Hastelloy C22
Complete analysis of Hastelloy C22 alloy (UNS N06022)
I. Implementation standards (classified by product form)
The technical specifications of Hastelloy C22 cover American standards (ASTM/ASME), European standards and national standards, targeting different product forms:
- Plates/strips: ASTM B575 / ASME SB – 575 (specifies chemical composition, mechanical properties and dimensional tolerances);
- Bars/forging billets: ASTM B574 / ASME SB – 574 (bars), ASTM B564 / ASME SB – 564 (forgings);
- Seamless pipes: ASTM B622 / ASME SB – 622;
- Welded pipes: ASTM B619 / ASME SB – 619, ASTM B366 / ASME SB – 366 (corrosion – resistant welded pipes).
II. Name and Code
- General name: Hastelloy C22;
- Authoritative identification:
- American standard: UNS N06022 (core number, unique general identifier);
- European standard: W.Nr. 2.4602 (Germany), NiCr21Mo14W3 (component abbreviation, highlighting the content of Cr, Mo, W);
- National standard: NS3308 (corresponding grade 00Cr22Ni60Mo13W3, nickel – based corrosion – resistant alloy);
- Commercial aliases: HC – 22, INCONEL Alloy C – 22, Nicrofer 5621 hMoW – Alloy C – 22, etc.
III. Chemical composition (mass fraction,%, typical range of ASTM standard)
Hastelloy C22 is a nickel – chromium – molybdenum – tungsten – based super corrosion – resistant alloy, which resists oxidation/reduction dual – medium corrosion through the synergy of “high Cr + Mo + W”. Its composition is as follows:
| Element | Content Range | Core Function |
|---|---|---|
| Nickel (Ni) | ≥56 (balance) | Stabilizes the austenitic matrix and resists stress corrosion |
| Chromium (Cr) | 20.0 – 22.5 | Resists oxidation (resists nitric acid, humid chlorine gas) and inhibits pitting corrosion |
| Molybdenum (Mo) | 12.5 – 14.5 | Resists reducing media (sulfuric acid, hydrochloric acid) and enhances resistance to crevice corrosion |
| Tungsten (W) | 2.5 – 3.5 | Strengthens resistance to chloride and humid chlorine gas corrosion, and improves local corrosion resistance |
| Iron (Fe) | 2.0 – 6.0 | Reduces cost and assists in strengthening |
| Cobalt (Co) | ≤2.5 | Impurity control (residual element, needs to be limited to avoid hot cracking) |
| Carbon (C) | ≤0.015 | Avoids carbide precipitation and prevents intergranular corrosion |
| Manganese (Mn) | ≤0.5 | Improves hot working fluidity |
| Silicon (Si) | ≤0.08 | Inhibits high – temperature oxidation and optimizes casting structure |
| Sulfur (S) | ≤0.02 | Inhibits hot working hot cracking tendency |
| Vanadium (V) | ≤0.35 | Refines grains and assists in strengthening (trace addition) |
IV. Mechanical properties (solid solution treatment state, typical value at room temperature)
After solution treatment (water quenching/air cooling at 1150 – 1175°C), Hastelloy C22 combines medium – high strength and ultra – high plasticity, and can be stably used at -200 – 400°C:
| Performance Indicator | Typical Value (Solution State) | Remarks |
|---|---|---|
| Tensile Strength | ≥690 MPa | Can be further improved by cold working (e.g., reaches 800 MPa + after cold rolling) |
| Yield Strength (0.2%) | ≥283 MPa | Some standards require ≥310 MPa (need to be combined with specifications) |
| Elongation (%) | ≥40 | Excellent formability, supporting complex processing (rolling, welding) |
| Hardness (HB) | ≤210 | No age hardening (the austenitic matrix is stable, and aging has limited improvement on performance) |
V. Heat Treatment Requirements
- Core Process: Solution Treatment
- Temperature: 1150 – 1175°C (hold for 1 – 2 hours to ensure uniform solid solution of Mo, W and Cr and inhibit the precipitation of harmful phases);
- Cooling: Rapid water quenching or air cooling (to prevent the precipitation of carbides/μ phases at grain boundaries and avoid the decrease of hot cracking resistance and corrosion resistance).
- Processing Auxiliary Points:
- Hot working: Temperature range 1150 – 1230°C (needs to quickly pass through the sensitization zone to avoid intergranular corrosion);
- Cold working: Easy to form in the solution state, it is recommended that the single deformation amount ≤30% (excessive cold working requires intermediate annealing to restore plasticity).
VI. Main application fields
Hastelloy C22, due to its “resistance to oxidation + reduction dual – medium corrosion + resistance to local corrosion”, focuses on extreme complex corrosion scenarios:
- Chemical Industry:
- Sulfuric acid/hydrochloric acid production: Evaporators, heat exchangers (resistant to dilute sulfuric acid at ≤80°C and concentrated hydrochloric acid corrosion, resistant to pitting corrosion by chlorides such as FeCl₃/CuCl₂);
- Mixed acid systems: (nitric acid + hydrochloric acid, sulfuric acid + hydrofluoric acid), resisting both oxidation and reduction corrosion at the same time.
- Environmental Protection Desulfurization:
- Flue gas desulfurization (FGD) system: (absorption towers, spray pipes, resistant to high Cl⁻ and SO₄²⁻ mixed corrosion, service life over 5 years, better than C276 in strong oxidizing environments).
- Marine Engineering:
- Seawater desalination membranes, offshore platform pipelines (resistant to seawater/salt spray, resistant to pitting/crevice corrosion, especially suitable for high Cl⁻ environments).
- Oil and Natural Gas:
- Acid gas field pipelines: (containing H₂S/CO₂/Cl⁻), crude oil distillation towers (resistant to high – temperature corrosion, resistant to sulfur corrosion).
- Special Scenarios:
- Pulp bleaching: (resistant to ClO₂ and chloride corrosion), pharmaceutical/food: (resistant to chemical cleaning agents and high – temperature sterilization, low C/Si avoids sensitization).
Supplementary Characteristics
- Corrosion resistance advantage: Compared with C276, it has a higher Cr content (20 – 22.5% vs 14.5 – 16.5% of C276), more resistant to strong oxidizing media such as humid chlorine gas and nitric acid, while maintaining the ability to resist reducing acids (sulfuric acid, hydrochloric acid); excellent resistance to stress corrosion cracking (SCC) and local corrosion (pitting, crevice corrosion).
- Weldability: ERNiCrMo – 10 welding wire (AWS A5.14) is recommended, and heat input should be controlled (≤1.5kJ/mm) to avoid hot cracking. The welded state still maintains high corrosion resistance (low C/Si inhibits intergranular precipitation).
- Limitation: Not resistant to molten strong alkali (such as NaOH ≥300°C) and strong oxidizing acids (such as concentrated nitric acid + high – concentration Fe³⁺), and such environments should generally be avoided.
Hastelloy C22 is a “benchmark alloy for oxidation – reduction dual corrosion”, and its core competitiveness lies in the synergy of high Cr + Mo + W to resist complex corrosion. When selecting materials, it is necessary to match standards and processing states based on medium type (oxidation/reduction proportion), temperature, and stress level.