Feed & Speed Calculator for 4140 Steel
A tougher, higher-strength alloy steel than 1018 — and one where knowing whether your stock is annealed or heat-treated matters more than any other single fact.
4140 starting ranges
| Condition | Cutting speed, carbide (SFM) | Chip load, 1/2" 4-flute (in) |
|---|---|---|
| Annealed (soft, <220 HB) | 250–400 | 0.002–0.004 |
| Normalized / pre-hard (28–32 HRC) | 150–250 | 0.002–0.003 |
| Q&T hardened (38–45 HRC) | 60–120 | 0.001–0.002 |
These three conditions are not interchangeable — running annealed-material speeds on hardened 4140 will burn a tool fast. Check the actual hardness before picking a row.
4140 is really three different materials to a cutting tool
Unlike 1018, 4140 is commonly stocked and sold in multiple heat-treat conditions — annealed (soft, easy to machine), normalized or "pre-hard" (moderate hardness, a common compromise for parts needing some strength without a separate heat-treat step), and fully quenched-and-tempered (genuinely hard, tough on tools). The same nominal alloy behaves like three different materials depending which one you have.
Know your hardness before you pick a speed
If the mill certification or a hardness test isn't available, don't assume — annealed 4140 and Q&T 4140 call for roughly a 3–4× difference in cutting speed, and guessing wrong in the aggressive direction burns tools fast on hardened stock. When in doubt, start at the hardened-condition numbers and work up once you've confirmed the material cuts easier than expected.
Why 4140 shows up in high-stress parts
4140's chromium-molybdenum alloying gives it good toughness and hardenability through its cross-section, not just at the surface — that's why it's a common choice for shafts, gears, and structural components that need real strength, as opposed to 1018's use in general non-critical parts. Expect it to machine noticeably tougher than 1018 even in its softest, annealed state.
Find It on Amazon
Search Amazon directly for tooling, gauges, and shop supplies.