In-Depth Guide to Case Hardening Heat Treatment Carburizing, Nitriding, Carbonitriding, Nitrocarburizing

Case hardening heat treatment includes nitriding, nitrocarburizing, carburizing, and carbonitriding, a game-changer in enhancing the surface properties of metal components. This transformative process modifies the chemical composition, creating robust surface layers ranging from 0.01 to 0.25 inches deep, tailored to specific applications.

Carburizing – Most common Case Hardening Heat Treatment process to Elevate Wear Resistance for Optimal Performance

Carburization, a case hardening heat treatment, high-temperature process between 900 to 950°C, is the go-to method for parts demanding a wear-resistant surface coupled with a robust core. By diffusing carbon into the steel, carburization forms a deep wear-resistant layer, up to 0.25 inches thick. This process is particularly beneficial for gears, blades, and cutting tools, providing superior hardness to alloyed and low carbon steels like 1008, 1018, and 8620.

Table 1.  showing chemical composition of Low Carbon Steel before Carburizing Process

Table 2. Showing chemical composition of Low Carbon Steel after Carburizing Process for 180 minutes at 1050 Degree C

Carbonitriding: Enhancing Surface Hardness with Nitrogen

For lower carbon steels lacking alloying elements, carbonitriding introduces nitrogen to increase surface hardness. Operating at slightly lower temperatures (850°C) than carburizing, carbonitriding minimizes distortion while maintaining enhanced hardness and resistance to elevated temperatures. This process is ideal for alloys with microalloying elements like Cr, V, Ti, Al, and Mo, offering surface hardness ranging from 600 to 1,200 Hv. Carbonitriding is among the most preferred case hardening heat treatment in the metal industry. 

Nitriding/Nitrocarburizing: Versatile Solutions with Nitrogen

In contrast to high-temperature carburizing, nitriding/nitrocarburizing diffuses nitrogen throughout the surface layer at sub-critical temperatures (450° to 575°C). This enables processing in the final machined state with minimal distortion. Nitriding is versatile, applicable to a broad range of alloys, including stainless and tool steels rich in chromium. The resulting surface hardness can exceed 70 HRC, making it perfect for long-term wear resistance of the metal components. Nitriding or nitrocarburizing is also by major industries where case hardening heat treatment is mandatory to achieve wear resistance of up to 70HRC.

Gas Nitriding vs. Ion Nitriding: Tailoring Solutions for Diverse Needs

Gas nitriding, utilizing cracked ammonia, is suitable for large-batch processing and excels in temperature uniformity. Ion nitriding, on the other hand, allows selective nitriding, offering thinner compound zones ideal for specific applications like gears. The plasma-based process is well-suited for alloys such as stainless steels.

Nitrocarburizing: Balancing Hardness and Ductility

Nitrocarburization, performed at higher temperatures (575°C) with the addition of carbon, forms a harder, more wear-resistant layer with thicker compound zones. However, caution is warranted, as increased surface porosity and reduced ductility may impact parts with large contact stresses.

Optimizing Case Hardening Process for Your Application

Selecting the right case hardening method depends on factors like material composition, application requirements, and desired properties. While carburization is optimal for certain steels, nitriding/nitrocarburizing offers versatility across a broader alloy spectrum. Trust material experts to tailor case hardening processes, ensuring cost-effective solutions with extended wear life for your specific components. Elevate your components’ performance through the precision of case hardening.

There are also several other processes that constitute to the Case Hardening Heat Treatment Process

1. Cyaniding:

   • Cyaniding involves heating the metal part to 950 °C (1750 °F) in the presence of a cyanide-based salt to diffuse carbon and nitrogen into its surface.
   • After absorption, the part is quenched to harden it, followed by rinsing to remove cyanide residues due to its toxicity[1].

2. Carbonitriding:

   • Carbonitriding adds carbon and nitrogen to the steel surface, similar to gas carburizing but with an ammonia environment.
   • The process occurs at around 840 °C (1550 °F), between nitriding and carburizing temperatures.
   • Quenching in oil or gas follows, resulting in less distortion and achieving a hardness of up to 60 HRC[2].

3. Ferritic Nitrocarburizing:

   • Ferritic nitrocarburizing introduces carbon and nitrogen into steel while it remains in the ferritic phase.
   • This process differs from others by not heating the material above the critical temperature.
   • Types include salt bath, gaseous, and ion nitrocarburizing.

Case-hardened steel is a widely used surface treatment process in the industry world-wide. It is especially useful in applications where wear of the surface happens, shock loads, and misalignment are present. Case hardening heat treatment provides excellent hardness in these applications without increasing brittleness of the metal component.

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