4140 Alloy Steel Shafts

Chrome-moly alloy steel — the go-to when the part genuinely needs wear resistance and tensile strength.

At a glance

Stocked condition	Cold finished, annealed (CFA)
Machinability	Moderate (annealed)
Weldability	Weldable with preheat and post-heat — plan it, don't improvise it
Corrosion resistance	Low — protect it like any carbon/alloy steel
Hardening	Through-hardens; oil quench and temper to customer spec
Density (nominal)	0.284 lb/in³
Food contact	No
Magnetic	Yes

4140 is the standard high-strength shafting alloy: chromium and molybdenum give it deep hardenability, so it through-hardens in shaft-size sections rather than just skinning over. We stock it cold finished and annealed, which machines predictably and leaves your heat treater a clean starting condition.

The usual flow is machine → harden and temper to the customer's spec → grind critical journals if the tolerance demands it. If you would rather skip heat treat entirely and can live with as-supplied strength, look at 1144 stress-relieved first.

Configure a 4140 part →

Any geometry in the configurator — diameters, threads, keyseats, grooves, holes, tapers — can be machined in 4140. Pick the material in the sidebar and the price updates live.

When to choose 4140

The load case demands through-hardened strength or wear resistance.
High-torque, shock, or fatigue duty: gearbox, spindle, and heavy drive shafts.
You have a heat-treat step in the process plan already.

Consider instead

1144 — strong as-supplied with no heat-treat step.
1045 — cheaper when only local induction hardening is needed.
17-4 PH — when you need the strength plus corrosion resistance.

Typical applications

Gearbox and reducer shafts
Spindles and arbors
Heavy-duty drive and axle shafts
Tooling and die shanks

Ready-made starting points in this material's wheelhouse: ANSI pump shafts · Gearbox plug-in output shafts.

Frequently Asked Questions

We machine it in the annealed condition; hardening happens after machining, by you or your heat treater, to the exact hardness your application needs. That order of operations protects the machined tolerances.

Yes, but only with proper preheat and post-weld heat treatment — its hardenability that makes it strong also makes uncontrolled welds crack. If casual welding is expected, 1018 is the safer design choice.

1144 stress-relieved delivers near-alloy strength with zero heat treat and better machinability, so it often wins on cost and lead time. 4140 wins when the part must be through-hardened, sees impact, or needs alloy toughness at temperature.

Stocked as 4140 CFA — cold finished, annealed. Material and condition are paired — each grade ships in one condition optimized for our process; see all grades on the materials page.