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4340 34CrNiMo6 SNCM439 alloy structural steel

4340 alloy structural steel offers excellent strength, deep hardenability, and high fatigue resistance. With good toughness and ductility, ideal for heavy-duty shafts, gears, landing gear components, and other high-stress structural applications.

Standard: AISI 4340, DIN 34CrNiMo6 (1.6582),JIS SNCM439, GB 40CrNiMoA
Technique: EAF + LF + VD, forged or hot-rolled, multidirectional forging ratio ≥4, 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 (hotrolled / 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 4340 in various custom sizes

Chemical Composition (%)

Grade	C	Si	Mn	P (≤)	S (≤)	Cr	Ni	Mo
4340	0.38–0.43	0.15–0.35	0.60–0.80	0.035	0.035	0.70–0.90	1.65–2.00	0.20–0.30
1.6582 (34CrNiMo6)	0.30–0.38	≤0.40	0.50–0.80	0.035	0.035	1.30–1.70	1.30–1.70	0.15–0.30
SNCM439	0.36–0.43	0.15–0.35	0.60–0.90	0.030	0.030	0.60–1.00	1.60–2.00	0.15–0.30
40CrNiMoA	0.37–0.44	0.17–0.37	0.50–0.80	0.025	0.025	0.60–0.90	1.25–1.65	0.15–0.25

Main characteristics of 4340 alloy steel

4340 | 34CrNiMo6 | SNCM439 alloy steel applications

4340 steel for Aircraft Landing Gear

High strength and fracture toughness absorb severe landing impact and cyclic stress, ensuring maximum structural safety.

4340 steel for Engine Rotor Component

Excellent high-temperature strength and fatigue resistance ensure rotor reliability under extreme centrifugal loads and thermal cycling.

4340 steel for Heavy-Duty Drive Shaft & Gear

Superior torsional strength and impact toughness deliver reliable power transmission under sustained heavy cyclic loads.

Our Production Technology For 4340 (34CrNiMo6 / 1.6582 / SNCM439) High-Strength Alloy Steel

EAF
LF
VD
ESR
VIM + VAR
Forged, Hot Rolled, or Cold Drawn
Annealed / Normalized / Quenched and Tempered (as specified)
Machined surface / Peeled / Black finish

Ultrasonic testing (UT) 100% as per SEP 1921, ASTM A388, or EN 10228-3 (upon request)
Micro Cleanliness as per ASTM E45 or DIN 50602 (upon agreement)
Grain size as per ASTM E112 (typical ≥ 5 for critical applications)
Delivery condition options:
Soft annealed (+A): max. 235–248 HB
Normalized (+N): approx. 363 HB
Quenched and tempered (+QT): tensile strength range from 850–1400 MPa depending on diameter and tempering temperature
Mechanical properties as per ASTM A29 / A322, EN 10083-3, or AMS specifications
AMS specifications: AMS 6359, AMS 6454, AMS 6416, AMS 6528, etc.

mechanical properties & heat treatment of 4340 steel

Heat temperature	Start forging temperature	Finish forging temperature	Cooling method
1100 – 1150 °C	1100 – 1050 °C	≥ 900 °C	Pit, sand, or furnace cooling

Annealing

Annealing temperature: 650 – 680°C.
Alternative range: 650 – 700°C.
Full annealing: 830 – 900°C, furnace cool to 300°C
Hold at temperature for sufficient time (minimum 2 hours, or 2 minutes per mm of section thickness)
Cool slowly in the furnace (slowly at approx. 15°C/h until 600°C, then air cool)
Hardness after annealing: max. 235 – 248 HB
Annealing in a protective atmosphere is recommended to reduce decarburization and surface scaling

Hardening

4340 alloy steel is typically oil quenched to achieve the required hardness. Proper preheating and austenitizing are critical to achieve the desired hardness without cracking. The steel exhibits excellent through-hardenability and can be quenched in oil, water, or polymer, depending on section size and geometry
Pre-heating (recommended): Preheat to 600 – 650°C to reduce thermal shock during austenitizing
Austenitizing temperature: 830 – 860°C.
Lower range (830–845°C): for thinner sections and complex shapes.
Upper range (845–860°C): for heavier sections requiring deeper hardness.
Alternative: 820 – 850°C
Holding time: At least 30 minutes per 25mm of section thickness (minimum 30 minutes)
Quenching media:
Oil (preferred for most sections) — provides good hardness with moderate distortion
Water — for larger sections or when faster cooling is required (increased crack risk)
Polymer — medium quench rate, good for distortion control
Hardness after quenching: 50 – 56 HRC (water quenched)

Stress relieving

Perform after rough machining, heavy stock removal, EDM, or welding to reduce residual stresses
In the annealed condition: heat to 600 – 650°C, hold for 1-2 hours, air cool
In the quenched and tempered condition: heat to 30 – 50°C below the final tempering temperature, air cool
Alternative range (general): 450 – 650°C, approximately 50°C below the tempering temperature
Hold at temperature for 1 – 2 hours (minimum)
Air cool after holding
This operation reduces the risk of distortion during final hardening and improves dimensional stability

Tempering

Temper immediately after the workpiece cools to hand-warm temperature (approx. 50–70°C). Delayed tempering may cause cracking
Number of tempers: Minimum 1 time for standard applications; 2 times recommended for critical components (e.g., aerospace) to ensure complete transformation and property stability
Holding time: 1 hour minimum at temperature per 25mm of section thickness
Cooling method: Air cool after each tempering cycle
Tempering temperature range: 540 – 680°C.
540 – 660°C: Standard tempering range
200 – 650°C: Broader range depending on final hardness requirements

Why Choose NSPM as Your 4340 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.