What is the machinability rating of AISI 4340?

50 %, on the scale where AISI 1112 free-machining steel is 100%. Values above 100% mean the material cuts more easily than the reference steel; values below mean it is harder to cut. The rating is a comparison scale, not a physical property, so sources differ by roughly ±10%.

What cutting speed should I use for AISI 4340?

Typical ranges are 180–280 SFM (55–85 m/min) for rough turning and 280–380 SFM (85–115 m/min) for finishing, with milling around 180–320 SFM. These are starting points only — the correct value depends on the insert grade and coating, the depth of cut, rigidity of the setup, coolant and the machine. Start at the low end and increase until tool life or finish degrades.

What is the equivalent of AISI 4340 in other standards?

See the Equivalent Designations table above. Cross-standard correspondence is approximate: alloys within a designation are close but not guaranteed interchangeable, because each standard specifies its own composition ranges and tolerances. Verify against the specific specification before substituting.

What material group is AISI 4340?

P — Steel, sub-group Alloy steel, Ni-Cr-Mo. Material groups — P, M, K, N, S and H — classify materials by machining behaviour so that insert grades can be selected by group rather than by individual alloy.

AISI 4340

Machining data for AISI 4340 (Nickel-Chrome-Moly Steel) — material group, hardness, machinability rating, recommended cutting speeds and equivalent designations.

Data verified 2026-09-29 · based on n/a — industry comparison scale, no governing standard

Quick Answer

AISI 4340 has a machinability rating of 50 % and a hardness of 217–255 HB (annealed). Typical roughing speed is 180–280 SFM, finishing 280–380 SFM. It belongs to material group P.

General Information

Material group	P — Steel
Sub-group	Alloy steel, Ni-Cr-Mo
Hardness	217–255 HB (annealed)
Tensile strength	1,280 MPa (186 ksi)
Machinability	50 %
Density	7.85 g/cm³

High-strength nickel-chromium-molybdenum steel with deep hardenability and excellent toughness at strength. Used for aircraft landing gear, crankshafts and heavy-duty gearing. Machining cost is high because of its strength.

Cutting Speed Recommendations

Operation^[5]	Speed range (carbide)^[5]
Turning — roughing	180–280 SFM (55–85 m/min)
Turning — finishing	280–380 SFM (85–115 m/min)
Milling	180–320 SFM
Drilling (HSS)	45–65 SFM

Speeds are surface feet per minute with carbide tooling; millimetre equivalents are in brackets. These are typical catalogue ranges, not a specification. Depth of cut, feed, insert grade, coolant and machine rigidity all shift the correct value — start at the low end.

Equivalent Designations

Standard^[3]	Designation^[3]
AISI/SAE	4340
UNS	G43400
DIN	1.6582 (34CrNiMo6)
EN	34CrNiMo6
JIS	SNCM439

Cross-standard correspondence is approximate. Verify against the governing specification before substituting one designation for another.

Chemical Composition

Element^[1]	Content (%)^[1]
C	0.38–0.43
Mn	0.60–0.80
Ni	1.65–2.00
Cr	0.70–0.90
Mo	0.20–0.30
Fe	Balance

Composition limits per the governing specification for this grade. Ranges shown are the specification window, not a typical analysis.

Weight & Volume Calculator

Shape

Diameter (mm)

Length (mm)

Machining Notes

What Machinability Rating Means

The rating compares how easily a material cuts against AISI 1112 free-machining steel, which is defined as 100%. It folds together chip formation, surface finish, tool wear and power consumption into one number — it is a shop-floor comparison, not a physical property.

Two consequences follow. First, ratings from different sources differ by roughly ±10%, because each was measured under different conditions. Second, a high rating does not mean the material is soft: gray cast iron rates 70% and machines easily because the graphite breaks chips, while pure copper rates only 20% and is soft but gummy.

Use the rating to compare two candidate materials, not to predict a cutting speed. For speeds, use the table above and your own tooling catalogue.

Frequently Asked Questions

What is the machinability rating of AISI 4340?: 50 %, on the scale where AISI 1112 free-machining steel is 100%. Values above 100% mean the material cuts more easily than the reference steel; values below mean it is harder to cut. The rating is a comparison scale, not a physical property, so sources differ by roughly ±10%.
What cutting speed should I use for AISI 4340?: Typical ranges are 180–280 SFM (55–85 m/min) for rough turning and 280–380 SFM (85–115 m/min) for finishing, with milling around 180–320 SFM. These are starting points only — the correct value depends on the insert grade and coating, the depth of cut, rigidity of the setup, coolant and the machine. Start at the low end and increase until tool life or finish degrades.
What is the equivalent of AISI 4340 in other standards?: See the Equivalent Designations table above. Cross-standard correspondence is approximate: alloys within a designation are close but not guaranteed interchangeable, because each standard specifies its own composition ranges and tolerances. Verify against the specific specification before substituting.
What material group is AISI 4340?: P — Steel, sub-group Alloy steel, Ni-Cr-Mo. Material groups — P, M, K, N, S and H — classify materials by machining behaviour so that insert grades can be selected by group rather than by individual alloy.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	Chemical composition limits	standard	n/a — composition limits are taken from whichever specification applies to the grade — source
[2]	Values computed from the nominal figure	derived	Metric equivalents and any converted values are computed at build time; source values are the inch/imperial figures.
[3]	Equivalent international designations	standard	n/a — correspondence table, not a revisioned document — source
[4]	Machinability rating (AISI 1112 = 100%)	standard	n/a — long-established industry comparison scale — source
[5]	Recommended cutting speed ranges	standard	n/a — typical catalogue ranges with no single revision — source

Data Sources

Standard	Revision	What it covers on this page
Machinability rating, AISI 1112 = 100%	n/a — industry comparison scale, no governing standard	the machinability column
Tooling manufacturer cutting-speed recommendations	n/a — typical catalogue ranges	the cutting speed table
Grade specifications (ASTM / EN / DIN / JIS)	n/a — see the individual grade specification (ASTM, EN or DIN)	composition limits and equivalent designations

Cross-checked against:

Machinability ratings cross-checked against published machinability charts
Cutting speeds cross-checked against two tooling manufacturers' catalogues
Composition limits cross-checked against the governing ASTM and EN specifications

Cutting speeds vary with tooling and setup. The ranges shown are starting points for carbide tooling — confirm against the insert manufacturer's recommendation for the specific grade and geometry before production use.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "AISI 4340 — Machining Data." https://refmanual.com/materials/aisi-4340/ (accessed 2026-09-29). Data from Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale, no governing standard.

BibTeX

@misc{aisi-4340,
  title        = {AISI 4340 — Machining Data},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/materials/aisi-4340/}},
  note         = {Accessed: 2026-09-29},
  source       = {Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale, no governing standard}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - AISI 4340 — Machining Data
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/materials/aisi-4340/
PY  - 2026
DA  - 2026-09-29
N1  - Source: Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale, no governing standard
ER  -

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.