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Alloy Steel · General Oilfield + Industrial
4140 & 4340 CNC Machining
Chromium-molybdenum alloy steels — the general-purpose workhorses of oilfield, industrial, and defense CNC machining. Pre-hardened (~28–32 HRC) 4140 is a standard oilfield bar; 4340 adds nickel for higher toughness in critical applications.
4140 / 4340 Alloy Steel at a glance
| UNS 4140 | G41400 |
| UNS 4340 | G43400 |
| Hardness (4140 pre-hard) | ~28–32 HRC |
| Yield strength (4140 pre-hard) | ~95 ksi |
| Yield strength (4340 Q&T) | ~110 ksi |
| Machinability rating | Good (pre-hard) to excellent (annealed) |
Conditions we routinely machine:
AnnealedNormalizedPre-hardened (28–32 HRC)Q&T to spec
Where we machine 4140 / 4340 Alloy Steel
Capabilities
Industries served
Typical 4140 / 4340 Alloy Steel parts
- General oilfield adapters and subs
- Industrial shafts and pinions
- Wellhead pre-hard bar work
- Defense structural hardware
- Machine spindles and drive components
Frequently asked questions
What's the difference between 4140 and 4340?
4340 adds nickel (~1.8%) for higher toughness and hardenability. 4140 is more common and cheaper; 4340 is spec'd when the application needs the extra impact toughness.
Do you machine pre-hardened 4140?
Weekly. Pre-hard 4140 is the standard oilfield bar spec — 28–32 HRC out of the mill, no post-machining heat treat needed.