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4140 1.7225 SCM440 alloy structural steel

4140 alloy structural steel offers excellent strength, good hardenability, and high fatigue resistance. With good toughness and wear resistance, ideal for heavy-duty shafts, gears, connecting rods, and other high-stress structural components.

Standard: AISI 4140, DIN 1.7225(42CrMo4), JIS SCM440, GB 42CrMo
Technique: EAF + LF + VD, forged or hot-rolled, multi-directional forging ratio ≥4, normalized and tempered or quenched and tempered as required
Shape: Round, Flat, Plates, Blocks
Heat treatment: Supplied in quenched and tempered (QT) condition with hardness 28–34 HRC typical; annealed or normalized condition available on request
Surface Treatment: Turned, milled / ground, sawn ends. Black (hot-rolled / forged surface) available for large sections
Tolerance: flat bars & plates thickness: +0.5/-0.0 mm (turned); forged blocks: ±0.2 mm
MOQ: 1 Ton

We supply AISI 4140 in various custom sizes

Chemical Composition (%)

Grade	C	Si	Mn	P (≤)	S (≤)	Cr	Mo
4140	0.38–0.43	0.15–0.35	0.75–1.00	0.035	0.035	0.80–1.10	0.15–0.25
1.7225	0.38–0.45	≤0.40	0.60–0.90	0.035	0.035	0.90–1.20	0.15–0.30
42CrMo4	0.38–0.45	≤0.40	0.60–0.90	0.035	0.035	0.90–1.20	0.15–0.30
SCM440	0.38–0.43	0.15–0.35	0.60–0.90	0.035	0.035	0.90–1.20	0.15–0.30
42CrMo	0.38–0.45	0.17–0.37	0.50–0.80	0.030	0.030	0.90–1.20	0.15–0.25

Main characteristics of 4140 Alloy Steel

4140 | 1.7225 | SCM440 Alloy Steel applications

4140 steel for Drive Shaft & Transmission Gear

High torsional strength and fatigue resistance ensure reliable power transfer and long service life under constant cyclic loads.

4140 steel for Oil Field Tool Joint & Drill Collar

Deep hardenability and excellent toughness withstand extreme downhole stresses and corrosive environments, preventing premature failure.

4140 steel for Landing Gear Component

Superior impact strength and structural integrity under high shock loads make it ideal for critical aircraft landing gear components.

Our Production Technology For 4140 (1.7225 / 42CrMo4 / SCM440) Engineering Alloy Steel

Ultrasonic testing (UT) as per ASTM A388 or SEP 1921 (upon request)
Micro Cleanliness as per ASTM E45
Grain size ≥ 6 ASTM E112 for critical applications
Delivery condition options:
Annealed: max. 230 HB (easily machinable)
Normalized: approx. 300 HB (refined grain structure)
Prehardened (Tempered) : 18–32 HRC (ready for immediate machining), or 269–331 HB (high strength)
Mechanical properties as per ASTM A29 / ASTM A322 or EN 10083-3

mechanical properties & heat treatment of 4140 steel

Heat temperature	Start forging temperature	Finish forging temperature	Cooling method
1150 – 1200 °C	1150 – 1100 °C	≥ 850 °C	Pit, sand, or furnace cooling

Annealing

Hardening

4140 alloy steel can be hardened in oil, water, polymer or air, depending on section size and quenching equipment. Proper preheating and austenitizing are critical to achieve the desired hardness without cracking
Pre-heating (recommended): Preheat to 550 – 650°C to reduce thermal shock during austenitizing
Austenitizing temperature: 840 – 875°C.
For thinner sections: lower end of the range (840–850°C).
For thicker sections: upper end of the range (860–875°C)
Holding time: 10 – 15 minutes per 25mm of section thickness
Quenching media (select based on section and geometry) :
Oil (most common — provides good hardness with moderate distortion)
Water (faster quench — for larger sections, but increases distortion and crack risk)
Polymer (medium quench rate — good for mediumsized components)
Hardness after quenching: approx. 55 HRC (510 HB) at the surface

Stress relieving

Perform after rough machining, heavy stock removal or welding to reduce residual stresses
Heat carefully to 680 – 700°C
Hold for 1 hour per 25mm of section thickness (minimum 2 hours)
Air cool after holding
This operation reduces distortion risk during final hardening and improves dimensional stability

Tempering

Temper immediately after the workpiece cools to handwarm temperature (approx. 50–70°C). Delayed tempering may cause cracking
Number of tempers: Minimum 2 times for critical components. Double tempering improves impact toughness and ensures stable properties
Holding time: 1 hour per 25mm of section thickness (minimum 2 hours)
Cooling method: Air cool after each tempering cycle
Tempering temperature range: 150 – 700°C, depending on final hardness requirement

Why Choose NSPM as Your 4140 Alloy Steel Supplier

Source Direct

Direct mill cooperation ensures stable supply, competitive pricing, and consistent quality. Global resource integration and strong supply chain management guarantee reliable material sourcing and long-term availability.

Stock Ready

50,000+ tons inventory across 11 warehouses enables fast delivery. Flexible cutting, short lead times, and ready stock support urgent demands and improve customers’ production efficiency.

Expert Team

600+ professionals, including R&D specialists and technical engineers, provide application-driven support. Fast response and deep tooling knowledge ensure accurate solutions for diverse industrial needs.

Fully Inspected

Strict quality control system with full traceability, UT testing, and heat treatment records. Certified standards (ISO, CE) ensure every material meets high-performance and reliability requirements.

Full-Chain Machining

From steel supply to precision machining, heat treatment, and equipment manufacturing, NSPM offers integrated solutions that enhance accuracy, efficiency, and overall tooling performance.