The main differences are surface hardness, corrosion resistance and which bearing types they can safely work with.

1. Hardened carbon steel shafts (45# / SUJ2 / CF53)

• Typical material and treatment

  • Medium/high carbon steel or bearing steel (45#, SUJ2, CF53, etc.)

  • Usually induction hardened on the surface to about HRC 60–64

  • For industrial use, they are almost always hard chrome plated (hard chrome shaft), so they are not “bare raw steel".

• Best suited for

  • About 90% of industrial automation: CNC machines, linear modules, 3D printers, packaging, handling, etc.

  • Any application using standard linear ball bearings (LM, LME series).

• Bearing compatibility

  • Hardened, chrome-plated surface with HRC 60+ is a perfect match for steel linear ball bearings.

  • Ball hardness and shaft hardness are similar, so the surface can withstand the point contact stress without grooving.

• Corrosion behaviour

  • The hard chrome layer provides basic corrosion protection in indoor and normal workshop environments.

  • In outdoor, splash water or aggressive environments they can still rust and may need extra protection (grease, wipers, boots).

2. 304 stainless steel shafts (soft stainless)

• Material characteristics

  • Austenitic stainless steel (304) cannot be through-hardened by heat treatment.

  • Typical surface hardness is only around HRC 20–25, much softer than bearing steel.

• Best suited for

  • Food, beverage and pharmaceutical machinery

  • Medical and semiconductor equipment

  • Wet, hygienic or chemically aggressive environments where corrosion resistance is critical and loads are light to medium.

• ⚠ Critical warning: do NOT pair 304 shafts with standard steel linear ball bearings long term

  • Steel balls in LM-type bearings are typically around HRC 60.

  • When hard balls roll on a soft HRC 20–25 shaft under load, the contact stress is very high →

    • The balls will quickly indent and groove the shaft surface (Brinelling / grooving).

    • Precision, smoothness and shaft life drop dramatically.

  • 304 stainless shafts are not meant to be used as “soft rails" for steel ball bearings in heavy or continuous-duty applications.

• Correct pairings for 304 shafts

  • Polymer bearings / plastic bushings (e.g. IGUS-type)

  • Bronze / brass plain bushings
    These materials are softer than the shaft and distribute load better, so they will not destroy the 304 surface and can work in wet, washdown or no-lubrication conditions.

3. Need both hardness and corrosion resistance?

If you need:

• High load capacity with steel linear ball bearings, and

• Better corrosion resistance than chrome-plated carbon steel,

then consider:

• 440C martensitic stainless steel shafts

  • Can be heat-treated to HRC ~58+

  • Offer a compromise between stainless behaviour and high hardness

  • More expensive than 45#/SUJ2 shafts and usually treated as a premium option.

Practical summary

• Use hardened 45#/SUJ2/CF53 chrome-plated shafts for most industrial axes with LM/LME linear ball bearings.

• Use 304 stainless shafts mainly when corrosion resistance and hygiene are more important than high load and long-life with ball bearings, and pair them with polymer or bronze bushings, not standard steel linear ball bearings.

• If you need a fully stainless system with ball bearings and high load, look for 440C stainless shafts and matching stainless linear bearings.