Technical Specification · Free Download

4140 Chromoly Alloy Steel – Technical Material Specification for Canadian Fabrication & Machining

Comprehensive technical specification for 4140 chromoly alloy steel, covering Canadian stock sizes, machinability, heat treatment, common defects, and storage guidelines for fabrication and machining shops.

Material Overview & Common Uses

4140 chromoly (chromium-molybdenum) alloy steel is a low-alloy, through-hardening steel known for its excellent balance of strength, toughness, and wear resistance. It is widely used in Canadian manufacturing for shafts, gears, axles, bolts, hydraulic components, tool holders, and structural parts requiring high fatigue strength. Typical supply condition is annealed (HB 197–235) or quenched and tempered (HB 280–350). Common Canadian stock includes hot-rolled (HR) and cold-finished (CF) rounds, flats, squares, and plate.

Core Technical Properties & Sizing

Property	Value / Specification
Chemical Composition (wt%)	C 0.38–0.43, Mn 0.75–1.00, Cr 0.80–1.10, Mo 0.15–0.25, Si 0.15–0.30, S ≤0.040, P ≤0.035.
Mechanical Properties (annealed)	Tensile strength 655–850 MPa, Yield strength 415–620 MPa, Elongation 25% min, Hardness HB 197–235.
Mechanical Properties (Q&T 300°C)	Tensile strength 1620 MPa, Yield strength 1450 MPa, Hardness HRC 48–52.
Standard Stock Sizes (round bar)	1/4" to 12" diameter, 12' or 20' random lengths. Common metric: 6 mm to 300 mm diameter, 3 m or 6 m lengths.
Standard Stock Sizes (flat bar & plate)	Flat: 1/4" x 1" up to 4" x 12", 20' lengths. Plate: 3/16" to 6" thick, 48" x 96" or 48" x 120".
Tolerances (cold-finished round)	Diameter tolerance ±0.002" for sizes up to 2", ±0.003" for 2"–4", ±0.005" for over 4". Straightness 1/16" in 10'.
Tolerances (hot-rolled round)	Diameter tolerance ±0.010" for sizes up to 2", ±0.015" for 2"–4", ±0.020" for over 4". Straightness 1/8" in 10'.
Density & Modulus of Elasticity	Density: 7.85 g/cm³ (0.283 lb/in³). Modulus: 205 GPa (30 x 10⁶ psi).

Machinability, Tooling & Feeds

Parameter	Recommendation / Value
Machinability Rating	65–70% of 1212 free-machining steel (annealed condition).
Cutting Speed (turning, carbide inserts, annealed)	120–180 SFM (37–55 m/min).
Feed Rate (turning, carbide inserts, annealed)	0.008–0.015 in/rev (0.20–0.38 mm/rev).
Depth of Cut (turning, carbide inserts, annealed)	0.050–0.150 in (1.3–3.8 mm).
Drilling Speed (HSS drills, annealed)	60–80 SFM (18–24 m/min).
Drilling Feed (HSS drills, annealed)	0.004–0.008 in/rev (0.10–0.20 mm/rev).
Coolant Type	Water-soluble oil flood coolant.
Tapping Recommendation	Use spiral point taps with TiN coating.
Pre-heat for Heavy Cuts	300–400°F (150–200°C) to reduce internal stress.
Post-Machining Stress Relief	1100–1200°F for 1 hour per inch of thickness, slow cool. Recommended for tight tolerances.

Common Defects & Quality Control

Defect / Check	Specification / Action
Surface Decarburization (soft skin)	Common on hot-rolled bars. Reject if depth exceeds 0.010" per side.
Centerline Porosity	Common in larger diameters. Perform ultrasonic testing (UT) for critical applications.
Laps & Seams (rolling defects)	Inspect visually. Reject if surface defects exceed 0.005" depth.
Quench Cracks (heat-treated stock)	Perform visual and MPI (magnetic particle inspection).
Incoming Hardness Verification	Use portable hardness tester (HRB or HB).
Incoming Dimensional Verification	Measure diameter with micrometer at three points along length.
Surface Condition Inspection	Visual check for pits, scratches, and excessive scale.
Traceability Requirement	Material Test Reports (MTR) must be traceable to heat number.

Storage, Handling & Racking Guidelines

Store indoors in dry, covered area. Use A-frame racks for round bars to prevent bending. Support long bars every 4–5 ft.
Flat bar and plate should be stored flat on wooden dunnage to avoid moisture contact.
Do not stack dissimilar metals directly (risk of galvanic corrosion).
Apply light oil (e.g., LPS 3) for long-term storage. Rotate stock FIFO to avoid surface rust.
For heat-treated material, store away from welding areas to prevent hydrogen embrittlement.
Handle with nylon slings or padded clamps to avoid surface damage.