20Cr2Ni4A Alloy Steel: Properties and Applications

20Cr2Ni4A Alloy Steel is a versatile low-carbon, high-alloy case-hardening steel known for its excellent combination of surface hardness and core toughness after appropriate heat treatment. Understanding its technical characteristics is essential for leveraging its full potential in demanding applications.

1. 20Cr2Ni4A Alloy Steel Chemical Composition (GB/T 3077—1999)

The typical chemical composition (mass fraction, %) for 20Cr2Ni4A is:

Elemento	Carbono (C)	Silicio (Si)	Manganeso (Mn)	Cromo (Cr)	Níquel (Ni)	Fósforo (P)	Azufre (S)	Cobre (Cu)
Min %	0.17	0.17	0.3	1.25	3.25	0	0	0
Max %	0.23	0.37	0.6	1.65	3.65	0.025	0.025	0.3

The low carbon content designates this as a case-hardening steel. The significant chromium and high nickel content enhance hardenability, allowing for effective hardening even in larger sections, while also contributing to strength and toughness.

2. 20Cr2Ni4A Alloy Steel Equivalents

20Cr2Ni4A is specified under the Chinese standard GB/T 3077—1999. Comparable international grades include:

• AISI (USA):E3316
• DIN (Alemania):22NiCr14 (or 1.5752)
• JIS (Japón):SNCM420 (or 20NC14)
• AFNOR (France):20NCD7 (or 659)
• Licenciatura (Reino Unido):659M15 (or EN A15)
• GOST (Rusia):20Х2Н4А

While these grades are similar, slight variations in specified chemical composition ranges may exist.

3. Key Physical Properties and Heat Treatment Guidance

3.1 Temperaturas críticas

Understanding the critical transformation temperatures is vital for effective heat treatment:

• Ac1:~705°C – 720°C
• Ac3:~775°C – 780°C
• EM:~305°C – 395°C (depending on exact composition)

(Note: Ar1 and Ar3 temperatures related to cooling transformations are also important but often derived or specified in detailed heat treatment protocols).

3.2 20Cr2Ni4A Alloy Steel Tratamiento térmico

Achieving the desired properties in 20Cr2Ni4A requires precise heat treatment control:

• Forja:Heat to 1150°C – 1200°C. Start forging between 1120°C – 1180°C, finish above 850°C. Slow cooling followed by annealing or tempering is recommended.
• Recocido:Heat to 810°C – 870°C, followed by furnace cooling. This achieves optimal machinability (≤217 HBW).
• Carburizing:Typically performed at austenitizing temperatures (e.g., 900°C – 950°C) to diffuse carbon into the surface. Case depth (0.2 mm to 1.5 mm) and surface carbon content (0.7% – 1.0%) depend on the application. Vacuum carburizing is also an option.
• Temple:Essential after carburizing to achieve high surface hardness (martensite). Usually involves oil quenching directly from carburizing temperature or after reheating (e.g., 860°C – 880°C or 780°C – 860°C depending on the process).
• Templado:Low-temperature tempering (150°C – 200°C) after quenching is crucial to relieve stress and reduce brittleness while maintaining surface hardness. Careful control is needed to avoid temper brittleness.
• Sub-zero Treatment (Optional):Can be applied after quenching (-60°C to -80°C) to minimize retained austenite and further increase surface hardness before final tempering.

4. 20Cr2Ni4A Alloy Steel Aplicaciones

20Cr2Ni4A steel is selected for components requiring high surface wear resistance combined with excellent core strength and toughness:

• Moldes de plástico:Suitable for large and medium-sized molds, especially those with complex cavities or used with abrasive plastics (e.g., containing fillers). Its good hardenability ensures sufficient hardness in larger sections.
• Gears and Shafts:Ideal for heavily loaded gears, pinions, worms, crankshafts, and spline shafts in automotive, locomotive, and general machinery applications.
• Bearings:Used for manufacturing large, impact-resistant roller bearings (races and rollers) for heavy machinery (rolling mills, mining equipment).
• Other Carburized Components:Axles, sleeves, clutches, machine tool spindles, piston pins, and universal joint crosses subjected to heavy loads and impact stress.

5. Specific Considerations for Mold Making

• Formabilidad:In the annealed state, the steel has good plasticity, allowing for cold forming of cavities.
• Case Depth:Molds for abrasive plastics generally require deeper carburized cases (1.3-1.5 mm) compared to those for softer plastics (0.8-1.2 mm).
• Austenita retenida:High-temperature tempering before the final quench can help reduce retained austenite.
• Control de calidad:Careful management during steel production and heat treatment is necessary to mitigate risks like white spots and temper brittleness.

6. Resumen

20Cr2Ni4A is a high-performance case-hardening alloy steel offering superior hardenability and an excellent balance of surface hardness and core toughness. It is a primary choice for demanding applications in plastic molding, heavy-duty gearing, bearings, and other critical mechanical components. Achieving optimal performance relies on precisely controlled heat treatment tailored to the specific application requirements.