In advanced engineering fields such as oil and gas, aerospace, and power generation, nickel-based alloys are essential for their ability to resist corrosion, maintain strength at elevated temperatures, and deliver long-term reliability. However, one key challenge in working with these superalloys is machinability — how easily they can be cut, shaped, or drilled into final components.
Two alloys that are frequently compared for this purpose are Alloy N09935 and Alloy 718 (Inconel 718). Both offer remarkable mechanical performance, but their machinability characteristics differ significantly.
This article from SASAALLOY explores in detail how Alloy N09935 compares to Alloy 718 in terms of machinability, tooling behavior, chip formation, and productivity, helping manufacturers make informed decisions about material selection and production efficiency.
1. Understanding Alloy N09935 and Alloy 718
1.1 Alloy N09935 Overview
Alloy N09935 is a nickel-iron-chromium alloy that also contains molybdenum, copper, niobium, and titanium. It was designed to provide high strength combined with superior corrosion resistance, particularly in sour-gas (H₂S) and chloride-containing environments.
It is typically used in downhole oilfield components, tubular systems, valves, and chemical plant equipment, where both machinability and corrosion resistance are essential.
The alloy is precipitation-hardening but maintains good ductility and workability. Standards include ASTM B649 and compliance with NACE MR0175 / ISO 15156.
1.2 Alloy 718 Overview
Alloy 718 (UNS N07718), also known as Inconel 718, is a nickel-chromium-iron alloy strengthened by niobium and titanium. It is one of the most widely used superalloys due to its high tensile and creep-rupture strength up to 700°C, combined with excellent oxidation resistance.
However, the same strengthening mechanisms that make Alloy 718 extremely strong — primarily gamma prime (γ′) and gamma double prime (γ″) precipitation — also make it notoriously difficult to machine. The alloy work-hardens rapidly, generates high cutting forces, and tends to cause severe tool wear.
2. Machinability in Superalloys – The Core Challenge
Machinability is influenced by several metallurgical and mechanical factors:
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Work-hardening rate
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Thermal conductivity
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Abrasive carbides or intermetallics in the microstructure
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Cutting speed and tool geometry
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Surface integrity and heat generation
Nickel-based alloys, by nature, exhibit poor machinability because of their high strength, low thermal conductivity, and strong tendency to harden under tool pressure. The challenge lies in achieving good surface finish and dimensional accuracy without excessive tool wear or deformation.
3. Comparative Machinability: Alloy N09935 vs Alloy 718
3.1 Cutting Behavior
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Alloy 718 is considered one of the most difficult nickel alloys to machine. It work-hardens extremely fast, producing high tool stresses. During cutting, it often forms long, continuous chips that can damage the tool edge if not properly controlled.
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Alloy N09935, on the other hand, has been specifically developed with enhanced fabricability and machinability. It does not harden as rapidly as 718 and tends to form more manageable chips.
According to industry machining trials, Alloy N09935 typically shows 20–30% better machinability than Alloy 718 under similar cutting conditions.
3.2 Tool Life
Due to its lower work-hardening rate, tool life when machining Alloy N09935 is generally longer. Cutting tools, especially carbide inserts, maintain their sharpness and resist flank wear for extended periods.
By contrast, Alloy 718’s abrasive and tough microstructure accelerates wear and crater formation on tool surfaces. This results in more frequent tool changes and longer downtime.
| Parameter | Alloy N09935 | Alloy 718 |
|---|---|---|
| Tool Wear Rate | Moderate | High |
| Chip Formation | Segmented / Controlled | Continuous / Tough |
| Cutting Temperature | Lower | Higher |
| Work Hardening | Moderate | Severe |
| Tool Life (relative) | 1.3×–1.5× | 1.0× (reference) |
3.3 Surface Finish
Both alloys can achieve smooth finishes with the right cutting parameters, but Alloy N09935 allows higher feed rates and less risk of surface tearing.
For precision parts like valve bodies, tubing connectors, and pump shafts, this leads to fewer secondary polishing steps and tighter dimensional tolerances.
3.4 Heat Generation and Thermal Conductivity
Alloy 718’s low thermal conductivity traps heat at the tool-chip interface, causing thermal softening and premature wear. Alloy N09935, while still low-conductivity, exhibits slightly better heat dissipation, resulting in cooler cutting conditions and reduced deformation.
4. Recommended Machining Parameters
While specific parameters depend on the equipment and tooling used, typical comparative guidelines are:
| Operation | Alloy N09935 | Alloy 718 |
|---|---|---|
| Turning | 40–60 m/min (carbide) | 25–40 m/min (carbide) |
| Drilling | 8–15 m/min | 6–12 m/min |
| Milling | 30–50 m/min | 20–35 m/min |
| Feed Rate | 0.05–0.15 mm/rev | 0.03–0.1 mm/rev |
| Coolant | Abundant flood cooling | Required flood cooling |
The data clearly show that Alloy N09935 allows slightly higher cutting speeds and better tool economy, leading to improved machining productivity.
5. Machining Recommendations
5.1 Tooling
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Carbide inserts (grade ISO K20–K30) are generally suitable for roughing.
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Coated carbides (TiAlN, AlTiN) improve wear resistance in high-heat conditions.
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For finishing operations, CBN or ceramic inserts may be used on Alloy 718 but are less necessary for N09935.
5.2 Cutting Conditions
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Use sharp tools with positive rake angles to reduce cutting force.
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Maintain consistent feed rates to avoid rubbing and strain hardening.
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Employ copious coolant flow to dissipate heat effectively.
5.3 Chip Control
Alloy 718 tends to produce long, continuous chips, which require chip breakers or peck drilling. Alloy N09935 forms shorter, more manageable chips, which improves safety and stability during high-speed operations.
5.4 Surface Integrity
In both alloys, avoid excessive cutting pressure and high-temperature zones that can cause micro-cracking or white layer formation. For critical components in aerospace or energy systems, post-machining stress relief is often recommended.
6. Case Study: Oilfield Component Machining
A leading oilfield equipment manufacturer reported significant cost savings after switching from Alloy 718 to Alloy N09935 for certain valve stem and mandrel components.
Before (Alloy 718):
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Cutting speed: 35 m/min
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Tool life: 20 minutes
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Tool change frequency: every 8 parts
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Surface roughness: Ra 1.6 µm
After (Alloy N09935):
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Cutting speed: 50 m/min
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Tool life: 40 minutes
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Tool change frequency: every 15 parts
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Surface roughness: Ra 1.2 µm
The result was a productivity increase of over 25% and a 40% reduction in tooling costs, without compromising mechanical or corrosion performance.
7. Mechanical Comparison Impact on Machinability
| Property | Alloy N09935 | Alloy 718 |
|---|---|---|
| Yield Strength (MPa) | 690–930 | 1030–1275 |
| Hardness (HRC) | 25–32 | 35–44 |
| Elongation (%) | 30–40 | 12–20 |
The lower hardness and higher ductility of Alloy N09935 directly contribute to its better machinability. Alloy 718’s extreme hardness and high yield strength, while beneficial for high-temperature performance, increase the cutting resistance significantly.
8. Post-Machining Treatments
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Alloy N09935 typically undergoes solution annealing and aging to reach final properties.
Machining can be done in the annealed condition to optimize tool life. -
Alloy 718 is also often machined in the solution-treated state, but due to its rapid work-hardening, intermediate stress-relief steps may be required for complex geometries.
Both alloys may need final heat treatment after machining to restore mechanical properties.
9. Cost and Production Considerations
Although the raw material cost of Alloy N09935 is similar to or slightly lower than Alloy 718, the total manufacturing cost can be much lower because:
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Less tool consumption
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Shorter machining cycle time
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Reduced rework and polishing
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Improved dimensional control
For companies machining large volumes of components — such as wellhead connectors, downhole tools, and pump housings — these savings can be significant.
10. Choosing Between N09935 and 718
| Criteria | Recommended Alloy |
|---|---|
| Aerospace turbine parts | Alloy 718 |
| Sour-gas oilfield components | Alloy N09935 |
| Highest tensile strength needed | Alloy 718 |
| Balanced machinability and corrosion resistance | Alloy N09935 |
| Complex machining geometry | Alloy N09935 |
| High-temperature bolts | Alloy 718 |
In summary:
If your application involves extreme heat (above 650°C) — choose Alloy 718.
If it involves sour environments, seawater exposure, and cost-sensitive machining — Alloy N09935 is the better option.
11. SASAALLOY Technical Insights
SASAALLOY, a professional supplier of nickel-based alloys, offers comprehensive machining data, technical support, and certified materials for clients worldwide.
Our product line includes Alloy N09935, 718, 925, and 945, all meeting ASTM, ASME, and NACE MR0175 standards.
With years of experience serving the energy, petrochemical, and aerospace industries, we provide:
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Precision-machined bars, tubes, and forgings
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Custom heat treatment and aging
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PMI testing and 3.1/3.2 certification
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Fast global shipment and technical consulting
Whether you need raw stock or finished components, SASAALLOY ensures consistent quality, tight tolerances, and optimized machinability performance.
(Logo SASAALLOY)
12. Conclusion
The machinability of Alloy N09935 is significantly better than Alloy 718, making it an attractive choice for engineers seeking a balance between strength, corrosion resistance, and ease of fabrication.
While Alloy 718 remains indispensable for high-temperature aerospace and turbine applications, Alloy N09935 is emerging as the preferred material for oilfield and chemical process components that demand precision machining, high strength, and excellent sour-gas resistance.
By choosing the right alloy and machining strategy, manufacturers can achieve higher productivity, longer tool life, and lower costs—without sacrificing reliability or performance.
For more information, technical datasheets, or customized machining advice, contact SASAALLOY, your trusted partner in high-performance nickel alloys.
Post time: Oct-29-2025