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Should I use 4140 or 1045 steel?
Use 1045 for moderately loaded shafts, pins and induction-hardened parts; it costs less and forges easily. Use 4140 when sections are thick, loads are high or cyclic, or you want pre-hard 28–32 HRC bar with no heat treat. Chromium and molybdenum let 4140 quench and temper to 28–50 HRC through 2–3 in (50–75 mm) sections, where 1045 hardens fully only below about 1 in (25 mm).
Steel 4140 (annealed)
Steel 1045 (cold drawn)
By the numbers
Priced on the same representative part: flanged bushing, forging, 2,500 pcs.
Tensile strengthMPa
4140
655
1045
625
Yield strengthMPa
4140
415
1045
530
Densityg/cm³
4140
7.85
1045
7.87
Elongation%
4140
25.7
1045
12
Raw material cost$/kg
4140
3.2
1045
2.4
Which should you pick?
Pick 4140 when
- Sections over about 1 in (25 mm) need through-hardness
- Loads are high, cyclic or shock
- You want pre-hard 28–32 HRC bar machined complete with no heat treat
- A nitrided wear surface with little distortion is the plan
Pick 1045 when
- Only the surface needs hardening, by induction or flame
- Sections are under about 1 in (25 mm)
- Loads are moderate and cost matters
- The part is a simple forged lever or link
Key differences
| 4140 | 1045 | |
|---|---|---|
| Alloying | Chromium-molybdenum, 0.38–0.43% carbon | Plain carbon, 0.43–0.50% carbon |
| Hardenability | 28–50 HRC through 2–3 in (50–75 mm) sections | Full hardness only under about 1 in (25 mm) |
| Pre-hard stock | 28–32 HRC bar widely stocked | Not a common stock condition |
| Welding preheat | 400–600 °F (200–315 °C) plus post-weld stress relief | 300–500 °F (150–260 °C) |
| Surface hardening | Induction, flame or nitriding to about 500–600 HV | Induction or flame to 55–60 HRC |
| Relative cost | About 30% more | Baseline |
Questions
Is 4140 stronger than 1045?
It depends on condition. Annealed 4140 at about 95 ksi (655 MPa) and cold drawn 1045 at about 91 ksi (625 MPa) are close. After quench and temper, 4140 commonly reaches 140 ksi (965 MPa) or more through thick sections, which 1045 cannot match.
What is 4140 pre-hard?
Bar the mill has already quenched and tempered to about 28–32 HRC, roughly 130–145 ksi (900–1,000 MPa) tensile. It machines slower than annealed stock but needs no heat treat afterward, so there is no distortion or scale to clean up.
Is 4140 harder to machine than 1045?
Annealed 4140 machines about as well as cold drawn 1045, rated 65 versus 55. Pre-hard 4140 cuts slower, and above about 35 HRC machining gets slow, so rough before hardening.
Try both on your part.
The builder prices the same geometry in every suitable process and material, with DFM for each.