Learn what 100Cr6 steel is, how it compares with maraging steel for CNC machining, and how to control hardness, heat treatment, tolerances, tool wear, surface finish, and bearing-grade part quality.
What Is 100Cr6 Steel?
100Cr6 is a high-carbon chromium bearing steel commonly associated with DIN 1.3505, EN 100Cr6, AISI 52100, and JIS SUJ2 equivalents. In CNC machining projects, it is usually selected when the part must resist rolling contact, abrasion, repeated stress, and dimensional change after heat treatment. It is not chosen because it is the easiest steel to machine. It is chosen because its final service condition can deliver high hardness, good wear resistance, and stable performance in precision mechanical assemblies.
Material Identity
The name 100Cr6 gives useful clues about the alloy. The steel contains roughly 1% carbon and about 1.5% chromium, which supports high hardness after quenching and tempering. Compared with ordinary low-carbon steel, 100Cr6 has much higher carbide content and stronger heat-treatment sensitivity. Compared with stainless steel, however, it is not a corrosion-resistant steel; surface protection, lubrication, or controlled working conditions may still be required.
Common Equivalent Names
Engineers and buyers may see the same or similar material under several names depending on the drawing standard, supplier region, or mill certificate. This matters because CNC suppliers often quote based on locally available bar stock, and a mismatch between 100Cr6, 52100, SUJ2, or GCr15 can create confusion during purchasing or inspection.
- DIN / EN: 100Cr6 or 1.3505
- AISI / SAE: 52100 bearing steel
- JIS: SUJ2 bearing steel
- GB: GCr15 bearing steel
- Typical condition for machining: spheroidized annealed or soft annealed bar stock
Is 100Cr6 Commonly Used for CNC Machining?
Yes, 100Cr6 is commonly used for CNC machining, but it is more accurate to say that it is commonly machined as part of a controlled manufacturing route. Many 100Cr6 parts are rough turned, drilled, milled, heat treated, ground, honed, lapped, or hard turned depending on the final tolerance and surface finish. A CNC shop can machine it successfully, but the process plan must respect the material condition. Soft-annealed 100Cr6 behaves very differently from hardened 100Cr6.
Machining Condition
For most custom CNC parts, 100Cr6 is easier to machine before hardening. The spheroidized annealed structure reduces cutting force and improves chip behavior compared with fully hardened stock. After heat treatment, the hardness can become too high for ordinary carbide tooling, so finishing may shift toward grinding, hard turning with CBN tooling, or light finishing passes. This is why drawings should state whether dimensions are required before or after heat treatment.
Typical CNC Workflow
A practical route usually separates material removal, heat treatment, and final accuracy control. The exact route depends on the part shape and tolerance class, but the following pattern is common for bearing-grade components and wear-resistant precision parts.
- Machine from annealed bar to near-net geometry.
- Leave controlled grinding or finishing allowance on critical diameters and raceway-like surfaces.
- Quench and temper according to hardness requirement.
- Finish critical surfaces by grinding, honing, lapping, or hard turning.
- Inspect hardness, roundness, runout, surface roughness, and dimensional stability.
What CNC Machined Parts Are Made from 100Cr6?
100Cr6 is most suitable for parts where the working surface sees repeated contact stress, friction, or sliding wear. It is not usually the first choice for large welded structures, decorative parts, or parts exposed to severe corrosion. The material makes sense when the engineering problem is local surface durability, load-bearing precision, or long service life under rolling or sliding contact.
Bearing and Motion Components
The classic applications are bearing balls, rollers, rings, races, and shafts. In custom CNC machining, the geometry may not look like a standard catalogue bearing part, but the function is often similar: the part needs a hard, smooth, dimensionally accurate surface that can operate with repeated contact. Many buyers choose 100Cr6 when they need a custom bearing-like insert, guide element, positioning feature, or rotating part that must hold size after finishing.
Wear-Resistant Mechanical Parts
Beyond bearings, 100Cr6 may be used for small and medium components exposed to abrasion, pressure, and repeated movement. CNC machining is useful when these parts require holes, threads, shoulders, grooves, flats, or non-standard interfaces that cannot be achieved from standard bearing stock alone.
| Part Type | Why 100Cr6 Is Considered | Typical CNC Concern |
| Bearing rings and race-like parts | High hardness, rolling contact resistance, dimensional stability | Roundness, grinding allowance, heat-treatment distortion |
| Rollers and guide pins | Wear resistance under repeated contact | Concentricity, surface roughness, hardened finishing |
| Bushings and sleeves | Hard sliding surface and load support | Bore accuracy, lubrication groove control |
| Precision shafts | Hard bearing seat and fatigue resistance | Runout, straightness, end-face squareness |
| Wear plates and small inserts | Abrasion resistance in compact areas | Flatness, edge chipping, post-heat-treatment finish |
Why Do Users Choose Maraging Steel for CNC Machined Parts?
Although this article focuses on 100Cr6, many buyers compare it with maraging steel because both can be used for high-strength precision parts. The reason for choosing maraging steel is usually different from the reason for choosing bearing steel. Maraging steel is selected when a part needs very high strength, high toughness, and excellent dimensional stability after aging, while avoiding the high-carbon quench response that can create distortion or cracking risk.
Strength with Low Distortion
Maraging steel is a low-carbon, nickel-rich steel strengthened mainly by aging rather than by high carbon martensite alone. This helps users machine the part in a solution-annealed condition and then age it to high strength with relatively low dimensional movement. For complex CNC components with thin walls, pockets, small details, and tight tolerances, this is a major advantage.
Typical Selection Reasons
In practical RFQ discussions, maraging steel is often considered when the final part cannot tolerate major distortion after heat treatment or when toughness is more important than bearing-style wear behavior. It is also attractive when strength must be achieved without turning the part into a brittle, difficult-to-finish component.
- High strength after aging with relatively low dimensional change.
- Better toughness than many very hard high-carbon steels.
- Good suitability for tight-tolerance aerospace, tooling, and high-load mechanical parts.
- Machining can often be completed before aging, reducing the need for extensive post-hardening grinding.
- Useful for thin-wall or complex CNC parts where stability matters.
Chemical Composition of 100Cr6 and Maraging Steel
Chemical composition explains why these two steels behave so differently in CNC machining and heat treatment. 100Cr6 depends on carbon and chromium to form a hard bearing steel structure. Maraging steel depends on nickel, cobalt, molybdenum, titanium, and aging reactions to achieve high strength. Because of this difference, the same cutting strategy, heat-treatment expectation, or surface finishing route should not be applied blindly to both materials.
100Cr6 Composition
100Cr6 is a relatively simple high-carbon chromium steel. Its composition supports high hardness and wear resistance, but it also means the material can be sensitive to decarburization, overheating, cracking, and grinding burn if the manufacturing route is poorly controlled. The following table gives typical composition ranges used for engineering reference. Actual values should always be confirmed by the material certificate.
| Élément | Typical Range in 100Cr6 | Machining and Performance Meaning |
| Carbone (C) | 0.93-1.05% | Main source of hardness and carbide formation |
| Chrome (Cr) | 1.35-1.60% | Improves hardenability and wear resistance |
| Manganèse (Mn) | 0.25-0.45% | Supports hardenability and steelmaking control |
| Silicium (Si) | 0.15-0.35% | Contributes to strength and deoxidation |
| Phosphore (P) | Max. 0.025% | Controlled impurity for toughness and cleanliness |
| Soufre (S) | Max. 0.015% | Low level supports bearing-grade cleanliness |
| Molybdène (Mo) | Max. 0.10% | May support hardenability in some specifications |
| Copper (Cu) | Max. 0.30% | Residual element controlled by specification |
Maraging Steel Composition
Maraging steel grades vary, but maraging 300 is a common reference grade in CNC discussions. Unlike 100Cr6, it uses very low carbon content and relies on alloy precipitation during aging. This composition is why the material can provide high strength while retaining useful toughness and relatively stable dimensions.
| Élément | Typical Range in Maraging 300 | Machining and Performance Meaning |
| Nickel (Ni) | 18-19% | Base element for maraging behavior and toughness |
| Cobalt (Co) | 8.5-9.5% | Strengthens aging response |
| Molybdène (Mo) | 4.6-5.2% | Supports precipitation hardening |
| Titanium (Ti) | 0.5-0.8% | Forms strengthening precipitates |
| Aluminium (Al) | 0.05-0.15% | Supports aging response |
| Carbone (C) | Max. about 0.03% | Keeps carbon-related brittleness and distortion low |
| Fer (Fe) | Équilibre | Main matrix element |
Physical and Mechanical Properties of 100Cr6
The value of 100Cr6 is not only its chemistry but also the property combination after proper heat treatment. In the annealed condition, it can be machined more economically. In the hardened condition, it can reach a hardness level suitable for demanding wear and contact-stress applications. This condition-dependent behavior is the main reason CNC suppliers ask about final hardness, heat-treatment state, and inspection requirements before quoting.
Propriétés physiques
Typical physical properties help designers estimate part weight, thermal behavior, and process response. 100Cr6 has a density close to many carbon and alloy steels, so weight savings should not be expected compared with ordinary steel. Its thermal conductivity and thermal expansion behavior are important during grinding, hard turning, and press-fit design, especially for precision bearing seats and sleeves.
| Propriété | Valeur typique | Signification de la conception |
| Densité | About 7.80 g/cm3 | Similar weight to many steels |
| Module d’élasticité | About 210 GPa | High stiffness for precision assemblies |
| Thermal expansion | About 11-12 x 10^-6 /K | Important for press fits and heat treatment |
| Conductivité thermique | Moderate for alloy steel | Heat control matters during cutting and grinding |
| Magnétisme | Ferromagnetic | May matter for sensors, handling, or debris attraction |
Mechanical Properties
Mechanical properties depend strongly on heat treatment. In the annealed condition, hardness is much lower and machining is more practical. After quenching and tempering, 100Cr6 can reach high hardness, but the part may require precision finishing to correct size change and achieve the required surface quality.
| État | Typical Property Range | CNC Machining Meaning |
| Spheroidized annealed | Often up to about 207 HB | Preferred for rough machining and drilling |
| Cold worked annealed | May be higher hardness than annealed | Tool load and chip control increase |
| Hardened and tempered | Often around 58-64 HRC depending on route | Requires grinding, CBN hard turning, or very light finishing |
| Final precision condition | High hardness with controlled surface finish | Inspection must include geometry, hardness, and surface integrity |
100Cr6 vs Maraging Steel CNC Machinability
100Cr6 and maraging steel can both be CNC machined, but their machining logic is different. 100Cr6 is usually easier before hardening and much harder to finish after quenching. Maraging steel is often machined in the solution-annealed condition and then aged with less distortion than many quench-hardened steels. This difference affects quotation, tolerance planning, tooling, lead time, and final inspection.
Machinability Before Heat Treatment
Before heat treatment, soft-annealed 100Cr6 can be turned, milled, drilled, and threaded with carbide tooling, but its high carbon and carbide structure still require stable cutting and good chip evacuation. Maraging steel in solution-annealed condition is generally attractive for high-precision machining because the part can often be finished close to final size before aging.
Machinability After Heat Treatment
After hardening, 100Cr6 becomes a wear-resistant steel, which is excellent in service but demanding during finishing. Maraging steel also becomes stronger after aging, but its dimensional stability after aging is one of its main advantages. This is why many complex CNC parts favor maraging steel when strength and geometry stability are more important than bearing-race wear behavior.
| Comparison Point | 100Cr6 Bearing Steel | Maraging Steel |
| Main reason to choose | Wear resistance and rolling contact performance | High strength, toughness, low aging distortion |
| Best machining condition | Spheroidized annealed before hardening | Solution annealed before aging |
| Post-treatment challenge | Quench distortion, high hardness, grinding need | Higher material cost, aging control, alloy cost |
| Final finishing | Grinding, honing, lapping, hard turning | Often less corrective finishing than quenched high-carbon steel |
| Meilleur ajustement | Bearing-like wear parts and hard contact surfaces | Complex high-strength precision parts and thin-wall components |
What Do Users Discuss Most About 100Cr6 CNC Machining?
In real project discussions, users rarely ask only for a dictionary definition of 100Cr6. They ask whether it can be machined, whether it will warp after heat treatment, whether a tolerance can be held after hardening, and whether the part needs grinding instead of only CNC milling or turning. These questions are practical because 100Cr6 is often used in precision assemblies where a small mistake in heat treatment, allowance, or surface finish can cause performance problems.
Hardness and Heat Treatment
The most common concern is final hardness. A buyer may request 60 HRC or higher, but the drawing may also include tight dimensions, sharp transitions, small holes, or thin walls. If the heat-treatment plan is not considered early, the part may move, crack, or require expensive correction. A better drawing defines final hardness range, final machining sequence, and inspection after heat treatment.
Tolérance et qualité de surface
Another frequent concern is whether CNC machining alone can deliver the required bearing-grade surface. For many 100Cr6 parts, a milled or turned surface is not enough for the most critical contact areas. Surface roughness, roundness, cylindricity, and runout may require grinding or lapping, not just a sharper tool or slower feed.
- Can 100Cr6 be machined after hardening?
- Should the part be rough machined before heat treatment?
- How much grinding allowance should be left?
- Will small holes or grooves deform after quenching?
- Is 100Cr6 corrosion resistant enough without coating?
- Can threads be cut before hardening or should they be finished later?
CNC Machining Challenges of 100Cr6
The machining difficulty of 100Cr6 comes from the same properties that make it useful: high carbon content, carbide structure, hardenability, and high final hardness. A part may seem simple in CAD, but the manufacturing route can become complex when the drawing requires hard contact surfaces, close tolerances, thin sections, or excellent surface finish. For this reason, the challenge is not only cutting the material; it is controlling the complete process from raw stock to final inspection.
Tool Wear and Cutting Heat
Even in the annealed state, 100Cr6 can be more abrasive than low-carbon steel. Tool wear may increase if cutting speed is too aggressive or if coolant does not reach the cutting zone. When tool wear is not controlled, the result can be poor surface finish, size drift, burr formation, or work hardening at the surface. Stable fixturing and predictable tool life are important for repeat orders.
Distortion and Surface Integrity
Heat treatment can change dimensions, especially in rings, sleeves, thin sections, and parts with uneven wall thickness. Grinding can also damage the surface if heat is not controlled. For bearing-grade parts, surface integrity is not cosmetic; grinding burn, decarburization, microcracks, or residual tensile stress can reduce service life.
- High tool wear when machining harder or poorly annealed stock.
- Risk of distortion after quenching, especially in asymmetric parts.
- Need for finishing allowance on critical surfaces.
- Difficulty holding tight holes and bores after heat treatment.
- Risk of grinding burn during final finishing.
- Potential edge chipping on very hard, sharp features.
How to Solve 100Cr6 CNC Machining Difficulties
The best way to machine 100Cr6 is to decide the manufacturing route before cutting begins. A supplier should not treat 100Cr6 like ordinary steel if the part must be hardened, ground, or inspected for precision contact surfaces. Early planning reduces rework, scrap, and quote surprises. The most effective measures combine material condition control, tooling strategy, heat-treatment allowance, and final inspection.
Process Planning Measures
For most 100Cr6 CNC parts, the safest approach is to machine the part in the soft condition, leave the correct allowance, then finish critical features after heat treatment. The allowance cannot be random. Too little allowance leaves distortion uncorrected; too much increases grinding time, heat input, and cost. For thin or ring-shaped parts, symmetric machining and stress control can also reduce movement.
Tooling and Inspection Measures
Cutting tools should match the material state. Carbide tools are suitable for annealed machining, while CBN tools may be needed for hard turning. Coolant, tool path stability, and tool life monitoring are important because size drift may not be obvious until inspection. Final quality control should check not only length and diameter but also hardness, roughness, runout, flatness, roundness, and surface damage.
| Difficulté | Recommended Measure | Expected Result |
| Usure des outils | Use coated carbide, stable cutting parameters, and tool-life monitoring | More consistent size and surface finish |
| Déformation due au traitement thermique | Machine symmetrically and leave controlled finishing allowance | Higher chance of meeting final tolerance |
| Hard finishing | Use grinding, honing, lapping, or CBN hard turning | Better surface quality on hardened areas |
| Poor bore accuracy | Finish bore after heat treatment when needed | Improved roundness and fit |
| Grinding burn | Use correct wheel, coolant, feed, and burn inspection | Better surface integrity |
| Unclear requirements | Define final hardness, tolerance state, and inspection method | Fewer quotation and production disputes |
Conclusion
100Cr6 is a strong choice for CNC machined bearing-like parts, wear-resistant inserts, rollers, sleeves, shafts, and precision contact components. Its value comes from high hardness and wear resistance after heat treatment, but its machining route must be planned carefully. Compared with maraging steel, 100Cr6 is better for hard contact and wear applications, while maraging steel is usually better for complex high-strength parts that need low distortion after aging. The right choice depends on final function, tolerance, hardness, finishing method, and cost.
FAQ
Can 100Cr6 be CNC machined?
Yes. 100Cr6 can be CNC turned, milled, drilled, and threaded, especially in the spheroidized annealed condition. For hardened 100Cr6, ordinary machining becomes difficult, so grinding, lapping, honing, or CBN hard turning may be required for precision surfaces.
Is 100Cr6 the same as 52100 steel?
100Cr6 is often treated as the European equivalent of AISI 52100 bearing steel. They are very similar high-carbon chromium bearing steels, but the exact specification, supply condition, and certificate values should be checked before production.
Is 100Cr6 corrosion resistant?
No. 100Cr6 is not a stainless steel. It has chromium for hardenability and wear resistance, not for stainless corrosion behavior. Lubrication, coating, oiling, or environmental control may be needed when corrosion risk exists.
When should maraging steel be chosen instead?
Maraging steel is often better when the part needs very high strength, good toughness, complex geometry, and low dimensional change after aging. It is not usually chosen as a direct replacement for 100Cr6 when bearing-style wear resistance is the main requirement.