W.Nr. 20NiCrMo2 Alloy Steel Chrome Moly Bars

Product Description

W.Nr. 1.6523 (standardized as 20NiCrMo2-2 or simply 20NiCrMo2 under EN 10084) is a highly prominent Nickel-Chromium-Molybdenum low-alloy steel. While it contains chromium and molybdenum, it belongs firmly to the triple-alloy case-hardening (cementation) steel family.

If you are sourcing or machining W.Nr. 20NiCrMo2 bars, you are using the precise European equivalent to the globally standard North American AISI 8620 grade. It is specifically formulated for components that require an incredibly hard outer protective shell to resist severe friction, while retaining a highly ductile, shatter-proof inner core to absorb impact.

1. Chemical Formula (EN 10084)

The intentional reduction of base carbon combined with small, synergistic additions of Nickel, Chromium, and Molybdenum defines its unique microstructure:

Element	Composition (%)	Primary Metallurgical Role
Carbon (C)	$0.17% - 0.23%$	Kept deliberately low to ensure the core remains weldable and highly ductile after quenching.
Nickel (Ni)	$0.40% - 0.70%$	Increases internal core toughness, impact strength, and fatigue resistance.
Chromium (Cr)	$0.35% - 0.70%$	Enhances hardenability depth and permits excellent surface hardness during carburizing.
Molybdenum (Mo)	$0.15% - 0.25%$	Refines grain structure and protects against temper brittleness.
Manganese (Mn)	$0.65% - 0.95%$	Stabilizes heat treatment response and acts as a deoxidizer.

2. The Case-Hardening Strategy

Because the base carbon of a 20NiCrMo2 bar sits at only $sim0.20%$, standard direct quenching will not yield high surface hardness. Instead, machined components are put through a carburizing cycle:

1. Carburizing ($880^circtext{C} - 980^circtext{C}$): The part is heated in a carbon-rich atmosphere, forcing carbon to diffuse into the surface layer up to a depth of 0.5 to 2.0 mm, raising the outer carbon concentration to $sim0.80%$.

2. Quenching ($780^circtext{C} - 820^circtext{C}$): The bar is rapidly cooled in oil or water.

3. Tempering ($150^circtext{C} - 200^circtext{C}$): A low-temperature bake relieves internal stresses.

• The Final Dual-State Result: You achieve a glass-hard surface case of 58 to 63 HRC for supreme wear resistance, wrapped around a strong, resilient inner core with a core tensile strength of 700 to 1100 MPa (depending on bar cross-section diameter).

3. Core Delivery & Structural Conditions

When purchasing W.Nr. 20NiCrMo2 bars from a service center, they are usually supplied in specific structural conditions:

• Soft Annealed (+A): Normalized/annealed to a maximum hardness of 212 HBW. This is the standard choice for precision CNC machining, turning, and gear-cutting to extend tool insert life.

• Treated to Ferrite-Pearlite Structure (+FP): Controlled cooled to a predictable hardness window (149 to 194 HBW) optimized specifically for consistent high-speed machining and dimensional stability.

• Treated for Cold Shearability (+S): Softened to a max of 255 HBW to allow heavy industrial cold shears to chop or cold-head the bar stock without cracking the outer edges.

4. Key Engineering Applications

20NiCrMo2 bars are frequently machined into components exposed to severe contact friction and violent torque shifts:

• Automotive & Powertrain: Driving bevel gears, planetary gear sets, crown wheels, splined transmission shafts, and camshafts.

• Mechanical Components: Heavy-duty bushings, sleeves, high-load guide pins, link pins, and universal joint journals.

• Industrial Fasteners: Specialized structural fasteners and high-fatigue bolts subject to intense shearing loads.

5. Direct Global Cross-References

If you are interpreting global technical prints or trying to verify mill test certificates (MTCs):

• USA: AISI 8620 / SAE 8620 / UNS G86200

• Japan: JIS SNCM220 / SNCM220H

• France (AFNOR): 20NCD2 / 22NCD2

• United Kingdom: BS 805M20 / 806M20

• China: GB 20CrNiMo

• Russia: GOST 20KhNM (20)

6. Machining & Welding Guidelines

  Fabrication Notes

• Excellent Machinability: In the supplied +A or +FP conditions, this material machines cleanly and leaves an exceptionally smooth surface finish, which is ideal for the tight tolerances required by gearboxes.

• Favorable Weldability: Thanks to its low base carbon content, 20NiCrMo2 features significantly better weldability than high-carbon chrome-moly grades like 42CrMo4 (AISI 4140). However, because of the nickel and chromium content, preheating the bar to $150^circtext{C} - 200^circtext{C}$ is still highly recommended for thicker cross-sections to eliminate any risk of hydrogen micro-cracking in the heat-affected zone (HAZ).

Superior Alloy Composition for Enhanced Performance

20NiCrMo2 Alloy Steel Bars are designed with a unique blend of Nickel, Chromium, and Molybdenum, providing excellent toughness, strength, and wear resistance. These properties make the bars particularly suitable for case-hardening, nitriding, and carburizing processes, which are essential for producing durable components for automotive and industrial machinery.


Versatile Surface and Delivery Conditions

Customers can choose from a variety of surface conditions, including bright, black, polished, peeled, and turned finishes, as well as delivery states like annealed or as rolled. This flexibility allows for optimized performance and easier processing during manufacturing, with each bar marked for traceability and supplied in secure bundles.


Customizable Dimensions to Suit Every Requirement

With diameters ranging from 20 mm to 350 mm and customizable lengths, 20NiCrMo2 Alloy Steel Bars can be tailored to the specific needs of various industries. Whether for gears, shafts, or structural machinery, these bars provide the dimensional accuracy and reliability required for precision engineering applications.