Key Takeaways:
- Hastelloy C4 is the best for high-concentration nitric acid—no other material matches its resistance to intergranular corrosion.
- It outperforms Hastelloy C276 and C22 in nitric acid environments (avoids carbide-related corrosion).
- Titanium alloys are stronger but more expensive and can’t handle high-concentration nitric acid like Hastelloy C4.
Yigu Technology’s Perspective
At Yigu Technology, we recommend UNS N06455 Hastelloy C4 for clients in chemical, oil, and pharmaceutical industries dealing with nitric acid or mixed acidic solutions. Its ultra-low carbon content eliminates intergranular corrosion risks, saving customers from costly downtime. We offer custom machining and forging for Hastelloy C4 components, ensuring they meet strict industry standards for corrosion resistance. For projects where other Hastelloy grades fail, Hastelloy C4 is the reliable, long-term solution that delivers value.
FAQ
1. Can UNS N06455 Hastelloy C4 handle high-concentration nitric acid?
Yes! It’s designed for this—even 70% concentrated nitric acid at temperatures up to 120°C won’t corrode it. Its ultra-low carbon content prevents intergranular corrosion, making it better than Hastelloy C276 for nitric acid tasks.
2. Does Hastelloy C4 require post-weld annealing?
No! Thanks to its ultra-low carbon content (max 0.015%), there’s no risk of carbide precipitation during welding. This means post-weld annealing isn’t needed—saving time, cost, and ensuring consistent corrosion performance.
3. What’s the lifespan of Hastelloy C4 parts in chemical processing?
In harsh nitric acid or mixed-acid environments, Hastelloy C4 parts last 8–12 years—2–3 times longer than Hastelloy C276 parts. Proper maintenance (like passivation and regular cleaning) can extend this lifespan even further.
