A ball screw is not made from one material alone. The screw shaft, nut, load-carrying balls and recirculation components perform different functions, so each component requires an appropriate combination of steel grade, heat treatment, surface hardness and core toughness.
For most industrial ball screws, material performance depends not only on the steel designation. Raceway hardening, rolling or grinding quality, lubrication, sealing and operating conditions all influence accuracy and service life.
Typical Materials Used in a Ball Screw
The exact material specification varies by manufacturer, production method and product series. The following table shows common engineering choices rather than a universal specification for every ball screw.
| Component | Common Material Types | Typical Treatment | Required Properties |
|---|---|---|---|
| Screw shaft | Medium-carbon steel or chromium-molybdenum alloy steel, such as S55C or SCM-series steel | Induction hardening or carburizing, depending on material and design | Hard raceway surface, wear resistance, fatigue strength and a tough supporting core |
| Ball nut | Case-hardening alloy steel, commonly SCM-series steel | Carburizing and hardening | Wear-resistant internal raceway, dimensional stability and structural strength |
| Steel balls | High-carbon chromium bearing steel, such as SUJ2 or equivalent | Through hardening with precision finishing | High hardness, roundness, surface finish and rolling-contact fatigue resistance |
| Return components | Steel, stainless steel or engineering polymer, depending on the circulation design | Component-specific | Impact resistance, low friction, dimensional consistency and reliable ball circulation |
| Corrosion-resistant versions | Hardenable stainless steel, such as SUS440C, or specially treated steel | Hardening and application-specific surface treatment | Improved corrosion resistance while retaining adequate raceway hardness |
Which Material Properties Matter Most?
1. Raceway Hardness and Wear Resistance
The balls transfer load through small contact areas on the screw and nut raceways. These surfaces therefore experience high repeated contact stress. A hardened raceway resists indentation, pitting and gradual profile wear, helping the ball screw maintain preload and positioning consistency.
Hardness alone is not enough. Surface finish, hardening depth and the uniformity of the heat-treated layer also affect fatigue life. A raceway that is very hard but poorly finished or inadequately supported can still fail prematurely.
2. Core Toughness
The entire shaft should not simply be made as hard and brittle as possible. Surface-hardening processes allow the raceway to carry rolling contact while retaining a tougher core that can better tolerate bending, shock and shaft-end stresses.
3. Rolling-Contact Fatigue Strength
Ball screws operate under repeated cyclic loading. Over time, subsurface fatigue can produce flaking or pitting on the raceway. Clean steel, controlled heat treatment, correct preload and proper lubrication all contribute to fatigue resistance; the material name by itself cannot predict service life.
4. Dimensional Stability
Precision depends on stable raceway geometry and lead accuracy. Controlled heat treatment helps reduce distortion and residual stress during manufacturing. In operation, however, most conventional steels have broadly similar thermal expansion behavior. Temperature rise, shaft length, speed, support arrangement and thermal compensation are therefore more important than assuming that a standard steel ball screw will not expand.
5. Corrosion Resistance
Standard carbon and alloy steels offer strong load-carrying performance but require protection from moisture, condensation, coolant and corrosive contaminants. Lubrication, seals, bellows and suitable surface protection are commonly used.
Hardenable stainless steel or a special coating may be considered for cleanrooms, vacuum equipment, medical equipment or mildly corrosive conditions. Stainless steel does not automatically make a ball screw maintenance-free or suitable for every chemical or marine environment. Load capacity, hardness, lubricant compatibility and the specific corrosive medium must still be evaluated.
Heat Treatment Is as Important as the Steel Grade
In a typical ball screw, the screw and nut raceways are surface hardened because these areas carry the rolling-contact load. Depending on the component and steel grade, manufacturers may use induction hardening, carburizing or through hardening.
- Induction hardening rapidly heats and hardens a controlled surface layer while retaining a tougher core.
- Carburizing increases carbon near the surface before hardening, producing a wear-resistant case over a tougher interior.
- Through hardening is commonly used for bearing balls and some hardenable stainless components where hardness is required through the section.
Important: Published hardness values are usually surface-hardness ranges for a specific component and series. They should not be applied to an entire ball screw without checking the manufacturer's specification.
How to Select a Ball Screw Material
Material selection should start with the application rather than a single preferred steel grade. When requesting a ball screw, provide the following information:
- Required axial load and expected duty cycle
- Speed, acceleration and operating stroke
- Accuracy grade and backlash or preload requirement
- Working temperature and expected temperature variation
- Exposure to moisture, coolant, dust or chemicals
- Lubrication, sealing and maintenance conditions
For ordinary CNC machinery and industrial automation, hardened alloy- or carbon-steel components are widely used because they provide a practical balance of strength, wear resistance and cost. Stainless or specially treated versions should be selected only after the environmental requirements and mechanical trade-offs have been confirmed.
Summary
The key properties of ball screw materials are surface hardness, wear resistance, core toughness, rolling-contact fatigue strength, dimensional stability and appropriate corrosion resistance. These properties are created by the combined choice of steel, heat treatment and precision manufacturing-not by the material name alone.
When comparing ball screws, ask for the material and heat-treatment specification for the actual series being supplied. Accuracy grade, preload, lubrication and environmental protection must also be evaluated because all of them affect operating life and positioning performance.
Contact DLY
DLY supplies rolled and precision-ground ball screws for CNC machinery, industrial automation and other linear-motion applications. Send us the shaft diameter, lead, length, accuracy grade, end-machining drawing and operating conditions for a suitable recommendation.
