Nickel and Nickel Alloys for Machining: Corrosion, Heat, Work Hardening and Tooling

Nickel machining starts with the exact material callout, not the word nickel. Nickel 200, Nickel 201, Alloy 625 and Alloy 718 differ in chemistry, strengthening route, condition and mechanical response. ASTM B160-24 covers Nickel 200 and Nickel 201 rod and bar, ASTM B446-26 covers UNS N06625 rod and bar, and ASTM B637-25 covers precipitation-hardenable nickel alloy rod, bar, forgings and forging stock including UNS N07718. For CNC work, grade and condition come before tooling. Geometry, feature type, tool reach, coolant access, setup rigidity, surface finish and inspection method then determine the process window.

1. What Is Nickel, and Which Properties Matter in Manufacturing?

Nickel is a metallic element, Ni, atomic number 28. For readers asking what is nickel made of, elemental nickel is Ni; engineering alloys then add chromium, molybdenum, iron, copper or other elements. Engineers use nickel metal both as a commercially pure material and as the base of nickel alloys selected for corrosion resistance, high-temperature strength or a combination of the two. The International Nickel Study Group lists nickel density at about 8.9 g/cm³ and the nickel melting point at about 1453°C. Pure nickel is ferromagnetic below its Curie region. Those basic nickel properties matter, but a CNC drawing still needs a grade, product form and condition. The properties of nickel that drive manufacturing decisions include nickel mechanical properties, nickel thermal properties, corrosion response and magnetic behavior.

Nickel 200 provides a useful reference for commercially pure nickel. Special Metals publishes a density of 8.89 g/cm³, a melting range of 1435 to 1446°C and nickel thermal conductivity of 70.3 W/m·°C at 20°C for annealed Nickel 200. The higher thermal conductivity of commercially pure nickel is one reason it is inaccurate to describe every nickel alloy as a low-conductivity material. Nickel hardness, nickel tensile strength, nickel yield strength and nickel ductility also change with condition, so published typical values must not be mixed with ASTM minimum acceptance values.

A material definition such as “nickel material” or “nickel bar” is still incomplete for purchasing. The drawing or RFQ should identify the UNS designation, applicable specification, product form and condition. EPOC CRAFTER’s CNC machining materials selection guide explains how material condition, machinability, inspection and part geometry affect CNC process choice.

2. Nickel Metal and Nickel Alloys Are Different Engineering Families

The types of nickel alloys discussed here include commercially pure nickel, solid-solution corrosion-resistant grades and precipitation-hardenable systems. The phrases nickel alloy, nickel alloys, nickel based alloys, nickel base alloys, high nickel alloys, nickel superalloys and nickel based superalloys cover several metallurgical systems. They do not describe one nickel composition, one hardness range or one nickel machinability level.

Material family	Example	Strengthening route	Main decision driver	Specification
Commercially pure nickel	Nickel 200, UNS N02200	Composition and cold work	Purity, corrosion resistance, thermal or electrical function	ASTM B160-24
Low-carbon commercially pure nickel	Nickel 201, UNS N02201	Composition and cold work	Lower carbon limit for specified service contexts	ASTM B160-24
Corrosion-resistant nickel alloy	Alloy 625, UNS N06625	Ni-Cr-Mo-Nb chemistry, plus condition and cold work where specified	Corrosion resistance with useful strength	ASTM B446-26
Precipitation-hardenable nickel alloy	Alloy 718, UNS N07718	Solution treatment and precipitation hardening	High specified strength and elevated-temperature service	ASTM B637-25

This split answers a practical grade question. Nickel grades and nickel alloy grades must be tied to a material system before machining data are compared. A change in condition can also change strength and cutting behavior, so heat treatment before or after CNC machining belongs in process planning when the final condition is heat treated.

3. Commercially Pure Nickel: Nickel 200 vs Nickel 201

ASTM B160-24 identifies Nickel 200 as UNS N02200 and low-carbon Nickel 201 as UNS N02201. Both are covered as hot-worked and cold-worked rod and bar. The strongest purchasing distinction in the standard chemistry table is carbon.

Element	Nickel 200, N02200	Nickel 201, N02201	Engineering meaning
Nickel, min	99.0%	99.0%	Both are commercially pure nickel
Copper, max	0.25%	0.25%	Same limit
Iron, max	0.40%	0.40%	Same limit
Manganese, max	0.35%	0.35%	Same limit
Carbon, max	0.15%	0.02%	Nickel 201 is the low-carbon grade
Silicon, max	0.35%	0.35%	Same limit
Sulfur, max	0.01%	0.01%	Same limit

The Nickel 200 alloy callout cannot be represented by one ASTM strength value. Nickel 200 properties change with condition, shape and size. For annealed rod and bar, B160-24 specifies minimums of 380 MPa tensile strength, 105 MPa 0.2% yield strength and 40% elongation. Cold-worked rounds have higher minimum strength requirements that vary by diameter. That is why Nickel 200 machinability and process qualification should be tied to the incoming condition.

The Nickel 201 alloy callout needs the same treatment. Nickel 201 properties must be read with its condition and product form. B160-24 Appendix X1 states that N02201 is intended for fused caustic and other fused salts and for temperatures above 600°F (316°C), but that appendix is nonmandatory. It does not establish a universal service limit, corrosion rate, creep life or statement that Nickel 201 is preferred above 316°C in every application.

For Nickel 200 vs Nickel 201, specify the required UNS first, then confirm specification year, product form, dimensions, condition and certification. B160-24 made certification mandatory in the 2024 edition. Its rod and bar tolerances are incoming stock requirements, not finished CNC tolerances. Finished features still follow the drawing and inspection plan.

4. Alloy 625 and Alloy 718: Grade and Condition Change the Decision

Nickel alloy 625, UNS N06625, and nickel alloy 718, UNS N07718, are both high nickel alloys, but their property systems are different.

ASTM B446-26 defines N06625 as a nickel-chromium-molybdenum-niobium alloy and separates three grades or conditions. Grade 1 is annealed, Grade 2 is solution annealed, and Grade 3 is solution annealed and cold worked. Inconel 625 properties cannot be reduced to one strength value. N06625 chemistry includes nickel 58.0% minimum, chromium 20.0 to 23.0%, molybdenum 8.0 to 10.0% and niobium 3.15 to 4.15%. The standard chemistry establishes material identity. It does not establish corrosion life or Inconel 625 machining parameters.

N06625 condition	Size basis	UTS min	0.2% YS min	Elongation min	Decision meaning
Grade 1, annealed	≤102 mm	827 MPa	414 MPa	30%	Higher room-temperature minimums than Grade 2
Grade 1, annealed	>102 to 254 mm	758 MPa	345 MPa	25%	Size changes the ASTM minimums
Grade 2, solution annealed	All sizes	690 MPa	276 MPa	30%	Use when the specified solution-annealed condition is required
Grade 3, solution annealed and cold worked	≤63 mm	930 MPa	690 MPa	25%	Cold work is part of the specified condition

Alloy 718 properties are condition-specific. ASTM B637-25 covers precipitation-hardenable nickel alloys for moderate or high-temperature service, including UNS N07718. In a specified solution-treated and precipitation-hardened N07718 condition, Table 3 includes minimum values around 1240 MPa tensile strength, 1035 MPa yield strength, 12% elongation and 15% reduction of area. Those values apply to the stated condition. They are not universal Inconel 718 properties. For high temperature nickel alloys, B637-25 also includes stress-rupture acceptance requirements for specified alloy and heat-treatment combinations. A stress-rupture coupon result is not a finished-part life prediction.

For Alloy 625 vs Alloy 718, start with corrosion environment, temperature, sustained stress, required strength, product form and final heat-treatment state. Alloy 625 is often selected when nickel alloy corrosion resistance is a main driver. Alloy 718 is selected when a precipitation-hardened strength level is required. Neither choice can be reduced to “corrosion grade” versus “heat grade.”

5. Why Nickel and Nickel Alloys Are Difficult to Machine

Machining nickel alloys often exposes nickel work hardening first at the cutting edge. Nickel Institute machining guidance recommends sharp tools, positive rake, adequate clearance, enough chip load to avoid rubbing, rigid setups and cuts that penetrate below the previously work-hardened surface. Dwell and light rubbing can leave a harder layer for the next pass.

That mechanism is separate from a specified cold-worked material condition. ASTM B446 Grade 3 proves that cold work can be part of an N06625 supply condition, but B446 does not provide a machining-induced work-hardening rate, hardened-layer depth, cutting speed, feed, carbide grade or tool-life requirement.

Cutting heat is alloy-specific. Commercially pure Nickel 200 conducts heat much better than many nickel superalloys, while high-strength nickel alloy machining can concentrate heat at the tool-chip interface. Tool wear, adhesion, chip evacuation and insufficient rigidity can make the temperature problem worse. Nickel cutting tools therefore need to be selected with the exact material condition and operation in mind.

5.1 EPOC CRAFTER Engineering Note: Solution-Annealed Alloy 625 Bore

EPOC CRAFTER shop-floor data provides one bounded example. A 48-piece high-pressure instrumentation gland body was machined from solution-annealed Alloy 625, UNS N06625, ASTM B446-26 round bar. The part required an Ø18 H7 through bore at 18.000 to 18.018 mm, sealing-face runout ≤0.020 mm TIR and bore finish ≤Ra 1.6 µm.

During first-off machining, the bore showed taper, intermittent tearing and rapid boring-insert wear. A 55 mm boring-bar overhang produced light chatter and 0.012 to 0.018 mm taper. Repeated spring passes increased heat and dimensional drift. Three parts needed bore rework and one part exceeded the upper bore limit.

The corrected route reduced boring-bar overhang from 55 to 38 mm, removed spring passes, left 0.15 mm radial stock for finishing, used a 0.08 mm/rev finish feed and applied 70 bar through-tool coolant in one continuous finish pass. Production bores then measured 18.006 to 18.015 mm, bore taper stayed at or below 0.006 mm and measured bore roughness was Ra 1.12 µm. Finish-bore insert life increased from 8 to 21 parts per edge under the same wear-change limit. No additional rework or scrap occurred on the remaining 44 parts. Cycle time moved from 18.6 to 17.2 min/part.

The result belongs to this solution-annealed N06625 bore, machine and tooling package. It does not qualify Inconel 718 machining, materially deeper bores, interrupted cuts or a lower-rigidity setup.

6. Turning, Milling and Drilling Nickel Alloys

A useful nickel machining process sheet starts from the feature. Turning needs stable engagement and enough stock for a true cut. Milling adds repeated entry and exit, so edge loading and engagement need control. Nickel drilling needs chip space, coolant access and a feed that forms a chip without prolonged rubbing.

Operation	Tool	Cutting speed	Feed	DOC / WOC	Result context
OD rough turning	PVD carbide CNMG 120408	38 m/min	0.20 mm/rev	DOC 2.0 mm radial	Continuous cut, flood coolant
OD finish turning	PVD carbide DNMG 150604	45 m/min	0.08 mm/rev	DOC 0.30 mm radial	Fresh edge, one finish pass
Pilot nickel drilling, Ø12	Solid-carbide TiAlN drill	24 m/min	0.10 mm/rev	Full diameter	70 bar through-tool coolant
Drilling, Ø17.4	Solid-carbide TiAlN drill	22 m/min	0.11 mm/rev	Full diameter	No dwell at breakthrough
Finish boring, Ø18 H7	Positive carbide boring insert	32 m/min	0.08 mm/rev	DOC 0.15 mm radial	38 mm overhang, continuous pass
Wrench-flat milling	Ø12 solid-carbide 4-flute end mill	30 m/min	0.035 mm/tooth	WOC 3.0 mm, DOC 8.0 mm	Climb milling, constant engagement
M42 × 1.5 thread	Carbide laydown full-profile insert	18 m/min	1.50 mm/rev	Multi-pass	Fresh insert, no dwell at runout

The drilling operation is a useful warning against reducing feed by reflex. The first three parts produced long stringers and slight exit tearing. After feed and coolant delivery were corrected, the chips became shorter helices and the exit tearing disappeared. Nickel cutting is easier to control when chip form, tool condition and bore surface are inspected together.

A drawing with tight bores, threads, sealing faces or datum-controlled features should also define the inspection state. EPOC CRAFTER’s tight tolerance machining for critical nickel features shows how to place tight control on features that can cause fit, sealing or alignment failure.

7. Corrosion, Heat and Material Selection

Is nickel corrosion resistant? Yes, but nickel corrosion resistance comes from the specific alloy and environment, not nickel content alone. Nickel corrosion and nickel chemical resistance change with pH, chloride level, oxidizing or reducing chemistry, temperature, flow, crevice geometry and sustained stress.

Alloy 625 uses chromium, molybdenum and niobium in a nickel base and is widely selected for aggressive corrosion service. Alloy 718 also resists many environments, but its design identity centers on precipitation-hardened strength. The two materials should not be ranked with a single corrosion or temperature score. Nickel heat resistance also needs the correct data type. Room-temperature ASTM tensile minimums are material acceptance values, not high-temperature design allowables. ASTM B637 stress-rupture requirements qualify specified material conditions under stated test temperature and stress; they do not predict finished-part life.

Nickel vs stainless steel, and more specifically nickel alloy vs stainless steel, is a service decision. Stainless steel can remain the lower-cost option when its corrosion and temperature limits meet the design. A nickel alloy deserves review when pitting, crevice corrosion, reducing-acid exposure, stress-corrosion risk or elevated-temperature strength exceeds the stainless grade’s qualified range. EPOC CRAFTER’s 316 vs 316L stainless steel material specification guide shows the same discipline: chemistry, condition and service exposure decide the grade, not a broad “better alloy” label.

Nickel vs copper is a different comparison. Copper is selected for electrical and thermal conductivity, while nickel metal brings different corrosion, strength and magnetic behavior. The service requirement should decide the material before CNC cost is compared.

8. Raw Material, Specifications, MTR Review and RFQ

Nickel stock can arrive as nickel rod, nickel round bar, nickel alloy bar, nickel alloy rod, nickel plate, nickel alloy plate or other stock forms. The nickel specification must match the form. B160-24 and B446-26 used in this article are rod and bar standards. B637-25 covers rod, bar, forgings and forging stock. Their dimensional tables are raw-stock acceptance criteria, not finished-part tolerances.

Specification	Material focus	Product form	Main control	Not a source for
ASTM B160-24	N02200, N02201	Rod and bar	Chemistry, condition-linked mechanical minimums, dimensions, mandatory certification	Cutting data or finished-part tolerance
ASTM B446-26	N06625	Rod and bar	Grade/condition, chemistry, mechanical minimums, stock dimensions	Inconel 625 machining speed, work-hardening depth or tool life
ASTM B637-25	N07718 and other precipitation-hardenable alloys	Rod, bar, forgings, forging stock	Heat treatment, tensile/hardness requirements, applicable stress rupture	Inconel 718 machining parameters or component life

Before machining, the nickel material certificate should match the drawing or PO for UNS, specification, revision year, product form, heat number, size and condition. Chemistry and mechanical results should be checked against the applicable standard. EPOC CRAFTER’s yield strength vs tensile strength for CNC material selection explains why a certificate tensile value and a design allowable answer different questions.

The Alloy 625 case MTR recorded UNS N06625, ASTM B446-26 and solution-annealed condition. Reported chemistry included Ni 61.22%, Cr 21.48%, Mo 8.72% and Nb+Ta 3.58%, with tensile strength 928 MPa, 0.2% yield strength 512 MPa and elongation 42%. Those results verified the incoming heat. CMM, bore gauge, profilometer and thread-gauge inspection verified the finished part.

A nickel alloy RFQ should state the following before the shop selects stock or nickel machining tools:

• Material: UNS, commercial name, specification, product form and incoming condition.
• Drawing: revision, critical dimensions, GD&T, threads, fits, sealing faces and surface finish.
• Thermal route: post-machining heat treatment and final acceptance condition.
• Verification: nickel material certificate, heat traceability and required mechanical or hardness results.
• Inspection: first article, CMM, bore, runout, surface roughness, thread and any specified NDT.
• Quantity and post-processing: lot size, cleaning, coating or surface treatment, masking and final inspection state.

For geometry review before quotation, EPOC CRAFTER’s CNC DFM design guidelines for nickel machined features connect tool access, feature depth, wall stiffness and tolerance callouts to the manufacturing route.

For finished-part acceptance, the CNC tolerance and inspection standards for machined parts separate drawing tolerances, GD&T and inspection methods from raw-stock specification limits.

9. Applications and Procurement Decisions

For readers asking what is nickel used for, the main nickel uses in engineered parts include corrosion-resistant, high-temperature, electrical and magnetic service. Nickel applications that justify higher material and machining cost usually combine corrosion, heat or strength with a failure consequence. Common nickel alloy applications include chemical-processing valves and fittings, aerospace and turbine hardware, oil and gas instrumentation, high-pressure glands, marine hardware and selected power-generation components.

Do not expand an application list into a material approval. The service medium, stress, temperature and code still decide suitability. The same rule applies to nickel alloy machining services: capability should be judged on the specified alloy, condition, feature set and inspection requirement, not on a generic claim that a shop “machines Inconel.”

For a production RFQ, EPOC CRAFTER’s CNC machining nickel alloy parts capability provides the manufacturing route for milled and turned metal parts, while the material specification and drawing remain the controlling technical documents.

10. FAQ

10.1 Is nickel machinable, and why is nickel hard to machine?

Yes, nickel is machinable, but is nickel easy to machine? That depends on the exact grade and condition. Nickel and high-nickel alloys can work harden under rubbing, generate demanding cutting loads and punish a dull edge. Nickel Institute guidance and the EPOC CRAFTER Alloy 625 case both point to sharp edges, positive chip load, rigid setup and control of dwell as practical variables.

10.2 Does machining nickel require a lot of coolant?

Coolant demand depends on the operation, alloy and tool system. A short facing or cutoff operation can be very different from deep drilling or boring. Directed high-pressure coolant can improve chip evacuation and edge temperature control in confined cuts. The 70 bar value in the EPOC CRAFTER Alloy 625 case belongs to that bore process only.

10.3 What cutting tools work for Inconel 625?

There is no single insert answer without the operation and setup. Carbide is common for many Alloy 625 operations, but grade, geometry, coating, engagement and coolant need to match the cut. Toolmaker data and a qualified shop process are stronger evidence than a generic alloy name.

10.4 Can a thin Inconel 625 part be turned from solid stock?

It can be possible, but stiffness may become the limiting variable. Thin sections can move as stock is removed. Workholding, sequence, support and available tube stock should be reviewed before committing to the route.

10.5 Does nickel rust, and is nickel magnetic?

Pure nickel does not form the same red rust associated with carbon steel, but nickel and nickel alloys can corrode. Elemental nickel is ferromagnetic below its Curie region, while alloying and microstructure can change magnetic response. A magnet test is not enough to verify a nickel UNS designation.