Chrome Moly 40NiCrMo7 Alloy Steel Bars

Product Description

40NiCrMo7 (often designated under European standards as 1.6562 or 40NiCrMo7-3) is an ultra-high-strength, deep-hardening Nickel-Chromium-Molybdenum low-alloy steel. Within global material specifications, 40NiCrMo7 bars serve as a premium baseline equivalent to the widely recognized North American AISI 4340 standard, but with tightly controlled European compositional parameters.

Engineered specifically for heavy-duty applications where parts face massive continuous loads, extreme torsional forces, and cryogenic shocks, this triple-alloy steel provides unmatched section-depth hardenability.

1. Chemical Formula Breakdown

The elite status of 40NiCrMo7 bars lies in its substantial Nickel ($1.60% - 2.00%$) content paired with strategic chromium and molybdenum windows:

Element	Composition (%)	Primary Metallurgical Contribution
Carbon (C)	$0.37% - 0.44%$	Provides high baseline tensile strength and deep response to quenching.
Nickel (Ni)	$1.60% - 2.00%$	Delivers massive deep-core through-hardening and exceptional low-temperature fracture toughness.
Chromium (Cr)	$0.60% - 0.90%$	Enhances surface hardness depth and improves abrasive wear resistance.
Molybdenum (Mo)	$0.15% - 0.30%$	Eliminates temper brittleness and maintains high creep resistance up to $sim 450^circtext{C}$.
Manganese (Mn)	$0.50% - 0.85%$	Functions as a fundamental deoxidizer and stabilizes phase transformations.
Silicon (Si)	$le 0.40%$	Increases the overall yield point and structural elasticity.

2. Eliminating the "Slack Quench" in Massive Cross-Sections

The primary vulnerability of standard chrome-moly steels like 42CrMo4 (AISI 4140) is their loss of core properties in thicker geometries. If a bar exceeds 80 mm in diameter, the center cannot cool fast enough during quenching, leaving a soft core.

The $Ni-Cr-Mo$ triple alloy formulation in 40NiCrMo7 delays the internal phase transformation during cooling. This allows bars up to 150 mm to 200 mm in diameter to fully transform into a uniform, high-strength martensitic structure from the outer surface straight through to the core center.

3. Mechanical Properties vs. Size (+QT Condition)

When 40NiCrMo7 bars are ordered or treated to the standard Quenched & Tempered (+QT) state (oil quenched at $820^circtext{C} - 850^circtext{C}$ and tempered at $550^circtext{C} - 650^circtext{C}$), the mechanical strength remains highly robust even as bar sizes scale:

• Small Bars ($le$ 16 mm): Ultimate Tensile Strength ($R_m$) reaches 1180 1370 MPa with a minimum Yield Strength ($R_e$) of 980 MPa.

• Medium Bars (40 mm 100 mm): Tensile strength shifts to 980 1180 MPa with a minimum yield of 780 MPa.

• Large Bars (100 mm 160 mm): Tensile strength measures 880 1080 MPa with a minimum yield of 690 MPa.

• Massive Bars (160 mm 250 mm): Maintains a highly competitive tensile strength of 830 980 MPa with a minimum yield of 640 MPa.

4. Specialized Low-Temperature Performance (ASTM A320 L43)

A distinct and critical application niche for 40NiCrMo7 is its official integration into the ASTM A320 Grade L43 specification for low-temperature bolting and fasteners.

• While standard steels turn completely brittle and fracture under subzero service, the high nickel content in 40NiCrMo7 keeps the material ductile.

• It is guaranteed to maintain a minimum impact energy of 27 Joules at a cryogenic -101C, making it standard practice for securing pressure vessels, valves, and pipelines in arctic or liquid-gas environments.

5. Main Technical Applications

Thanks to its extreme structural reliability, 40NiCrMo7 round and forged bars are machined into:

• Power & Energy Exploration: Hydroelectric turbine shafts, large drive gears, generator rotors, and high-pressure subsea couplings.

• Aerospace & Defense: Military and commercial aircraft landing gear cylinders, high-stress structural airframe pins, and propeller hubs.

• Internal Combustion: Heavy-duty marine or locomotive engine crankshafts, connecting rods, and camshafts.

6. Seamless Global Cross-References

If you are translating international engineering blueprints or evaluating factory Mill Test Certificates (MTCs), 40NiCrMo7 aligns with these premium global grades:

• USA: AISI 4340 / SAE 4340 / UNS G43400 / ASTM A320 L43

• Germany / Europe: DIN 1.6562 / 40NiCrMo8-4 (and close sister 1.6582 / 34CrNiMo6)

• United Kingdom: BS 817M40 (Classic EN24 / EN24A)

• Japan: JIS SNCM439

• Russia: GOST 40KhN2MA (402)

• China: GB 40CrNiMoA

7. Machining & Fabrication Reality

  Technical Sourcing Notes

• Machinability: In its fully hardened (+QT) structural state, it sits at roughly 320 HBW ($sim$34 HRC) and requires rigid CNC setups and high-quality carbide tooling. For elaborate gear cutting or deep gundrilling, it is highly recommended to source the bars in the Soft Annealed (+A) condition ($le$ 269 HBW) and heat-treat post-machining.

• Welding Sensitivity: Due to its exceptional hardenability and high carbon equivalent, 40NiCrMo7 is highly sensitive to cold cracking. Structural welding is generally prohibited. If welding must be performed for component repair, mandatory preheating to $300^circtext{C}$, low-hydrogen consumables, and an immediate Post-Weld Heat Treatment (PWHT) are absolute requirements to protect the heat-affected zone (HAZ).

Superior Mechanical Properties for Demanding Applications

The 40NiCrMo7 alloy steel bars boast outstanding mechanical performance, including a minimum yield strength of 850 MPa and tensile strength above 1100 MPa, depending on the heat treatment. This makes them highly dependable for critical engineering and heavy-duty operations, ensuring reliability and safety even under strenuous conditions.


Customized Dimensions and Finishes

With diameters from 16mm to 250mm and lengths between 2 and 6 meters, these bars can be tailored to precise industrial specifications. Finishes such as bright, black, and peeled are available, along with various tolerance levels (H9, H11, K12), ensuring each product fits unique operational needs with consistent quality.


Versatile Manufacturing and Supply Solutions

As a comprehensive dealer, manufacturer, exporter, and supplier based in India, we offer Chrome Moly 40NiCrMo7 alloy steel bars for a variety of sectors. End protection options such as plastic caps or painted ends ensure quality on delivery, while strict adherence to international standards guarantees performance and compliance.