AISI 4340 36CrNiMo4 1.6511 SNCM439 EN24 Alloy Steel

Product Overview

DIN 36CrNiMo4 (1.6511) is a core grade of European standard high-strength alloy steel, belongs to the European standard EN 10083-3 and EN 10250-3, and AISI 4340 is its American standard equivalent. Both belong to the low-alloy high-strength steel system with Cr-Ni-Mo as the main alloying elements, with carbon content controlled in the range of 0.32%~0.43%. After quenching and tempering (QT) heat treatment, the steel forms a tempered sorbite structure, which achieves a perfect balance of high tensile strength, excellent toughness, good fatigue resistance and wear resistance.

It is widely used in various industries, including heavy machinery, automotive, aerospace, and energy sectors, due to its excellent mechanical properties. You can find its equivalent steel grades in different country standards, such as ASTM 4340 from the American standard ASTM A29/A29M, SNCM439/SNCM8 from the Japanese standard JIS G4105, 40CrNi2MoA from the Chinese standard GB/T 3077, and 817M40/EN 24 from the British standard BS 970.

Different from ordinary carbon steel and low-alloy steel, this grade has superior through-hardening performance, and can maintain uniform hardness and mechanical properties even for large-section workpieces (up to 660mm in diameter), which solves the problem of performance attenuation of large forgings in the core area. It is known as a "high-grade quenched and tempered steel" in the industry, and is the first choice for manufacturing key load-bearing components with high reliability requirements.

International Equivalent Grades

The chemical composition and mechanical properties of this series of steel grades are highly consistent in major international standards, and can be interchanged for most applications. The detailed equivalent comparison is as follows:

Country	USA	Europe	China	British	Japan
Standard	ASTM A29	EN10083-3	GB/T3077	BS970	JIS G4105
Grade	4340	36CrNiMo4/1.6511	40CrNi2MoA	817M40/EN24	SNCM439/SNCM8

Product Features

Chemical Composition

The chemical composition of AISI 4340 is strictly controlled by Hunan Qilu Steel, with the impurity content (P/S) lower than the national standard limit, ensuring the stability of mechanical properties of each batch of products. The reasonable matching of Cr, Ni and Mo elements not only improves the hardenability and strength of the steel, but also avoids the reduction of toughness caused by excessive alloying. The detailed composition range is as follows:

Grade	C	Si	Mn	P	S	Cr	Mo	Ni
4340	0.38-0.43	0.15-0.35	0.60-0.80	0.035Max	0.040Max	0.70-0.90	0.20-0.30	1.65-2.00
36CrNiMo4/1.6511	0.32-0.40	0.4Max	0.50-0.80	0.035Max	0.035Max	0.90-1.20	0.15-0.30	0.90-1.20
40CrNi2MoA	0.38-0.43	0.17-0.37	0.60-0.80	0.030Max	0.030Max	0.70-0.90	0.20-0.30	1.65-2.00
EN24	0.35-0.45	0.10-0.35	0.45-0.70	0.050Max	0.050Max	0.90-1.40	0.20-0.35	1.30-1.80
SNCM439	0.36-0.43	0.15-0.35	0.60-0.90	0.030Max	0.030Max	0.60-1.00	0.15-0.30	1.60-2.00

Mechanical Properties After Quenching and Tempering

The mechanical properties of DIN 36CrNiMo4 are closely related to the section size of the workpiece. Hunan Qilu Steel strictly follows the EN 10250-3 standard to test the mechanical properties of open-die forgings, and the test samples are taken in accordance with EN 10250-1 (4/T below the heat treatment surface, t/2 from the end). The minimum mechanical properties of different section sizes after QT treatment (quenching 820~860℃, tempering 540~680℃) are as follows:

Size range	Tensile strength	Yield strength	Alongation		Impact value at RT/J
			L	Tr	L	Tr
d≤160	750Mpa Min	550Mpa Min	14% Min	10% Min	45J Min	22J Min
160＜d≤330	700Mpa Min	500Mpa Min	15% Min	11% Min	45J Min	22J Min
330＜d≤660	650Mpa Min	450Mpa Min	16% Min	12% Min	40J Min	20J Min

Remark: L= Longitudinal    Tr = Transverse

Key Feature: The transverse mechanical properties of the steel are excellent (elongation ≥10%, impact value ≥20J), which is suitable for manufacturing components subjected to complex multi-directional loads (such as crankshafts, gear shafts, crane hooks), avoiding brittle fracture caused by transverse stress concentration.

Hardenability and Surface Hardness Control

Surface Hardness of Different Heat Treatment Processes

DIN 36CrNiMo4 1.6511 can be adjusted for surface hardness through different heat treatment processes to meet the requirements of different application scenarios, from easy machining to high wear resistance. The hardness range is as follows:

Heat Treatment	Hardness
Flame or Induction hardening	54-62HRC
Treated to improve shearability (+S)	HB250Max
Soft annealed (+A)	HB217Max
Quenched and tempred (+QT)	HRC28-32(Common Range)

Graded Hardenability Options

For customers with controlled hardenability requirements, we provide three customized grades (+H/+HH/+HL), and the hardness distribution at different distances from the quenched end is strictly in accordance with the standard, ensuring the consistency of heat treatment effect of batch workpieces. The key hardenability values (HRC) are as follows:

Distance in mm from quenched end
Distance		1.5	3	5	7	9	11	13	15	20	25	30	35	40	45	50
Hardness In HRC + H	max	59	59	58	58	57	57	57	56	55	54	53	52	51	50	49
	min	51	50	49	49	48	47	46	45	43	41	39	38	36	34	33
Hardness In HRC + HH	max	59	59	58	58	57	57	57	56	55	54	53	52	51	50	49
	min	54	53	52	52	51	50	50	49	47	45	44	43	41	39	38
Hardness In HRC + HL	max	56	56	55	55	54	54	53	52	51	50	48	47	46	45	44
	min	51	50	49	49	48	47	46	45	43	41	39	38	36	34	33

Core Advantage: The high hardenability of the steel ensures that even large-section forgings (e.g., 660mm diameter wind turbine main shafts) can achieve uniform hardness from the surface to the core, avoiding performance defects such as soft core.

Scatter bands for the Rockwell - C hardness in the end quench hardenability test.

Supply Specifications, Tolerance and Surface Finish

Hunan Qilu Steel provides DIN 36CrNiMo4 1.6511 in multiple product forms, with strict dimensional tolerance and straightness control, reducing the post-processing time and cost of customers. The supply specifications are as follows:

Product type	Size range	Length
Hot rolled bar	Φ16-Φ310mm	6000-9000mm
Hot forged bar	Φ100-Φ1200mm	3000-5800mm
Hot rolled plate/sheet	T:3-200mm; W:1500-2500mm	2000-5800mm
Hot Forged block	T: 80-800mm; W: 100-2500mm	2000-5800mm

Straightness Guarantee

• Precision finished products (turned/milled/peeled bars): ≤1mm/1000mm

• Unfinished products (black rolled/forged): ≤3mm/1000mm

Surface Finish	Turned	Milled	Grinding(Best)	Polished(Best)	Peeled(Best)	Black Forged	Black Rolled
Tolerance	+0/+3mm	+0/+3mm	+0/+0.05mm	+0/+0.05mm	+0/+0.1mm	+0/+5mm	+0/+1mm
Straighness	1mm/1000mm max.					3mm/1000mm max.

In-Stock Sizes

We maintain monthly stock of 10,000+ tons to support quick delivery. The common in-stock sizes of hot rolled bars are Φ18,20,22,25,28,30,32,35,40,45,50~240mm; forged bars are Φ100,120,150,200~1200mm; plates are 10,15,20,25~200mm thick.

Typical Application Fields

DIN 36CrNiMo4 1.6511 is widely used in high-end manufacturing fields due to its excellent comprehensive properties, and is the core material for manufacturing key components with high load, high speed and high reliability requirements. The detailed application scenarios are as follows:

1. Heavy Machinery Manufacturing

As the "backbone material" of heavy machinery, it is used for manufacturing core components subjected to high loads and cyclic impacts:

• Transmission systems: Gears, drive shafts, differential components of excavators, bulldozers and cranes (tensile strength ≥700MPa resists tooth wear and shaft bending)

• Power transmission: Crankshafts and connecting rods of diesel engines for mining trucks and agricultural machinery (excellent fatigue resistance ensures long service life under repeated load cycles)

• Structural fasteners: High-strength bolts and nuts for heavy frame assembly (QT hardness 28~32HRC prevents loosening under vibration)

2. Aerospace and Defense

Complies with strict aviation standards (e.g., AMS 6414, ASTM F2881), and is the core material for aerospace and defense equipment:

• Engine parts: Turbine shafts and compressor disks (high-temperature stability up to 300℃ and creep resistance maintain performance under high-speed operation)

• Defense equipment: Armor plates and missile components (induction hardening up to 62HRC for excellent ballistic protection and impact resistance)

3. Automotive Industry

Suitable for high-performance cars and heavy-duty commercial vehicles, with excellent durability under extreme torque and temperature:

• Transmission gears: Manual/automatic gearbox gears of sports cars and heavy trucks (wear resistance 30% higher than 4140 steel after hardening)

• Chassis components: Drive shafts and suspension links of heavy-duty trucks (yield strength ≥500MPa resists deformation under heavy payloads)

• Performance engines: Camshafts and piston rods of racing engines (low carbon equivalent CE ≤0.65 minimizes high-speed cracking)

4. Energy Sector

Adapt to harsh working environments of renewable energy and traditional energy, and is the first choice for key components of energy equipment:

• Wind energy: Main shafts and gearbox internals of onshore/offshore wind turbines (fatigue resistance of 10^7 cycles at 60% tensile strength, service life ≥20 years)

• Oil & Gas: Drilling collars and downhole tools for deep-well exploration (Cr/Mo elements improve corrosion resistance, tensile strength ≥650MPa withstands high pressure and abrasive fluids)

• Power generation: Turbine shafts of thermal power plants (heat resistance up to 350℃ after tempering, stable performance in high-temperature steam)

5. Mold and Tool Manufacturing

Ideal for manufacturing molds requiring both high strength and wear resistance:

• Stamping dies: Blanking and forming dies for metal sheets (surface hardness 54~62HRC resists galling, die life 50% higher than mild steel)

• Forging dies: Hot forging dies for aluminum and steel components (impact value ≥40J prevents cracking under repeated hammer strikes)

Comparison with Common Similar Grades

Customers often confuse AISI 4340/DIN 36CrNiMo4 1.6511 with 4140/42CrMo, 4330 and other grades. The following is a detailed comparison of core differences in composition, performance and application, to help customers select the most suitable material:

1. AISI 4340 vs AISI 4140 (42CrMo)

The most common comparison combination, the core difference lies in the addition of Ni element in 4340, which leads to a huge gap in toughness and hardenability:

Index	AISI 4340 (36CrNiMo4)	AISI 4140 (42CrMo)	Key Selection Suggestion
Alloy Elements	Contain Ni (1.65-2.00%), Cr-Mo co-alloying	No Ni, only Cr-Mo alloying	4340 is suitable for low-temperature and high-toughness requirements; 4140 is for general load-bearing
Tensile Strength	≥750MPa (d≤160mm)	≥650MPa (d≤160mm)	4340 has 15% higher strength for the same section
Impact Toughness	≥45J (RT)	≥30J (RT)	4340 is more suitable for components subjected to impact loads (e.g., crane hooks)
Hardenability	Excellent, through-hardening for d≤660mm	General, through-hardening for d≤200mm	4340 is the only choice for large-section forgings
Application	High-end key components (aerospace, wind turbine shafts)	General mechanical components (ordinary shafts, bolts)	Choose 4140 for cost control; 4340 for high reliability

2. AISI 4340 vs AISI 4330

Same series of Cr-Ni-Mo steel, the difference is in carbon and Ni content, leading to different strength-toughness balance:

• AISI 4330: C (0.28~0.33%), Ni (1.65~2.00%), lower strength (≥650MPa) but better low-temperature toughness (≥60J at -40℃)

• AISI 4340: Higher C content, higher strength but slightly reduced low-temperature toughness

Selection: 4330 for low-temperature working conditions (e.g., polar engineering machinery); 4340 for normal temperature high-load conditions

3. DIN 36CrNiMo4 vs 40CrNi2MoA

Chinese standard 40CrNi2MoA is a direct equivalent of AISI 4340, with slightly different from DIN 36CrNiMo4:

• 40CrNi2MoA: Strict P/S control (≤0.030%), higher purity, suitable for high-precision components

• 36CrNiMo4: Lower Ni content (0.90~1.20%), lower cost, suitable for European standard matching projects

Selection: 40CrNi2MoA for domestic high-precision manufacturing; 36CrNiMo4 for export projects matching European standards

FAQ

Q1: What heat treatment processes are recommended for AISI 4340/DIN 36CrNiMo4 1.6511?

A1: The performance of the steel is optimized through three core heat treatment processes, which are tailored to different processing stages:

• Soft Annealing (+A): Heat to 650~700℃, hold for 2~4h (depending on section size), furnace cooling. Hardness ≤217HB, easy for rough machining.

• Normalization (+N): Heat to 850~880℃, hold for 1~2h, air cooling. Refine grain structure, improve uniformity, and prepare for QT treatment of large forgings.

• Quenching & Tempering (QT): The core process for achieving high performance. Heat to 820~860℃ (low for water quenching, high for oil quenching), hold until full austenitization, quench in water/oil, then temper at 540~680℃ for 1~3h, air cooling. Obtain high strength (≥750MPa) and toughness (≥45J) balance.

Q2: Is AISI 4340/DIN 36CrNiMo4 1.6511 weldable? What are the key welding points?

A2: The steel is technically weldable but has poor weldability (C content 0.32%~0.43% > 0.25% threshold, high risk of weld cracking). The key welding process requirements to ensure welding quality are as follows:

• Preheating: Preheat the base material to 200~300℃ to reduce thermal stress and avoid cold cracking.

• Welding consumables: Use low-hydrogen consumables (e.g., E11018-G for SMAW, ER110S-G for GMAW) to minimize hydrogen-induced cracking.

• Post-weld heat treatment (PWHT): Temper at 600~650℃ for 1~2h after welding, slow cooling to relieve residual stress and restore ductility.

• Prohibition: Avoid welding thick sections (>50mm) without preheating.

Q3: What are the mechanical properties of a 200mm-diameter DIN 36CrNiMo4 forging after QT treatment?

A3: 200mm diameter belongs to the range of 160mm ＜ d ≤ 330mm, and the minimum mechanical properties after QT treatment (per EN 10250-3) are:

• Tensile Strength: ≥700MPa

• Yield Strength: ≥500MPa

• Elongation: Longitudinal ≥15%, Transverse ≥11%

• Impact Value (RT): Longitudinal ≥45J, Transverse ≥22J

• Hardness: 28~32HRC (adjustable via tempering temperature)

• Application: Suitable for mid-size key components such as gear shafts, crane hooks, wind turbine intermediate shafts.

Q4: How to ensure the quality of AISI 4340/DIN 36CrNiMo4 1.6511 products?

A4: Hunan Qilu Steel implements full-process quality control from raw material smelting to finished product delivery:

• Smelting: Adopt electric arc furnace + LF/VD refining process, control P/S ≤0.035%, ensure low gas content (H ≤2ppm, O ≤20ppm).

• Forging/Rolling: Adopt large-tonnage forging equipment, ensure sufficient deformation ratio (≥3:1), refine grain.

• Heat Treatment: Use professional controlled atmosphere heat treatment furnace, ensure uniform heating and cooling, avoid oxidation and decarburization.

• Testing: 100% ultrasonic flaw detection (UT) in accordance with EN 10246, mechanical property testing, chemical composition analysis, and provide a complete quality inspection report.

Q5: Can customized heat treatment and processing services be provided?

A5: Yes. We provide one-stop customization services according to customer requirements:

• Custom heat treatment: Adjust tempering temperature to achieve the required hardness (25~35HRC) and mechanical properties.

• Precision processing: Turning, milling, drilling, grinding, etc., to meet the dimensional tolerance requirements of finished components.

• Surface treatment: Shot blasting, phosphating, painting, etc., to improve corrosion resistance.

• Custom forgings: According to customer drawings, manufacture non-standard large forgings with diameter up to 1200mm.

Inquire Now: We will reply to your inquiry within 24 hours and provide professional material selection suggestions and quotation services according to your application scenarios and technical requirements!