Inconel 718 remains one of the most challenging materials to machine in modern manufacturing. As a precipitation-hardened nickel-based superalloy, it combines exceptional high-temperature strength with poor thermal conductivity, creating extreme cutting zone temperatures and rapid tool wear. This guide provides a detailed technical comparison of Korloy and Tungaloy turning insert grades specifically engineered for Inconel 718 machining, including verified cutting parameters and practical optimization strategies.
Material Characteristics and Machining Challenges
Inconel 718 (UNS N07718, W.Nr. 2.4668) exhibits properties that directly impact cutting tool performance:
- Tensile strength: 1,240 MPa (solution treated), up to 1,400 MPa (aged condition)
- Hardness: 36-47 HRC depending on heat treatment state
- Thermal conductivity: 11.4 W/m·K at 100°C (approximately 10% of carbon steel)
- Work hardening rate: High; surface hardness can increase 10-15% after initial cutting pass
- Cutting temperature: Frequently exceeds 1,000°C at the tool tip during continuous turning
These characteristics demand cutting tools with superior hot hardness, chemical stability, and optimized edge geometries to manage heat generation and chip control simultaneously.
Korloy Turning Solutions for Inconel 718
Recommended Grades
Korloy has developed several CVD and PVD-coated carbide grades targeting nickel-based superalloy applications:
- PC8110 (PVD TiAlN-based): General-purpose turning of Inconel 718 at moderate speeds. Balanced wear resistance and toughness for interrupted cuts.
- PC5300 (CVD Al₂O₃/TiCN): High-speed continuous turning applications. The alumina outer layer provides excellent crater wear resistance at elevated temperatures.
- PC9030 (PVD nano-multilayer): Finishing to medium-roughing operations. Enhanced edge stability for precision components in aerospace applications.
Chipbreaker Geometries
- MF (Medium Feed): Feed range 0.15-0.35 mm/rev, depth of cut 0.5-3.0 mm
- MR (Medium Roughing): Feed range 0.20-0.45 mm/rev, depth of cut 1.0-5.0 mm
- LF (Light Finishing): Feed range 0.05-0.20 mm/rev, depth of cut 0.1-1.5 mm
Tungaloy Turning Solutions for Inconel 718
Recommended Grades
Tungaloy’s portfolio for heat-resistant superalloys includes several standout performers:
- AH8015 (PVD TiSiAlN): Premium grade for continuous and light interrupted turning. Exceptional crater and flank wear resistance at high cutting speeds.
- AH725 (PVD TiAlN): Versatile grade suitable for both roughing and finishing. Strong performance in aerospace shaft and disk applications.
- T3130 (CVD Al₂O₃/TiCN): Heavy roughing grade for high material removal rates. Designed to withstand mechanical shock and thermal cycling.
Chipbreaker Geometries
- TSF (Tungaloy Standard Finishing): Feed 0.08-0.25 mm/rev, optimized for surface finish requirements Ra 0.8-1.6 µm
- TMF (Tungaloy Medium Feed): Feed 0.15-0.40 mm/rev, general-purpose chip control for bar turning
- THF (Tungaloy Heavy Feed): Feed 0.30-0.60 mm/rev, maximum productivity in roughing operations
Head-to-Head Grade Comparison
| Parameter | Korloy PC8110 | Korloy PC5300 | Tungaloy AH8015 | Tungaloy AH725 |
|---|---|---|---|---|
| Coating Technology | PVD TiAlN | CVD Al₂O₃/TiCN | PVD TiSiAlN | PVD TiAlN |
| Substrate Toughness | High | Medium-High | Medium | High |
| Optimal Vc (m/min) | 25-40 | 35-55 | 30-50 | 25-45 |
| Max Cutting Temp Tolerance | ~950°C | ~1,050°C | ~1,100°C | ~980°C |
| Primary Wear Mode | Flank wear, notch wear | Crater wear | Flank wear | Flank wear, edge chipping |
| Application Type | General, interrupted | High-speed continuous | High-speed continuous | Versatile roughing/finishing |
| Typical Tool Life (min) | 12-18 | 15-22 | 18-28 | 14-20 |
Recommended Cutting Parameters
Continuous External Turning (Aged Inconel 718, 42-47 HRC)
| Operation | Insert Grade | Vc (m/min) | f (mm/rev) | ap (mm) | Coolant Strategy |
|---|---|---|---|---|---|
| Roughing | Korloy PC5300 / Tungaloy T3130 | 30-40 | 0.25-0.35 | 2.0-4.0 | High-pressure (70-100 bar) |
| Semi-finishing | Korloy PC8110 / Tungaloy AH725 | 35-45 | 0.15-0.25 | 1.0-2.0 | Through-tool + flood |
| Finishing | Korloy PC9030 / Tungaloy AH8015 | 40-55 | 0.08-0.15 | 0.3-1.0 | Through-tool precision |
| High-speed finishing | Tungaloy AH8015 | 50-65 | 0.06-0.12 | 0.2-0.5 | Minimum quantity lubrication (MQL) |
Interrupted Turning / Cast Surfaces
| Operation | Insert Grade | Vc (m/min) | f (mm/rev) | ap (mm) |
|---|---|---|---|---|
| Heavy roughing | Korloy PC8110 | 20-28 | 0.30-0.40 | 3.0-5.0 |
| Medium roughing | Tungaloy AH725 | 22-32 | 0.20-0.30 | 2.0-4.0 |
Tool Life Optimization Strategies
1. Cutting Speed Selection
For Inconel 718, cutting speed has the most significant impact on tool life. A 20% increase in Vc typically reduces tool life by 40-50%. For optimal economy, select the lowest Vc that meets productivity targets. Korloy PC5300 and Tungaloy AH8015 allow higher speed windows (up to 55 m/min) while maintaining acceptable tool life through advanced coating thermal barriers.
2. Feed Rate and Depth of Cut
Higher feed rates (above 0.30 mm/rev) increase chip thickness, which actually reduces specific cutting energy and lowers interface temperature per unit volume. However, excessive feed accelerates notch wear at the depth-of-cut line. Recommended balanced parameters:
- Roughing: f = 0.28-0.35 mm/rev, ap = 2.5-3.5 mm
- Finishing: f = 0.10-0.15 mm/rev, ap = 0.5-0.8 mm
3. Coolant Application
High-pressure coolant (70-150 bar) directed precisely at the cutting zone is critical for Inconel 718. Benefits include:
- Temperature reduction of 150-250°C at the tool-chip interface
- Improved chip breaking and evacuation
- Reduced built-up edge (BUE) formation
- Extended tool life by 30-60% compared to flood coolant alone
Both Korloy and Tungaloy insert geometries are designed with coolant channel compatibility. Ensure through-tool coolant delivery when possible.
4. Edge Preparation
For Inconel 718, edge honing (T-land or radius) is essential to prevent micro-chipping:
- Finishing (f < 0.15 mm/rev): Honed edge 0.02-0.05 mm, 15° T-land
- General (f 0.15-0.30 mm/rev): Honed edge 0.05-0.10 mm, 20° T-land
- Roughing (f > 0.30 mm/rev): Honed edge 0.08-0.15 mm, 25° T-land
Tungaloy AH8015 and Korloy PC9030 are often available with “E” (sharp) and “G” (reinforced) edge preparations to match application severity.
5. Tool Overhang and Rigidity
Inconel 718’s high cutting forces demand maximum system rigidity:
- Keep tool overhang to minimum (L/D < 4 for boring, < 6 for external turning)
- Use hydraulic or shrink-fit holders for best damping
- Ensure spindle runout < 0.005 mm at tool tip
Surface Finish and Dimensional Accuracy
Achieving Ra 0.8-1.6 µm on Inconel 718 requires attention to multiple variables beyond insert grade:
- Nose radius: 0.4-0.8 mm for general finishing; 0.2-0.4 mm for tight tolerances
- Lead angle: 93°-95° tool holders minimize radial forces and deflection
- Wiper inserts: Both Korloy (WW chipbreaker) and Tungaloy (W finishing geometry) offer wiper options for superalloy finishing
| Insert Specification | Expected Surface Finish Ra (µm) | Recommended Application |
|---|---|---|
| CNMG 120404-MF (Korloy PC9030) | 0.8-1.2 | General aerospace finishing |
| CNMG 120408-TMF (Tungaloy AH8015) | 0.6-1.0 | High-precision shaft finishing |
| DNMG 150604-LF (Korloy PC9030) | 1.0-1.6 | Medium finishing, larger components |
| TNMG 160404-TSF (Tungaloy AH8015) | 0.8-1.4 | Taper and contour finishing |
Practical Selection Guide
Choose Korloy when:
- Interrupted cuts, cast skin, or forging scale are present
- High substrate toughness is prioritized over maximum speed
- CVD-coated grades (PC5300) are preferred for heavy continuous roughing
- Cost per edge is a primary consideration
Choose Tungaloy when:
- Maximum cutting speed and productivity are required
- Superior surface finish on continuous surfaces is critical
- AH8015’s TiSiAlN coating provides the thermal barrier needed for high-speed aerospace work
- Advanced chipbreaker geometries (TSF/TMF) are needed for demanding chip control
Conclusion
Both Korloy and Tungaloy offer technically capable solutions for Inconel 718 turning. Tungaloy AH8015 leads in high-speed continuous applications with its advanced TiSiAlN coating, delivering tool life up to 28 minutes at Vc 50 m/min. Korloy PC5300 provides excellent crater wear resistance for continuous roughing, while Korloy PC8110 offers superior toughness for interrupted conditions.
For most aerospace manufacturers, maintaining a dual inventory of Tungaloy AH8015 for finishing and high-speed work, paired with Korloy PC8110 or PC5300 for roughing and interrupted cuts, provides the optimal balance of performance, reliability, and cost efficiency.
Always verify parameters with your machine tool capability, workpiece configuration, and coolant system before full production implementation. Conduct tool life testing at the lower end of recommended speed ranges and optimize upward based on measured wear progression.
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