Alloy Steel Machining

DEK delivers alloy steel machining across 4140, 4340, 8620, 4130, 1215 and A514, holding general tolerances to ±0.005 mm and micro features to ±0.003 mm. No MOQ: a single prototype shaft and a production batch of gears follow the same quoting process.

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6
Grades Machined
±0.005mm
General Tolerance
3 Days
Prototype Lead Time

CNC turning of an alloy steel threaded part

ISO 9001:2015 Certified AS9100D and ISO 13485 certified

Machining Alloy Steel: When It Earns Its Place

Alloy steel earns its spot on a BOM when a part needs more fatigue strength, wear resistance or toughness than plain carbon steel delivers, usually after heat treatment brings out the added chromium, nickel or molybdenum. See alloy steel vs carbon steel for the trade-offs on cost and machinability.

The trade-off: alloy steel costs more than carbon steel, and many grades need heat treatment to reach full strength. When a part needs more hot-hardness or wear resistance than any alloy grade offers, our tool steel machining service covers A2, D2, H13, O1 and S7.

ISO 9001, AS9100D and ISO 13485 certified
In-house CMM inspection with traceability
On-time delivery rate above 98.6%
2,300+ OEM clients over 20+ years

Alloy Steel Grades We Machine

Six grades cover the shafts, gears, brackets and structural plate we quote most. Each card lists common designations and where the grade fits.

1215
G12150, EN1A, 11SMn30
1215 is a free-machining (resulfurized) steel for pins, shafts, fittings and high-volume turned parts, often ordered with alloy grades.
4130
AISI 4130, 25CrMo4, SCM430
Choose 4130 (1.7218) for tubing, brackets and fittings that need to be welded after machining.
4140
EN19, 42CrMo4, SCM440
4140 alloy steel machining covers shafts, gears and high-strength structural parts, annealed, normalized or quenched and tempered.
4340
EN24, 36CrNiMo4, 817M40
Specify 4340 (1.6511) for high-fatigue shafts and structural components that see repeated loading in service.
8620
G86200, 1.6523
8620 is the grade for case-hardened gears, bearings and wear surfaces where the surface takes the load.
A514
ASTM A514, T-1 Steel
A514 covers heavy structural plate and wear-resistant parts, with part sizes up to ~1000 mm.

Alloy steel part being machined with CNC tool

±0.005mm
General CNC machining
±0.01mm
5-axis complex profile
±0.003mm
Micro parts (sub-10 mm)
~1000mm
Max part size

Steel CNC Machining Capabilities & Tolerances

We hold each feature to the tolerance its process supports, not one blanket number: a turned OD, a milled pocket and a drilled bore each get their own.

1

3/4/5-Axis Milling

Prismatic alloy steel parts run on 3-, 4- and 5-axis mills; complex profiles cut with 5-axis machining hold ±0.01 mm.
2

CNC & Swiss Turning

Shafts, pins and bushings run on CNC and Swiss-type lathes; free-machining 1215 breaks chips cleanly for high-volume CNC turning.
3

Wire & Sinker EDM

Wire and sinker EDM sit in the same process stack as our mills and lathes, applied to alloy steel as to every other metal family.
4

Grinding & Gear Cutting

Precision grinding plus gear cutting for pinions and splines complete shafts and gears machined from 4140 or 8620.

Alloy Steel Machinability & Process Notes

What our engineers adjust in tooling, feeds and sequencing when a part moves from carbon steel to an alloy grade.

1

Work Hardening & Tool Wear

Alloy steels harden faster than plain carbon steel under the cutting edge, so we run tougher tooling, controlled feeds and closer coolant management to avoid premature tool wear.
2

Heat-Treat Condition Sets Cuts

Annealed or normalized 4140 machines reasonably well with standard carbide. Quenched and tempered, cutting forces and tool wear rise, so feeds, speeds and tool grade shift with it.
3

Free-Machining 1215

Added sulfur in 1215 breaks chips cleanly, which simplifies high-volume turned parts like pins and bushings.
4

Welding Higher-Alloy Grades

Some higher-alloy grades are harder to weld without pre- or post-heat treatment; for welded tubing, brackets and fittings, 4130 is the usual choice.

Alloy Steel Grade Datasheets

Open the page for 4130, 4140, 4340, 8620 or A514 to check designations and request a price for your part before you send the drawing.

Alloy Steel vs Carbon Steel, Tool Steel or Inconel

When plain carbon steel falls short, alloy steel is the usual step up; when alloy grades fall short on hot-hardness or corrosion, tool steel or Inconel take over.

Criteria	This MaterialAlloy Steel	Carbon Steel	Tool Steel	Inconel
Choose it for	Fatigue, toughness	Lower cost	Hot-hardness	Corrosion, heat
Wear	Higher	Lower	Above alloy	–
Cost	Higher	Lower	–	–
Machining	Hardens fast	Easier	Harder	–

Where Alloy Steel Parts Are Used

From drivetrain components to downhole tool parts, alloy steel goes where fatigue strength, wear resistance and toughness decide part life.

Surface Finishing Options for Alloy Steel

Every finish is applied to your CNC machined part and chosen by wear and corrosion requirements, not a one-size finish.

Steel Finishes

Black Oxide
Zinc or Nickel Plating
Nitriding
Powder Coating
Heat Treatment

Need a finish not listed here? Browse all surface finishes

Alloy Steel Machining FAQs

Answers to the questions engineers ask before specifying an alloy steel grade.

Is 4140 alloy steel easy to machine?

Yes, in its annealed or normalized state 4140 machines reasonably well with standard carbide tooling. Once it is quenched and tempered to higher hardness, cutting forces and tool wear increase, so feeds, speeds and tool grade need to shift with the heat-treat condition.

What is the hardest steel to machine?

Fully hardened tool steels and high-alloy grades with heavy chromium or tungsten content generally cut harder than standard alloy steels like 4140 or 8620. That is why they call for tougher carbide grades, lower speeds and more frequent tool changes.

What are the disadvantages of alloy steel?

Alloy steel costs more than plain carbon steel, is heavier than aluminum, and many grades need heat treatment to reach full strength, which adds a process step. Some higher-alloy grades are also harder to weld without pre- or post-heat treatment.