Inconel 625 Superalloy
Comprehensive technical specification for Inconel 625 (UNS N06625) superalloy, covering Canadian stock sizing, machinability, tooling, common defects, and handling guidelines for industrial fabrication and machining operations.
Material Overview & Common Uses
Inconel 625 is a nickel-chromium-molybdenum superalloy (UNS N06625) known for exceptional corrosion resistance, high tensile strength (up to 120 ksi / 827 MPa), and excellent oxidation resistance up to 1000°C (1832°F). It is widely used in Canadian aerospace, chemical processing, marine engineering, and oil & gas extraction (e.g., downhole tubing, heat exchangers, exhaust systems). The alloy work-hardens rapidly, requiring specialized tooling and rigid setups. Common forms include sheet, plate, round bar, and pipe, typically sourced in annealed or solution-treated condition.
Core Technical Properties & Sizing
| Parameter | Specification |
|---|---|
| Density | 8.44 g/cm³ (0.305 lb/in³) |
| Melting Range | 1290–1350°C (2350–2460°F) |
| Tensile Strength (Annealed) | 827–1034 MPa (120–150 ksi) |
| Yield Strength (0.2% offset) | 345–690 MPa (50–100 ksi) |
| Elongation | 30–60% in 2 in. |
| Hardness | 145–220 HB (annealed); work-hardened up to 350 HB |
| Thermal Conductivity | 9.8 W/m·K at 20°C |
| Electrical Resistivity | 1.29 µΩ·m |
| Standard Sheet/Plate Sizes | 48" x 96" (4x8 ft), 48" x 120" (4x10 ft), 60" x 120" (5x10 ft) |
| Thickness Range | 0.016" (0.4 mm) to 0.500" (12.7 mm) |
| Round Bar Sizes | 1/4" to 12" diameter, 12' or 20' lengths |
| Thickness Tolerances (ASTM B443) | ±0.005" for <0.060", ±0.007" for 0.060–0.125", ±0.010" for 0.126–0.250", ±0.015" for 0.251–0.500" |
| Flatness | 1/4" per 48" length |
| Surface Finish | Mill finish (2B) or bright annealed (BA) – typical Ra 0.5–1.5 µm |
Machinability, Tooling & Feeds
| Parameter | Recommendation |
|---|---|
| Machinability Rating | ~15% of free-machining steel (poor) |
| Tool Material (Roughing) | Carbide C2–C5 with TiAlN / AlTiN coatings |
| Tool Material (Finishing) | Ceramic (SiAlON) or CBN inserts |
| Geometry | Positive rake, rigid setup |
| Coolant | High-pressure flood or through-tool |
| Turning Speed (Carbide) | 30–60 SFM (9–18 m/min) |
| Turning Feed | 0.004–0.012 in/rev (0.10–0.30 mm/rev) |
| Turning Depth of Cut | 0.020–0.100 in (0.5–2.5 mm) |
| Milling Speed | 20–40 SFM (6–12 m/min) |
| Milling Chip Load | 0.002–0.006 in/tooth (0.05–0.15 mm/tooth) |
| Drilling Speed | 10–20 SFM (3–6 m/min) |
| Drilling Method | Peck cycle recommended |
| Threading | Rigid tapping or thread milling; avoid roll forming |
| Common Floor Defects | Edge burring, built-up edge (BUE), chatter, surface tearing |
Common Defects & Quality Control
| Defect / Inspection | Description / Criteria |
|---|---|
| Surface Laps & Seams | Check on bar stock; reject if visible |
| Delamination / Edge Cracking | Inspect on sheared plate |
| Camber / Twist | Excessive in long lengths |
| Inconsistent Hardness | Indicates improper heat treatment |
| Work-Hardened Spots | Can cause tool breakage during machining |
| Built-Up Edge (BUE) | Leads to poor surface finish |
| Thermal Cracking | From inadequate coolant |
| Surface Roughness | Ra ≤ 1.6 µm for functional surfaces |
| Intergranular Attack / Pitting | Reject; test per ASTM G28 |
| Dimensional Checks | Micrometers and CMM; verify flatness on surface plate |
Storage, Handling & Racking Guidelines
Store indoors in a dry, climate-controlled environment (humidity <50% RH) to prevent surface oxidation. Keep away from chlorides and sulfides (e.g., in marine environments). Use dedicated racks with padded or wooden supports to avoid scratching; separate sheets with kraft paper or plastic interleaving. For bar stock, use horizontal racks with full-length support to prevent bending.
- Handle with clean gloves; avoid steel-to-steel contact to prevent galling.
- Lifting: use spreader bars for large sheets; never drag across floor.
- Inventory rotation: FIFO recommended; label with heat number and date received.
- For long-term storage, apply a light oil film or VCI paper.