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9840 1.6511 SNCM439 alloy structural steel

9840 alloy structural steel offers excellent strength, deep 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 9840, DIN 1.6511(36CrNiMo4), JIS SNCM439, GB 40CrNiMoA
Technique: EAF + LF + VD, forged or hotrolled, multidirectional forging ratio ≥4, spheroidized annealed
Shape: Round, Flat, Plates, Blocks
Heat treatment: Supplied in annealed condition, hardness ≤248 HBW; quenched and tempered (QT) to 28–34 HRC 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 9840 in various custom sizes

Chemical Composition (%)

Grade	C	Si	Mn	P (≤)	S (≤)	Cr	Ni	Mo
9840	0.38–0.43	0.20–0.35	0.70–0.90	0.035	0.035	0.70–0.90	0.85–1.15	0.20–0.30
1.6511 (36CrNiMo4)	0.32–0.40	≤0.40	0.50–0.80	0.025	0.035	0.90–1.20	0.90–1.20	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 9840 alloy steel

9840 | 1.6511 | SNCM439 alloy steel applications

9840 steel for Heavy-Duty Transmission Shaft

Deep hardenability and high torsional fatigue strength enable 9840 to reliably transmit power under sustained heavy loads in mining and construction equipment.

9840 steel for Oil & Gas Drill Tool Joint

Excellent impact toughness and wear resistance withstand extreme downhole stresses and abrasive conditions, ensuring extended, trouble-free service life.

9840 steel for Aerospace Landing Gear Component

High fracture toughness and an optimal strength-to-weight ratio meet critical aerospace standards, delivering structural safety under severe landing shock loads.

Our Production Technology For 9840 (36CrNiMo4 / 1.6511 / SNCM439) High-Strength Alloy Steel

EAF
LF
VD
VIM + ESR
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 (upon agreement)
Grain size as per ASTM E112 (typical ≥ 5 for critical applications)
Delivery condition options:
Soft annealed: max. 235 HB
Normalized: refined grain structure
Quenched and tempered (+QT): mechanical properties per diameter as listed below
Mechanical properties as per ASTM A29 / A322, SAE J404, or AMS 6342
Forgings may be furnished in the following conditions: stress relieving; annealing; solution treatment; solution treatment and ageing; normalizing; normalizing and tempering; or quenching and tempering

mechanical properties & heat treatment of 9840 steel

Heat temperature	Start forging temperature	Finish forging temperature	Cooling method
1100 – 1200 °C	1150 – 1175 °C	≥ 950 – 925 °C	Pit, sand, or furnace cooling

Annealing

Hardening

9840 alloy steel can be hardened in oil or water, depending on section size, shape complexity, and quenching equipment. Proper preheating and austenitizing are critical to achieve the desired hardness without cracking
Pre-heating (recommended): Preheat to 600 – 650°C to reduce thermal shock during austenitizing
Austenitizing temperature: 830 – 865°C.
Holding time: At least 30 minutes per 25mm of section thickness
Quenching media:
Oil (preferred for thin, intricate shapes — provides good hardness with moderate distortion)
Water (for large, simple shapes — faster quench, but increases distortion and crack risk)
Polymer — medium quench rate, good for distortion control
Hardness after quenching: Dependent on section size and quenching medium

Stress relieving

Perform after rough machining, heavy stock removal, or welding to reduce residual stresses
Heat carefully to 50°C below the tempering temperature.
Alternative: 550°C after welding
Hold at temperature for 1 hour per 25mm of section thickness (minimum 2 hours)
Air cool after holding
This operation reduces the risk of distortion during final heat treatment 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 requiring maximum toughness and property stability
Holding time: 1 hour per 25mm of section thickness (minimum 2 hours)
Cooling method: Air cool after each tempering cycle
Tempering temperature range: 540 – 680°C

Why Choose NSPM as Your 9840 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.