Inconel 625

Ⅱ. Chemical Composition (Mass Fraction, %)

• Nickel (Ni): Balance (≥58%)
• Chromium (Cr): 20.0 – 23.0
• Molybdenum (Mo): 8.0 – 10.0
• Niobium (Nb) + Tantalum (Ta): 3.15 – 4.15 (Tantalum is usually included in the total amount of niobium)
• Iron (Fe): ≤5.0
• Carbon (C): ≤0.10
• Silicon (Si): ≤0.50
• Manganese (Mn): ≤0.50
• Aluminum (Al) + Titanium (Ti): Each ≤0.40
• Cobalt (Co): ≤1.0
• Phosphorus (P), Sulfur (S): Both ≤0.015

3. Low – Temperature Properties

• -196°C (liquid nitrogen temperature): Fracture toughness is as high as 200 MPa√m, maintaining excellent toughness.

Ⅳ. Heat Treatment Requirements

1. Solution Treatment

• Temperature: \(980 – 1150^\circ\text{C}\) (commonly \(1040 – 1120^\circ\text{C}\))
• Holding Time: Adjusted according to thickness (e.g., 1 hour for plates, 2 hours for forgings)
• Cooling Method: Air cooling, water cooling or oil cooling (rapid cooling can avoid precipitation of harmful phases)
• Purpose: Dissolve carbides and intermetallic phases, optimize corrosion resistance and toughness.

2. Stress Relief Annealing

• Temperature: \(700 – 800^\circ\text{C}\) (when cold working deformation > 15%)
• Holding Time: 1 – 2 hours, air cooling
• Role: Eliminate processing stress and prevent cracking during subsequent use.

3. Special Treatment

• High – temperature aging: Long – term aging at \(650 – 900^\circ\text{C}\) can precipitate the γ” phase (\(\text{Ni}_3\text{Nb}\)), improving high – temperature strength, but plasticity needs to be balanced.

Ⅴ. Core Characteristics

1. Superb Corrosion Resistance:
   • Resists chloride pitting, crevice corrosion and stress corrosion cracking (such as in seawater, salt spray environments).
   • Resists corrosion by inorganic acids (nitric acid, sulfuric acid, hydrochloric acid) and mixed acids, with a corrosion rate < 0.188 mm/year in \(40^\circ\text{C}\) hydrochloric acid.
2. High – temperature Stability:
   • Oxidation resistance temperature reaches \(980^\circ\text{C}\), long – term service temperature ≤ \(650^\circ\text{C}\), and can reach \(1000^\circ\text{C}\) in the short term.
   • Forms a dense \(\text{Cr}_2\text{O}_3\) oxide film at high temperatures, inhibiting further oxidation.
3. Excellent Workability:
   • Good hot and cold formability, can be rolled, forged, stamped; excellent weldability, suitable for TIG/MIG welding, no special treatment required after welding.
4. Wide Temperature Range Adaptability:
   • Maintains stable mechanical properties from \(-196^\circ\text{C}\) to \(980^\circ\text{C}\), suitable for extreme temperature environments.

Ⅵ. Main Application Fields

1. Chemical and Petrochemical:
   • Chloride – containing reaction equipment (such as acetic anhydride generators), sulfuric acid condensers, acidic medium pipelines.
2. Marine Engineering:
   • Seawater desalination equipment, deep – sea detector components, offshore platform structural parts (resistant to seawater corrosion and high hydrostatic pressure).
3. Aerospace:
   • Aeroengine combustion chambers, turbine blades, high – temperature fasteners; rocket fuel pipelines.
4. Environmental Protection and Energy:
   • Absorption towers and reheaters of flue gas desulfurization (FGD) systems; nuclear reactor heat exchangers (resistant to radiation and corrosion).
5. Emerging Fields:
   • Waste – to – energy equipment, biofuel production devices (resistant to high – temperature corrosion).
6. Papermaking and Metallurgy:
   • Pulp digesters, bleaching tanks (resistant to chlorine and organic acids); high – temperature furnace rolls, corrosion – resistant fixtures.

Ⅶ. Industry Certifications and Specifications

• NACE MR0175/ISO 15156: Passed the highest – level certification (Level VII) for acidic gas environments (such as H₂S).
• ASME BPVC: Used in the manufacture of pressure vessels at \(-196 – 450^\circ\text{C}\).