18MnCr4 Cr-Mn-N Steel Round Bar

Product Description

18MnCr4 (Material Number 1.7143) is a chromium-manganese alloyed case-hardening steel (carburizing steel). While it shares the "Cr-Mn" naming convention with the previous grades you mentioned, it serves a very different purpose. Unlike the high-nitrogen austenitic steels (1.3817/1.3818), 18MnCr4 is a ferritic-pearlitic steel designed to be hardened on the surface while maintaining a tough core.

Core Specifications: 1.3818 (18MnCr4)

This grade is primarily governed by the EN 10084 standard. It is specifically engineered for components that require high surface hardness and good wear resistance, but must also withstand heavy shock loads without snapping.

Key Technical Characteristics

• Case Hardening: After carburizing (adding carbon to the surface layer), this steel achieves a surface hardness of approximately 57–62 HRC.

• Core Toughness: Because the base carbon content is low (0.18% avg), the center of the round bar remains relatively ductile after quenching, preventing brittle failure.

• Machinability: It has excellent machinability in the "as-rolled" or "annealed" condition, making it much easier to work with than the high-nitrogen austenitic grades.

• Hardenability: The combination of Mn and Cr provides better hardenability than standard carbon steels, ensuring a consistent hardened "case" depth.

Applications for Round Bars

18MnCr4 is a "workhorse" steel for mechanical engineering and automotive power transmission.

• Gears and Pinions: The most common use case; the teeth are hardened for wear, while the body stays tough.

• Shafts and Axles: Components subjected to high torsion and surface friction.

• Piston Pins: High-wear parts that require a smooth, hard exterior.

• Universal Joints: Used in drivetrains where strength and fatigue resistance are critical.

Processing & Heat Treatment

To get the most out of 18MnCr4, it typically undergoes a three-step process:

1. Carburizing: Heating the part in a carbon-rich atmosphere at 880–980°C.

2. Quenching: Rapid cooling (usually in oil) to transform the surface into martensite.

3. Tempering: Reheating at a lower temperature (150–200°C) to reduce brittleness while maintaining hardness.

International Equivalents

If you are looking for this material under different standards:

• Germany (DIN): 18MnCr4 / 1.7143

• USA (AISI/SAE): Closest to 5120 or 4820 (though not exact matches in Mn content).

• Japan (JIS): SMnC420

• France (AFNOR): 18MC4

Critical Note: Unlike 1.3817 and 1.3818, 18MnCr4 is magnetic. It does not contain the high nitrogen levels required to stabilize an austenitic structure, so it should not be used in applications requiring non-magnetic properties.