4140 Pre-Hardened Alloy Steel Bar — Factory Direct Supplier | Huaxia-Steel

4140 pre-hardened steel bar arrives at your machine shop already quenched and tempered to 28–32 HRC, so you skip the heat-treatment cycle, its distortion, and its lead time. For shafts, gears, pins, mould bases, and high-strength fasteners machined from 20–300 mm bar, buying pre-hardened (Q&T delivered) is the shortest and most repeatable route from stock to finished part. Huaxia-Steel supplies AISI 4140 / DIN 42CrMo4 pre-hardened round and flat bar with controlled hardness bands, EN 10204 3.1 certificates, and cut-to-length or rough-turned service.

Product Overview

Delivery condition: quenched (oil or polymer) and tempered, hardness 28–32 HRC (277–321 HB) standard; 32–36 HRC and 36–40 HRC bands available.

Surface options: hot-rolled black, peeled/turned bright, cold drawn, or ground and polished (h7/h8) for bushings and sleeve stock.

Diameter range: 16–300 mm round bar; flats to 200 mm wide × 100 mm thick; lengths 3–6 m, cut-to-size ±1 mm.

Equivalents: DIN 42CrMo4 / 42CrMoS4 (1.7225 / 1.7227), JIS SCM440, GB 42CrMo.

Standards: ASTM A29/A29M, ASTM A322, EN 10083-3; certs dual-listed to AISI and EN on request.

Specification Table

Parameter	Range / Value
Carbon	0.38–0.43%
Cr / Mo	0.80–1.10% / 0.15–0.25%
Tensile strength (Q&T, 28–32 HRC)	1000–1200 MPa
Yield strength (0.2%)	≥ 750 MPa (Ø ≤ 100 mm)
Elongation A5	≥ 12%
Impact (Charpy V, RT)	≥ 35 J typical
Diameter tolerance (peeled)	h9–h11 (−0.05/−0.10 mm on 50–100 mm)
Diameter tolerance (cold drawn)	h9; ground h7 on request
Straightness	≤ 1 mm/m standard; ≤ 0.5 mm/m for ground bar
Length	3000–6000 mm random; fixed length cutting service

Optional Grades and Related Alloys

Grade	Key Difference	When to Choose
4140 Q&T 28–32 HRC	Standard pre-hardened	General shafts, gears, mould bases
4140 SH (sulfurized, 42CrMoS4)	Added S 0.02–0.035%	High-volume machining, better tool life
4340 / 34CrNiMo6	1.65–2.0% Ni	Thick sections > 75 mm, impact/fatigue duty
4142 / 42CrMo4+	Carbon top of band	Extra core hardness in larger sections
SCM440 (JIS)	Equivalent chemistry, JIS certs	Japanese-standard projects

Manufacturing Standards

Bars are produced to ASTM A29 general requirements and A322 grade chemistry, heat treated in continuous or batch lines with temperature records retained per heat. Hardenability is confirmed by Jominy end-quench (ASTM A255) on representative heats — critical because two “4140” heats with identical chemistry can differ 10–15 mm in DI. Tempering temperature controls the delivered band: 560–600°C produces the standard 28–32 HRC; higher tempers trade hardness for toughness. All material ships with EN 10204 3.1 certificates listing heat analysis, mechanical results, hardness survey, and heat-treatment parameters.

Applications

Transmission shafts, spindles, axle components

Gears, racks, pinions (induction hardenable to 55 HRC surface)

Mould bases, tool holders, die holders for plastics tooling

High-tensile bolts, studs, and tie rods (property class 10.9–12.9)

Hydraulic cylinder rods and piston parts, machine ways

Quality Assurance

Hardness survey: 3 points per bar end, band 28–32 HRC enforced lot-wide

UT testing to SEP 1921 / ASTM A388 Class D on Ø ≥ 80 mm bar

Grain size ASTM E112 ≤ 5 (typ. 6–8) after Q&T

Decarb check per ISO 3887 ≤ 0.3 mm on black bar; none on peeled

Surface defect detection (eddy current) on bright bar production

Optional: third-party witness (SGS/BV/TÜV) and 3.2 certification

Packaging and Shipping

Bars are bundled ≤ 3 MT with steel strapping and end protection; peeled and ground bar is sleeved or paper-wrapped to protect the surface, with rust-preventative oiling for ocean freight. Each bundle carries heat number, grade, size, and hardness band tags matching the MTC. Cut-to-length pieces are packed in wooden crates (fumigated, IPPC marked) with piece-level marking. Export ex-works, FOB, CIF, or DAP — documentation set issued in English prior to shipment.