Inconel 690

Introduction to Inconel 690

Inconel 690 is a high-chromium nickel alloy specifically engineered for superior corrosion resistance in aggressive aqueous and high-temperature environments, especially those involving sulfur-containing gases or strong oxidizers. It is widely recognized for its performance in heat exchangers, steam generators, and nuclear reactor tubing due to its excellent resistance to stress corrosion cracking and oxidation.

With a chemical composition centered on nickel (≥58%), chromium (27–31%), and iron (7–11%), Inconel 690 offers exceptional metallurgical stability and mechanical strength at elevated temperatures. This makes it a top choice for industries such as nuclear energy, petrochemical processing, and superheater systems.

Chemical, Physical, and Mechanical Properties of Inconel 690

Inconel 690 (UNS N06690 / W.Nr. 2.4642) meets the requirements of ASTM B167 and ASTM B564, and is especially suited for corrosive and oxidizing environments at high temperatures.

Chemical Composition (ASTM B167)

Physical Properties

Mechanical Properties (Annealed Condition – ASTM B167)

Key Characteristics of Inconel 690

• Oxidation Resistance: Superior performance in oxidizing atmospheres up to 1000°C, forming a tenacious chromium oxide layer that minimizes scaling and spalling under thermal cycling.

• Stress Corrosion Cracking Resistance: Especially resistant to intergranular attack and chloride-induced SCC, making it suitable for nuclear steam generator tubing and chemical plant use.

• Aqueous Corrosion Performance: Corrosion rate below 0.02 mm/year in boiling 10% nitric acid, and excellent resistance to caustic solutions (50% NaOH) and high-purity water.

• Thermal Stability: Grain boundary stability under long-term thermal exposure, minimizing carbide precipitation and intermetallic formation.

CNC Machining Challenges and Solutions for Inconel 690

Machining Challenges

Tool Degradation

• High chromium and nickel content promotes work hardening and introduces abrasive oxide inclusions that reduce tool life significantly.

Heat Generation

• Moderate thermal conductivity causes heat concentration at the cutting edge, leading to microchipping and poor surface quality.

Built-Up Edge Formation

• Ductile nature and strain rate sensitivity create adhesion and smearing at low speeds, affecting tolerances and finish.

Optimized Machining Strategies

Tool Selection

Cutting Parameters (ISO 3685)

Surface Treatment for Machined Inconel 690 Parts

Hot Isostatic Pressing (HIP)

HIP consolidates microvoids and removes internal porosity under 100–200 MPa gas pressure at 1100–1200°C, significantly enhancing creep strength and fatigue life in nuclear-grade components.

Heat Treatment

Heat Treatment stabilizes the microstructure post-machining. Solution annealing at 1065–1095°C followed by rapid cooling improves ductility and prepares the material for service temperatures above 900°C.

Superalloy Welding

Superalloy Welding using matching filler metals ensures tensile joint strength ≥95% of base metal. Precise arc control minimizes heat-affected zone degradation.

Thermal Barrier Coating (TBC)

TBC Coating applies 100–300 µm ceramic layers via plasma spray to reduce surface temperatures by up to 200°C, extending service life in turbine and boiler environments.

Electrical Discharge Machining (EDM)

EDM achieves ±0.01 mm tolerance and sub-Ra 0.4 µm finishes in heat-treated Inconel 690 components with minimal mechanical stress.

Deep Hole Drilling

Deep Hole Drilling enables drilling of L/D ratios up to 50:1, essential for steam generator tubing and heat exchanger manifolds.

Material Testing and Analysis

Material Testing includes ultrasonic, X-ray, and microstructural evaluation to ASTM E112 and E292 standards, ensuring internal integrity and performance reliability.

Industry Applications of Inconel 690 Components

Nuclear Power Generation

• Steam generator tubing, baffle plates, and heat exchangers.

• Performs under high-purity water and radiation exposure without embrittlement.

Chemical Processing

• Catalytic reformers, pickling equipment, and reboilers.

• Handles strong oxidizers, nitric/hydrochloric acid, and mixed-phase media.

Waste Incineration and Pollution Control

• Exhaust stack liners and thermal oxidizer components.

• Resists attack from SOx, NOx, and halogen-bearing combustion gases.

Superheaters and Boilers

• Furnace components, riser tubes, and high-pressure manifolds.

• Retains structural integrity under continuous high heat and pressure cycling.

FAQs

1. What cutting tools and coatings are best suited for CNC machining Inconel 690?

2. How does Inconel 690 perform in oxidizing chemical environments and high-pressure steam?

3. What surface treatments can improve the fatigue life of Inconel 690 parts?

4. Is Inconel 690 suitable for nuclear-grade and radiation-resistant components?

5. Can Neway machine and finish Inconel 690 parts to meet strict ASME or ASTM standards?