A ball screw is not made from one material. It is a matched assembly consisting of a screw shaft, ball nut, steel balls, recirculation components, seals and lubricant.
Each component has a different function. The screw and nut raceways must resist repeated rolling-contact stress, the shaft and nut bodies must retain sufficient strength and toughness, and the steel balls must maintain accurate diameter, roundness and surface condition.
For standard DLY ball screws, the commonly specified combination is an S55C screw shaft, a 20CrMo ball nut and working surfaces hardened to approximately HRC 58–62.
What Materials Are Used in a DLY Ball Screw?
| Component | DLY Standard Material | Main Requirement | What Should Be Checked |
|---|---|---|---|
| Screw shaft | S55C | Hardened working surface combined with sufficient shaft strength and toughness | Raceway hardness, straightness, runout, lead accuracy and surface condition |
| Ball nut | 20CrMo | Hard internal raceways, stable geometry and sufficient body toughness | Raceway condition, nut dimensions, circulation, preload and axial clearance |
| Rolling balls | Hardened precision steel balls | High hardness, accurate diameter, roundness and rolling-fatigue resistance | Ball grade, diameter group, surface defects and matching with the raceways |
| Recirculation components | Steel or engineering polymer according to the nut design | Reliable ball guidance, impact resistance and stable circulation | Cracks, looseness, deformation, impact noise and circulation interruption |
| Seals and wipers | Elastomer or engineering polymer | Retain lubricant and reduce contamination entering the nut | Wear, seal contact, chemical compatibility and operating resistance |
A ball screw is a matched assembly. The screw shaft, nut, steel balls, circulation components and seals have different material requirements.
Why DLY Uses S55C for the Screw Shaft
S55C is a medium-carbon steel that provides a practical balance between strength, machinability, heat-treatment response and production cost.
A ball screw shaft must satisfy two requirements that appear to conflict:
- The thread raceway must be hard enough to resist repeated rolling contact, wear and indentation.
- The shaft body must retain enough toughness to resist bending, axial force, torque and handling damage.
Heat treatment allows the working surface to obtain the required hardness while the complete shaft does not need to behave like a uniformly hardened and brittle component.
| S55C Characteristic | Effect on the Ball Screw |
|---|---|
| Responds to surface hardening | Allows the working raceway to obtain higher wear and indentation resistance |
| Retains a tougher core | Helps the shaft resist bending, impact and stress around machined shaft ends |
| Suitable machinability | Supports thread production and customized bearing seats, threads and coupling ends |
| Limited natural corrosion resistance | Requires lubrication, anti-rust protection, suitable storage and environmental sealing |
Why DLY Uses 20CrMo for the Ball Nut
The ball nut contains internal load-carrying raceways, circulation passages, mounting surfaces and relatively thin structural sections. Its material must provide hard working surfaces while retaining sufficient body strength and toughness.
DLY standard ball nuts commonly use 20CrMo alloy steel. The final performance depends not only on the material name but also on the heat-treatment process, raceway hardness, dimensional stability and groove accuracy.
A properly manufactured ball nut should provide:
- Hardened internal working raceways
- A sufficiently strong and tough nut body
- Stable flange and mounting dimensions
- Consistent geometry between loaded circuits
- Reliable ball circulation through the complete nut
The material grade alone cannot confirm the nut's dynamic load rating, static load rating or stiffness. Those values also depend on ball diameter, contact geometry, number of loaded circuits and effective load-carrying length.
What Does HRC 58–62 Mean?
DLY standard SFU ball screws specify a working-surface hardness of approximately HRC 58–62.
This hardness range helps the raceways resist:
- Rolling-contact wear
- Indentation under concentrated contact load
- Loss of groove geometry
- Premature growth of axial clearance
- Surface fatigue under repeated operation
Because the specification refers to surface hardness, it should not be interpreted as meaning that the complete screw cross-section has the same hardness.
| Heat-Treatment Item | If Insufficient | Why Control Is Necessary |
|---|---|---|
| Surface hardness | Raceway wear and indentation may develop earlier | Excessive hardness or poor treatment can increase brittleness or distortion |
| Effective hardened layer | Softer supporting material may deform below the contact surface | The required depth depends on component size, load and heat-treatment design |
| Hardness uniformity | Local soft zones may become early wear points | A single hardness reading cannot confirm the condition of an entire long screw |
| Dimensional stability | Shaft straightness or nut geometry may change | Heat treatment must be followed by appropriate finishing and inspection |
Steel-Ball Quality Is Part of the Material System
The load is transferred through the steel balls between the screw and nut raceways. Their size and surface condition directly influence load distribution, running torque, noise, stiffness and preload.
The balls should provide:
- Accurate diameter and roundness
- High and consistent hardness
- Low surface roughness
- No visible pits, scratches or cracks
- Correct diameter grouping for the required clearance or preload
DLY's publicly listed standard specification does not identify one universal steel-ball grade for every ball screw series. Critical projects should confirm the ball specification and acceptance requirements before ordering.
Material Does Not Determine Ball Screw Accuracy
Material and lead accuracy describe different product characteristics.
Two ball screws may both use S55C shafts and 20CrMo nuts but have different accuracy, backlash, stiffness and running performance because their manufacturing and matching processes are different.
| Parameter | What It Mainly Affects | What It Does Not Prove |
|---|---|---|
| Shaft and nut material | Strength, toughness, hardenability and manufacturing response | C3, C5, C7 or C10 lead accuracy |
| Surface hardness | Resistance to wear and contact indentation | Lead error, straightness or preload |
| Rolled or ground process | Thread geometry, lead accuracy, finish, cost and delivery time | Load rating without considering ball and nut geometry |
| Ball and groove geometry | Contact pattern, load distribution, stiffness and rated load | Corrosion resistance or shaft straightness |
| Preload | Axial clearance, reversal behavior, stiffness and running torque | Higher material hardness or automatically higher Coa |
Rolled and Ground Ball Screws May Use Similar Materials
Rolled and ground ball screws are primarily distinguished by their thread-manufacturing and finishing processes, not by a simple division between low-quality and high-quality steel.
| Comparison | Rolled Ball Screw | Ground Ball Screw |
|---|---|---|
| Thread production | The groove is formed through controlled material deformation | The groove is finished using precision grinding |
| Common DLY accuracy direction | C7 and C10 for general automation and CNC applications | C5 and selected higher-accuracy requirements |
| Production characteristics | Efficient production, shorter lead time and lower cost | Tighter process and inspection control with higher manufacturing cost |
| Can material alone identify the type? | No | No |
The same basic material combination can therefore be used in products with different accuracy grades. The difference lies in thread production, heat-treatment control, finishing, measurement and assembly matching.
Are 52100, GCr15 or SUJ2 Better for the Shaft?
High-carbon chromium bearing steels such as 52100, GCr15 and SUJ2 are commonly associated with bearing rings, rolling elements and selected precision motion components.
Their high hardness and rolling-contact properties do not mean that they are automatically the best shaft material for every ball screw.
The shaft-material decision must also consider:
- Rolled or ground production method
- Screw diameter and total length
- Straightness after heat treatment
- Shaft-end machining requirements
- Required load, speed and service life
- Manufacturing cost and material availability
For standard DLY SFU products, the published shaft material is S55C. A different steel grade should be treated as a separate customized specification rather than assumed from another manufacturer's catalog.
Can 304 or 316 Stainless Steel Be Used?
Stainless steel can improve corrosion resistance, but corrosion resistance alone does not make a material suitable for a highly loaded ball screw raceway.
Common 304 and 316 stainless steels should not be treated as direct replacements for a hardened S55C screw raceway or 20CrMo nut raceway.
A corrosion-resistant ball screw must be evaluated as a complete system:
- Achievable raceway hardness
- Dynamic and static load ratings
- Steel-ball and nut materials
- Coating or surface-treatment option
- Seal and return-component compatibility
- Lubricant compatibility
- Water, salt, coolant or cleaning-chemical exposure
Why Titanium and Brass Are Not Standard Choices
Titanium Screw Shafts
Titanium has a useful strength-to-weight ratio, but a ball screw raceway also requires high contact hardness, wear resistance, stable heat treatment and accurate thread processing.
Specialized lightweight mechanisms may use unusual materials or coatings, but titanium should not be presented as a routine alternative to DLY's standard S55C shaft.
Brass Ball Nuts
Brass and bronze are commonly associated with sliding lead-screw nuts. In those systems, the screw thread slides directly against the nut material.
A recirculating ball nut works differently. Its load is transferred through hardened balls between hardened screw and nut raceways. DLY standard SFS, SFU, DFU and related ball nuts therefore use hardened steel structures rather than brass raceways.
| Nut Type | Contact Method | Typical Material Direction |
|---|---|---|
| Sliding lead-screw nut | Direct sliding contact between the screw and nut threads | Bronze, brass, engineering polymer or other sliding material |
| Recirculating ball nut | Rolling contact through balls between screw and nut raceways | Heat-treated steel nut body with hardened working raceways |
How Material Affects Ball Screw Performance
| Performance Item | Material-Related Influence | Other Important Factors |
|---|---|---|
| Wear resistance | Steel composition and raceway hardness affect resistance to surface wear | Lubrication, contamination, preload and surface finish |
| Load capacity | Material and heat treatment must support repeated contact stress | Ball diameter, groove geometry, contact angle and loaded circuits |
| Fatigue life | Material cleanliness and heat treatment influence rolling-fatigue resistance | Actual axial load, shock, alignment and lubrication |
| Lead accuracy | Dimensional stability supports accurate manufacturing | Rolling or grinding process, measurement and compensation |
| Corrosion resistance | Standard S55C and 20CrMo require environmental protection | Coating, lubricant, covers, seals, storage and maintenance |
| Shaft straightness | Material and heat-treatment response affect distortion | Manufacturing control, handling, storage and transport |
How to Verify Ball Screw Material Quality
A polished appearance cannot confirm the steel grade, heat treatment or hardened-raceway condition. Material quality should be verified together with finished-product performance.
1. Confirm the Written Specification
The quotation or technical drawing should state:
- Screw-shaft material
- Ball-nut material
- Working-surface hardness range
- Rolled or ground production method
- Accuracy grade
- Preload or axial-clearance requirement
- Special coating or corrosion-protection requirement
2. Review Material Documentation
For critical orders, request the agreed material and inspection documentation before production. A raw-material certificate helps identify the steel grade, but it does not confirm the quality of the finished raceway.
3. Check Raceway Hardness
Hardness must be measured using a suitable method and test position. Measuring an unhardened machined shaft end does not confirm the hardness of the load-carrying thread raceway.
4. Inspect Straightness and Runout
Heat treatment, machining, storage and transport can affect shaft straightness. A screw can use the correct steel and hardness but still produce vibration and uneven running torque if it is bent.
5. Test the Nut Through the Usable Stroke
Rotate or move the nut through the usable screw length and look for:
- Local tight spots
- Sudden loose sections
- Clicking or grinding noise
- Uneven rotational torque
- Return-system interference
- Visible rust or raceway damage
See How to Check the Quality of a Ball Screw Nut for additional inspection methods.
Material Selection for Different Applications
| Application | Material Direction | Additional Checks |
|---|---|---|
| General CNC and automation | Standard S55C shaft and 20CrMo nut are normally suitable | Diameter, lead, accuracy, load, speed, lubrication and support arrangement |
| High positioning accuracy | Material may remain similar; manufacturing and inspection become more important | C3 or C5 accuracy, lead error, runout, preload and temperature |
| Heavy axial load | Select a larger or higher-capacity structure before changing steel grade | Ca, Coa, stiffness, buckling, support bearings and required life |
| Wet or corrosive environment | Standard steel requires protection; special materials or coatings require confirmation | Liquid type, concentration, temperature, cleaning and lubricant compatibility |
| High-temperature equipment | Material suitability must be reviewed with the complete nut and lubrication system | Lubricant, seals, thermal expansion, preload and hardness stability |
| Food, medical or cleanroom equipment | Standard materials should not automatically be treated as compliant | Lubricant approval, particle generation, cleaning method and regulatory requirements |
Common Misunderstandings
| Misunderstanding | Correct Explanation |
|---|---|
| A shiny screw must be stainless steel | Hardened carbon steel can also have a polished surface. Confirm the written material specification. |
| The hardest steel always provides the longest life | Hardness must be combined with suitable depth, toughness, geometry, lubrication and cleanliness. |
| Stainless steel is automatically better than S55C | Stainless steel may improve corrosion resistance but can involve different hardness, load, cost and availability. |
| A ground screw must use a different steel | Rolled and ground screws may use similar materials. Their production and accuracy controls differ. |
| Higher hardness means higher positioning accuracy | Hardness affects contact durability. Lead accuracy depends on thread processing and inspection. |
| Brass is a standard ball-nut material | Brass is more typical of sliding lead-screw nuts. Recirculating ball nuts use hardened raceways. |
| Correct material proves the published load rating | Load ratings also depend on groove geometry, ball diameter, contact angle and number of circuits. |
Information to Include in a Material Inquiry
Provide the following information when requesting a standard or special-material ball screw:
- Ball screw series or existing model
- Nominal diameter and lead
- Overall length and effective stroke
- Rolled or ground requirement
- Accuracy grade
- Maximum axial load
- Speed and acceleration
- Required preload or allowable axial clearance
- Screw support arrangement
- Operating temperature
- Dust, coolant, water or chemical exposure
- Required certificates or hardness records
- Special coating or corrosion-protection requirement
- Shaft-end machining drawing and order quantity
View the DLY SFU ball screw specifications for standard shaft material, nut material, hardness, dimensions and available accuracy options.
Frequently Asked Questions
What material does DLY use for standard ball screw shafts?
DLY standard SFU ball screw shafts commonly use S55C. Special projects should confirm the material separately in the quotation or drawing.
What material does DLY use for ball nuts?
DLY standard ball nuts commonly use 20CrMo alloy steel with hardened working raceways.
What is the standard raceway hardness?
DLY standard SFU products specify working-surface hardness of approximately HRC 58–62.
Is S55C stainless steel?
No. S55C is a medium-carbon steel and requires suitable lubrication, anti-rust protection and environmental sealing.
Does a C5 ball screw use better material than a C7 screw?
Not necessarily. C5 and C7 describe lead-accuracy performance. The basic materials may be similar, while the thread production, finishing, inspection and matching processes differ.
Can 304 or 316 stainless steel be specified?
A special corrosion-resistant design may be discussed, but 304 or 316 should not be assumed to provide the same raceway hardness, load rating and life as the standard hardened-steel design.
Does a material certificate prove ball screw quality?
No. It helps identify the raw-material grade, but finished quality also requires hardness, straightness, dimensions, accuracy, preload and running-condition inspection.
Contact DLY
Send DLY your ball screw model, diameter, lead, length, accuracy, load, speed, operating environment and shaft-end drawing. State any material certificate, hardness record, corrosion-protection or special-material requirement before quotation and sample approval.
Email: dlyexport2@dlybearing.com | WhatsApp: +86 16605788856
