AISI 4140 Low-Alloy Steel

Material Profile: AISI 4140 Low-Alloy Steel for Binder Jetting

Binder Jetting Engineering Material Technical Report Series

Compiled from manufacturer technical datasheets and peer-reviewed literature

Abstract—AISI 4140 (UNS G41400) is a chromium-molybdenum medium-carbon low-alloy steel — a versatile, high-strength engineering steel widely used in automotive gear, drivetrain, and structural applications. It is qualified on the Desktop Metal Production System P-50 and customer-qualified on X-Series and Studio System BMD. Binder-jet 4140 was developed jointly by Desktop Metal and Hyundai Motors specifically for gearbox control finger production by automotive AM. After quench-and-temper heat treatment (oil-quench from 845 °C, temper at 540 °C), binder-jet 4140 achieves UTS ≈ 950 MPa, yield ≈ 800 MPa, hardness HRC 28–32, with > 12 % elongation. Its excellent fatigue performance, weldability, and machinability after quench-and-temper make 4140 the BJ material of choice for moderately loaded mechanical components where 17-4PH's stainless requirement is not needed.

Index Terms—additive manufacturing, binder jetting, 4140, low-alloy steel, chromoly, automotive gears, Desktop Metal Production System.

I.  MATERIAL IDENTIFICATION

This section establishes the canonical names and commercial designations under which the material is supplied.

A.  Designation

Trade names: Desktop Metal 4140 (Production / X-Series); Digital Metal DM 4140; ExOne 4140. Wrought equivalents: AISI/SAE 4140 (UNS G41400), ASTM A29 / A434, EN 1.7225 (42CrMo4), JIS SCM440. Common shop name 'chromoly' or '4140 chrome-moly'.

B.  Full Chemical Name

Chromium-molybdenum-carbon low-alloy steel. Composition (wt%): C 0.38–0.43, Cr 0.80–1.10, Mo 0.15–0.25, Mn 0.75–1.00, Si 0.15–0.35, P ≤ 0.035, S ≤ 0.040, Fe — balance. Strengthening: Q&T martensite (oil-quench + temper); fine carbide dispersion at the temper temperature.

C.  Aliases and Alternative Designations

II.  COMPOSITION AND MOLECULAR STRUCTURE

A.  Empirical Chemical Formula

Fe(balance) — C(0.38–0.43%) — Cr(0.80–1.10%) — Mo(0.15–0.25%) — Mn(0.75–1.00%) — Si(0.15–0.35%) — minor (P, S). Strengthening: Q&T martensite + fine Cr/Mo carbides after temper at 540 °C.

Fig. 1.  Repeating unit / structural schematic of the polymer matrix.

Fig. 2.  Schematic of the single-phase polymer (no reinforcement).

B.  Composition Breakdown

TABLE I
 COMPOSITIONAL BREAKDOWN OF 4140 LOW-ALLOY STEEL (DESKTOP METAL PRODUCTION) (TYPICAL / PER SUPPLIER DATASHEET)

III.  MECHANICAL PROPERTIES — XY BUILD DIRECTION (HORIZONTAL)

In the XY orientation the tensile load is applied parallel to the powder-bed plane. Binder-jetted (BJ) parts in the as-sintered state generally show modest in-plane vs build-axis anisotropy because sintering occurs near the solidus and re-distributes the porosity left by the binder-removal step. For metal BJ, post-sintering treatments (HIP, solution-anneal, age) are commonly applied to bring properties to wrought-equivalent and to eliminate residual closed porosity.

TABLE II
 MECHANICAL PROPERTIES — XY ORIENTATION (4140 LOW-ALLOY STEEL (DESKTOP METAL PRODUCTION))

IV.  MECHANICAL PROPERTIES — Z BUILD DIRECTION (VERTICAL)

In the Z orientation the tensile load is applied perpendicular to the printed layers. Binder-jet metal parts typically exhibit Z-direction strength within 5–15 % of XY in the as-sintered state, since the inter-layer interface effectively dissolves during high-temperature sintering. For sand-mould materials, Z-direction strength is dominated by inter-layer binder bonding and is generally 60–90 % of XY in transverse strength.

TABLE III
 MECHANICAL PROPERTIES — Z ORIENTATION (4140 LOW-ALLOY STEEL (DESKTOP METAL PRODUCTION))

Binder-jet 4140 has near-isotropic mechanical properties after Q&T. The austenitisation at 845 °C followed by oil-quench produces a uniform martensitic microstructure that is dimensionally and mechanically homogeneous. The tempering step at 540 °C / 1 h further homogenises by precipitating fine carbides uniformly throughout the matrix.

V.  RECOMMENDED PROCESS PARAMETERS

Values summarised below give consensus operating windows from public datasheets (Desktop Metal, ExOne, voxeljet, cprint3d). Specific machines and parameter sets may differ within ±10 %; the supplier's verified parameter sheet always supersedes this table. For metal binder jetting, complete green-state cure (~200 °C) and a high-temperature de-bind / sinter cycle (typically 1 100–1 380 °C in H₂ / Ar / vacuum) are mandatory after print. For sand binder jetting, parts are usable directly after print (with optional microwave or oven post-cure).

TABLE IV
 RECOMMENDED BINDER-JETTING PROCESS PARAMETERS FOR 4140 LOW-ALLOY STEEL (DESKTOP METAL PRODUCTION)

VI.  GLASS TRANSITION TEMPERATURE (TG)

Reported / typical Tg: Not applicable (metallic alloy).

Critical thermal limits: austenitisation 845 °C (Ac₁ ≈ 750 °C); martensite start Ms ≈ 280 °C; tempering range 200–650 °C (selectable); service temperature ≈ 425 °C continuous (above this, tempering progresses); melting range 1416–1454 °C.

VII.  HEAT DEFLECTION TEMPERATURE (HDT)

Heat deflection temperature is the temperature at which a standard bar deflects 0.25 mm under a specified flexural load (ASTM D648 / ISO 75).

TABLE V
 HEAT DEFLECTION TEMPERATURE OF 4140 LOW-ALLOY STEEL (DESKTOP METAL PRODUCTION) UNDER STANDARD TEST LOADS

VIII.  DISTINGUISHING CHARACTERISTICS AND STANDARDS

A.  Versatile mid-strength engineering steel

4140 occupies the sweet spot of strength (UTS ≈ 950 MPa Q&T), toughness (Charpy ≈ 35 J), machinability, weldability, and cost — attributes for which it has dominated automotive and machinery applications for decades. Binder-jet 4140 brings these proven properties to AM at a fraction of laser PBF cost.

B.  Excellent hardenability

Through-hardening to large section sizes (≥ 25 mm dia.) due to Cr+Mo content. Gear teeth, shafts, and structural sections produced by BJ + oil-quench reach HRC 30 throughout the section, not just at the surface.

C.  Hyundai-validated application

Hyundai Motors and Digital Metal jointly developed binder-jet 4140 for gearbox 'control finger' components — a high-volume automotive application where lead time and tooling cost dominate. Documented case study: BJ 4140 control fingers replaced sand-cast + machined parts at 30 % lower total cost.

D.  Heat-treatment flexibility

Same printed green part can be tempered at 200 °C (HRC 50, hard but brittle), 540 °C (HRC 30, balanced — most common), or 650 °C (HRC 22, high ductility — for parts that will be cold-formed). Single inventory SKU, multiple end-use property profiles.

E.  Limitations vs 17-4PH and stainless

4140 is NOT corrosion-resistant — it rusts in ambient humid environments and requires painting, plating, or oil coating. For corrosion service, specify 17-4PH or 316L. 4140 is also not appropriate for biomedical use (no biocompatibility certification).

IX.  REPRESENTATIVE APPLICATIONS

4140 Low-Alloy Steel (Desktop Metal Production) is typically deployed in the following applications:

1)  Automotive drivetrain components: Gearbox shafts, gear blanks, control fingers, spline shafts — leveraging 4140's fatigue performance and through-hardenability.

2)  Industrial machinery shafts: Drive shafts, key shafts, machine axles where moderate strength + toughness combine.

3)  Hydraulic and pneumatic cylinders: Cylinder bodies, piston rods — 4140 is the standard wrought hydraulic cylinder material.

4)  Tooling (non-hot-work): Punches, dies, jigs for moderate-cycle cold-work applications; not for hot-work (use H13 instead).

5)  Structural fasteners and brackets: High-strength bolts, custom brackets — galvanised or oil-coated for corrosion protection.

X.  REFERENCES

[1]  Digital Metal, “DM 4140 Low-Alloy Steel — Material Profile,” 2021. [Online]. Available: https://www.metal-am.com/digital-metal-adds-low-alloy-steel-and-superalloy-to-range-of-bjt-materials/

[2]  Desktop Metal, “4140 Low-Alloy Steel — Material Data Sheet (Production System),” 2024.

[3]  ASTM A29/A29M-20, “Standard Specification for General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought,” 2020.

[4]  AISI/SAE 4140, “Heat Treatment of Carbon and Alloy Steels,” SAE J412.

[5]  EN 10083-3:2006, “Steels for quenching and tempering — Part 3: Technical delivery conditions for alloy steels,” CEN.

[6]  ASTM E8/E8M-22, “Standard Test Methods for Tension Testing of Metallic Materials,” ASTM International, 2022.

[7]  ASTM B962-17, “Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes' Principle,” ASTM International, 2017.

[8]  ASTM E18-22, “Standard Test Methods for Rockwell Hardness of Metallic Materials,” ASTM International, 2022.

[9]  ASTM F3318-22, “Standard for Additive Manufacturing — Finished Part Properties — Specification for AlSi10Mg with Powder Bed Fusion — Laser Beam,” ASTM International, 2022.

[10]  ISO/ASTM 52900:2021, “Additive manufacturing — General principles — Fundamentals and vocabulary,” ISO, 2021.

[11]  ISO/ASTM 52904:2024, “Additive manufacturing — Process characteristics and performance — Practice for metal powder bed fusion process to meet critical applications,” ISO, 2024.

[12]  MPIF Standard 35-MIM, “Materials Standards for Metal Injection Molded Parts,” Metal Powder Industries Federation, 2022 ed.

[13]  Desktop Metal, “Material Properties of Binder Jet Parts,” Desktop Metal Technical White Paper. [Online]. Available: https://www.desktopmetal.com/resources/material-properties-of-binder-jet-parts

[14]  Desktop Metal, “Why Binder Jetting?” Desktop Metal Application Note. [Online]. Available: https://www.desktopmetal.com/resources/why-binder-jetting-1

[15]  Desktop Metal, “Materials portfolio overview,” Desktop Metal product page. [Online]. Available: https://www.desktopmetal.com/materials/

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