Incoloy 925 (UNS N09925) machines like a high-strength nickel alloy, it work-hardens rapidly, generates hot stringy chips, and demands rigid tooling with positive rake angles. The alloy is best machined in the solution-annealed condition (~92 HRB) before final ageing; once aged to ~32–35 HRC, machining becomes 3–5× slower and tool wear accelerates. The data below is taken from Special Metals Table 13 and is the authoritative starting point for production CNC programs. TorqBolt machines Incoloy 925 in both conditions on Mazak / Haas / DMG Mori turning centres with through-spindle coolant.
Need machined Incoloy 925 components? Email info@torqbolt.com with drawing / 3D model, tolerance requirements and surface-finish spec. WhatsApp +91-22-66157017.
Machining Speeds & Feeds, Solution Annealed (~92 HRB)
| Operation / Tool | Tool Material | Surface Speed, ft/min (m/min) | Feed, in/rev (mm/rev) | Depth of Cut, in (mm) |
|---|---|---|---|---|
| Turning, HSS | T-5 | 40–50 (12–15) | 0.030 (0.76) | 0.250 (6.4) |
| Turning, brazed carbide | C-6 | 175–225 (53–69) | 0.020 (0.51) | 0.150 (3.8) |
| Turning, indexable insert | C-2 / C-6 coated | 200–250 (61–76) | 0.020 (0.51) | 0.150 (3.8) |
| Drilling, HSS | M-7 | 20–30 (6–9) | 0.005–0.015 (0.13–0.38) | |
| Tapping, HSS | M-7 | 5–10 (1.5–3) | matching pitch | |
| Reaming, HSS | T-5 | 15–25 (5–8) | 0.010 (0.25) | |
| Milling (face), carbide | C-2 | 100–150 (30–45) | 0.005 per tooth | 0.100 (2.5) |
Machining Speeds & Feeds, Age-Hardened (~35 HRC)
| Operation / Tool | Tool Material | Surface Speed, ft/min (m/min) | Feed, in/rev (mm/rev) | Depth of Cut, in (mm) |
|---|---|---|---|---|
| Turning, HSS | M-36 | 15–20 (5–6) | 0.008 (0.20) | 0.050 (1.3) |
| Turning, brazed carbide | C-2 | 40–50 (12–15) | 0.008 (0.20) | 0.050 (1.3) |
| Turning, indexable insert | C-2 coated (TiAlN) | 50–100 (15–30) | 0.008 (0.20) | 0.050 (1.3) |
| Drilling, carbide | C-2 | 15–25 (5–8) | 0.003–0.008 (0.08–0.20) | |
| Tapping | HSS-Co or carbide | 3–6 (1–2) | matching pitch | |
| Milling (face), carbide | C-2 coated | 40–60 (12–18) | 0.003 per tooth | 0.030 (0.8) |
Source: Special Metals Corporation, INCOLOY® alloy 925 Technical Bulletin, Table 13. The age-hardened cutting parameters are roughly 1/3 of the annealed values, a strong argument for machining as much geometry as possible BEFORE the final age cycle.
Tool Geometry Recommendations
- Rake angle: +5° to +15° positive rake. Negative rake increases work-hardening and breaks tool tips.
- Relief angle: 6°–10°. Larger relief on aged material to reduce flank rub.
- Nose radius: 0.4–0.8 mm for finishing; 1.2–2.0 mm for roughing.
- Coating: TiAlN preferred for aged-condition machining (resists adhesion and extends tool life 2–3× vs uncoated). AlCrN for very high-temperature applications.
- Edge prep: Honed edge (15–25 μm radius) is more durable than sharp edge for interrupted cuts; sharp edge for finishing in annealed condition.
Coolant & Lubrication
Flood coolant is mandatory at high cutting forces. Through-spindle coolant at 800–1500 psi (55–100 bar) gives the best results for drilling deep holes and for inserting threading. Use:
- Synthetic coolant at 6–10% concentration in water, preferred for aged-condition turning where chip evacuation is critical.
- Soluble oil emulsion at 10–15% concentration, preferred for tapping, threading and broaching where lubricity matters.
- Sulphur-bearing cutting oils: Acceptable on annealed material but MUST be removed before age-cycle heat treatment, sulphur is a hot-cracking poison and any residual on the surface causes intergranular attack at 1900°F.
- Chlorine-bearing oils: NOT recommended for sour-service material, residual chlorine after de-greasing can pit the finished surface in service.
Work-Hardening Mitigation
Like all austenitic nickel alloys, Incoloy 925 work-hardens rapidly under deformation. A dull tool, dwelling at the cut, or excessive feed-rate variation creates a hardened surface layer that is 2–3× harder than the bulk and will destroy the next tool that engages it. Mitigations:
- Constant feed: Never dwell the tool in the cut. CNC programs should feed-out before stopping the spindle.
- Sharp tools: Index inserts at first sign of flank wear (typically 0.4 mm VB max). Dull tools rub instead of cut and create the work-hardened layer.
- Larger depth-of-cut than feed: Always cut below the previously-hardened layer. For finishing passes use depth > 0.005" minimum.
- Climb milling: Preferred over conventional milling because the chip starts thick and ends thin, leaving the harder surface inside the chip rather than the workpiece.
Surface Finish & Tolerance Capability
| Process | Achievable Surface Finish, Ra | Achievable Tolerance, IT class |
|---|---|---|
| Turning, finish pass (carbide) | 0.8–1.6 μm (32–63 μin) | IT7–IT8 |
| Grinding, cylindrical | 0.2–0.4 μm (8–16 μin) | IT5–IT6 |
| Honing | 0.05–0.2 μm (2–8 μin) | IT4–IT5 |
| Polishing | 0.025 μm (1 μin) | (form-following) |
Threading & Bolting Production
Most TorqBolt Incoloy 925 production is finished as stud bolts and heavy hex nuts for API 6A wellhead service. Thread cutting is performed in the SOLUTION-ANNEALED condition (annealed material is much more forgiving to single-point thread tools and chasers); the studs are then aged to final 32–35 HRC.
Thread rolling is preferred over thread cutting for fatigue-loaded fasteners, cold-rolled threads have residual compressive stress at the root that increases fatigue life by 2–3×. Roll dies must be hardened M-2 or M-7 HSS at HRC 60+; carbide rolls are NOT recommended (chip-out at thread root).
Frequently Asked Questions
Why machine in the annealed condition rather than aged? Aged Incoloy 925 (32–35 HRC) machines at roughly 1/3 the speed of annealed material with 3–5× the tool wear. Machining annealed then ageing is the standard production sequence: rough turn the bar in annealed condition, age to final hardness, then finish-grind / polish if needed. The age cycle is dimensionally stable (~0.001 in/in growth) so tight tolerances can be held.
Does the age cycle distort the part? Minimal distortion if the part is properly stress-relieved before ageing. Long, thin parts (long studs, long shafts) should be vertically suspended in the furnace with both ends free to grow. Box-shaped parts with rib geometry can warp 0.0005–0.002 in/in if heated unevenly, specify "stress-relief before age" at RFQ stage for tight-tolerance fabrications.
Can Incoloy 925 be EDM-machined? Yes, both wire-EDM and sinker-EDM work well. The recast layer must be removed for sour-service applications (typically 0.005–0.010 in stock removal by polishing or low-current finishing pass). EDM is preferred for complex internal geometry that is hard to access by conventional tooling.
What's the typical lead time for machined Incoloy 925 components? Bar/stock + machining: 4–6 weeks for standard sizes, 8–12 weeks for larger or non-standard sizes. The bottleneck is usually the 18-hour age cycle, furnace capacity is finite and ageing is performed in batches. See heat-treatment page for full age-cycle details.
Request a Quote
For machined Incoloy 925 components with full MTC documentation:
- Email: info@torqbolt.com
- WhatsApp: +91-22-66157017
- 2D drawing or 3D STEP file required for quoting
Specify drawing / 3D model, applicable standards (ASTM B805, ASTM B983, API 6A, NACE MR0175), required heat-treatment condition (annealed or aged), surface-finish spec (Ra), tolerance class, and any special inspection requirements (CMM report, surface dye-penetrant, magnetic permeability test for MWD applications).
References: Special Metals Corporation: INCOLOY® alloy 925 Technical Bulletin, Table 13. ASTM B805 Standard Specification for Forgings and Forging Stock for Nuclear and General Use Wrought Precipitation Hardened UNS N09925. ANSI / ASME B46.1 Surface Texture. INCOLOY® is a registered trademark of Special Metals Corporation.
