NC6948 Nimonic C-263 Bar

Nimonic C-263 Bars Description

The Nimonic C-263 bars contain a γ‐austenite matrix strengthened by ordered γ' precipitates (Ni₃[Al, Ti]). These precipitates represent 25–30 vol% and have an average size of 20–50 nm after a solution treatment at 1 150°C and ageing at 800°C for 8 hours.

Chromium‐rich M₂₃C₆ carbides form along the grain boundaries (<1 vol%), whereas Mo/Ti‐rich MC carbides, at less than 0.5 vol%, impart dispersion strengthening. The creep resistance has been measured at 100 MPa stress rupture at 800°C for 100 hours. This performance is achieved through γ' coherency strains that inhibit dislocation climb and through solid‐solution strengthening contributed by cobalt and molybdenum.

Under thermal conditions, the bars maintain phase stability up to 900°C with σ‐phase formation remaining below 0.3 vol% after 1 000 hours. This stability is due to a controlled aluminium/titanium ratio (Al/Ti ≈ 0.7). The coefficient of thermal expansion is 14.8 μm/m·°C over 20–800°C, while the thermal conductivity increases from 11.5 W/m·K at 20°C to 26.3 W/m·K at 800°C. After solution treatment, the bars attain an ultimate tensile strength of between 950 and 1 100 MPa, a yield strength of 650–750 MPa, and an elongation of 25–30%; they retain 85% of yield strength at 800°C.

Oxidation resistance arises from the formation of a continuous Cr₂O₃ scale, with a parabolic rate constant kp = 3×10⁻¹⁴ g²/cm⁴·s at 900°C. Titanium doping enhances scale adhesion. Electrochemical behaviour indicates an anodic dissolution rate of less than 10⁻⁷ A/cm² in 3.5% NaCl at 600°C because of Mo‐stabilised passivity. Fatigue strength at 800°C exceeds 300 MPa during 10⁷ cycles (R = –1). The alloy avoids strain‐age cracking during welding as the γ' solvus is controlled at 1 020°C and the misfit strain remains low (δ = 0.2%).

Nimonic C-263 Bars Applications

The Nimonic C-263 bars are employed in thermomechanical environments that require high-temperature strength, corrosion resistance and machinability. Their primary application is in aerospace gas turbine combustors and afterburner liners. The γ' precipitate hardening offers creep strength above 100 MPa at 800°C and resists thermal fatigue during repeated thermal cycles. A controlled Al/Ti ratio permits welded construction of complex hot-section components without strain-age cracking.

In power generation, the bars are used to fabricate transition ducts and seals in land-based gas turbines operating at 815–870°C. The chromium oxide scale, with kp = 3×10⁻¹⁴ g²/cm⁴·s at 900°C, resists oxidation-carburisation. In ultra-supercritical coal-fired plants, the alloy is employed for boiler tubes and steam headers operating at 700–750°C and 35 MPa; cobalt solid-solution strengthening sustains a yield strength above 450 MPa after 100 000 hours.

Petrochemical applications include reactor vessels that handle sulphuric or phosphoric acids at temperatures not exceeding 200°C. In these conditions, the molybdenum content (5.6–6.1%) increases resistance to pitting when chloride contaminants are present. The nuclear sector utilises the material for fuel reprocessing tubing in nitric acid/nitrate solutions; this is based on the stability of the passive film under gamma irradiation. Industrial applications further include high-strength fasteners for geothermal systems exposed to H₂S/CO₂ brines, paper and pulp bleaching rollers that withstand sulphide corrosion and centrifugal compressor impellers for sour gas injection.

The alloy is also applied in marine turbine exhaust systems, where saltwater pitting is minimised, and in catalyst regeneration units that operate under cyclic oxidation at 750°C. The material retains 85% of its room-temperature yield strength at 800°C and permits conventional machining. Its measured performance justifies its selection in situations where failure consequences are severe despite its higher cost.

Nimonic C-263 Bars Packaging

Products are packaged in customised cartons of various sizes depending on the material dimensions. Small items are placed in PP boxes, while larger items are secured in custom wooden crates. Packaging customisation is followed accurately and appropriate cushioning materials are utilised to provide optimal protection during transport.

Packaging: Carton, Wooden Box, or Customized.

Kindly review the packaging details provided for your reference.

Manufacturing Process

1.       Testing Method

(1)    Chemical Composition Analysis – GDMS or XRF techniques are employed to verify that the composition complies with the required purity levels.

(2)    Mechanical Properties Testing – Tensile strength, yield strength and elongation tests are performed to assess the material’s performance.

(3)    Dimensional Inspection – Measurements of thickness, width and length are conducted to ensure the dimensions meet specified tolerances.

(4)    Surface Quality Inspection – Visual and ultrasonic examinations are carried out to check for defects such as scratches, cracks or inclusions.

(5)    Hardness Testing – The tests determine the material’s hardness to confirm uniformity and mechanical reliability.

Please refer to the SAM testing procedures for further details.

Nimonic C-263 Bars FAQs

Q1. What maximum continuous service temperature avoids significant γ' coarsening?

γ' precipitates remain below 50 nm in size when the temperature is maintained under 850°C. Prolonged exposure above 850°C results in precipitate growth to over 100 nm after 1 000 hours, reducing creep strength by 25–30%. For service above 850°C, exposure should be limited to under 500 hours.

Q2. How does welding thermal cycling affect aged microstructure?

The heat-affected zone reaches temperatures above 1 020°C (the γ' solvus), which dissolves the precipitates. On cooling, reprecipitation may induce strain-age cracking unless the interpass temperature is maintained below 100°C and a post-weld ageing at 800°C for 8 hours is applied to restore 95% of the heat-affected zone strength.

Q3. Are there specific machining parameters to avoid work hardening?

Yes:

Turning – Carbide tools must be used at speeds of 25–35 m/min with a feed rate of at least 0.15 mm/rev.

Drilling – A 70° point angle is recommended and peck drilling should be executed every two times the drill diameter.

Coolant must be sulphur-free in order to prevent the initiation of stress corrosion.

Related Information

1.       Common Preparation Methods

Nimonic C-263 bars are produced using a multi‐stage thermomechanical and thermal processing sequence. The process begins with vacuum induction melting (VIM) of high‐purity raw materials – including electrolytic nickel, chromium pellets, cobalt granules, molybdenum powder and master alloys of aluminium/titanium – under an argon atmosphere. This process obtains precise compositional control (Ni balance, Cr 20±0.5%, Co 20±0.5%, Mo 6±0.2%, Al 0.4±0.1%, Ti 2.2±0.1%). The molten alloy is then refined using electroslag remelting (ESR) or vacuum arc remelting (VAR) to reduce interstitial elements (O ≤ 30 ppm, N ≤ 80 ppm) and eliminate macro‐segregation. Ingots with diameters ranging from 300 to 600 mm are subsequently homogenised at 1 200°C for 12–24 hours to dissolve primary carbides. Hot forging is then performed within the γ‐austenite stability range (1 150–1 200°C) with a minimum reduction ratio of 5:1 to refine the as‐cast structure. Hot rolling is conducted at 1 100–1 150°C, progressively reducing the cross-section to form intermediate billets with diameters between 50 and 150 mm, while maintaining controlled strain rates of 0.05–0.5 s⁻¹ to prevent edge cracking associated with aluminium/titanium segregation.

A solution treatment at 1 150±10°C for 2–4 hours per 100 mm of diameter dissolves the γ' precipitates (Ni₃[Al, Ti]) and M₂₃C₆ carbides. This is followed by rapid water quenching to retain a supersaturated solid solution. Cold working (via drawing or swaging) then imposes a 20–40% reduction in cross-section to achieve near-net dimensions, with intermediate solution annealing after each 30% reduction to mitigate work hardening. A two-stage ageing process is applied: primary ageing at 800±10°C for 8 hours precipitates fine γ' particles (20–50 nm diameter, 25–30 vol%), followed by secondary ageing at 700±10°C for 16 hours to stabilise M₂₃C₆ grain boundary carbides without compromising γ' coherency. Microstructural control is maintained by achieving a grain size in the ASTM 5–8 range (15–40 μm) and by preventing TCP phase formation (σ, μ) through limiting exposure in the 750–950°C range to under 15 minutes during cooling cycles. Final machining is carried out using ceramic or carbide tools with sulphur-free coolants to meet dimensional tolerances (ISO h9), while electrochemical polishing is performed to obtain a surface roughness of Ra ≤0.8 μm. Non-destructive testing includes ultrasonic testing for internal flaws greater than 0.5 mm, eddy current inspection for surface defects exceeding 50 μm, and metallographic verification of the γ' distribution using TEM or SEM. Thermomechanical performance is validated via stress rupture testing at over 100 MPa at 800°C for 100 hours and Charpy V-notch impact testing exceeding 40 J at 20°C.