Difference Between Carburizing and Carbonitriding

The key difference between carburizing and carbonitriding is that carburizing is the process of hardening a steel surface using carbon, whereas carbonitriding is the process of hardening a steel surface using carbon and nitrogen.

Hardening is the industrial process of increasing the hardness of a metal such as steel. Surface hardening of steel can be done in two processes: case hardening and surface hardening. Case hardening increases the hardness of the surface of the metal by infusing elements into the surface of the material, forming a thin layer of a harder alloy. In contrast, surface hardening increases the hardness of the surface, while the core remains relatively soft. Surface hardening also has two processes known as differential surface hardening and differential metal structure hardening. Carburizing and carbonitriding are the two techniques used in differential metal structure hardening process.

CONTENTS

1. Overview and Key Difference
2. What is Carburizing 
3. What is Carbonitriding
4. Side by Side Comparison – Carburizing vs Carbonitriding in Tabular Form
5. Summary

What is Carburizing?

Carburizing is the industrial process of hardening steel surfaces using carbon. In this process, the metal alloy (steel) undergoes a high-temperature treatment for several hours. Also, this treatment is done in a carbonaceous environment. Furthermore, the temperature we should use in this process should be a temperature higher than the critical temperature of steel. Here, the steel can absorb carbon into the steel surface from the carbonaceous environment and slowly diffuse into the surface layers.

Moreover, the carbonaceous environment we use in carburizing contains either charcoal or carbon monoxide. The purpose of this process is to make the surface of the steel hard and wear-resistant. Application-wise, Carburizing is suitable for mild carbon steels. Longer carburizing times increase the depth of the carbon coating. However, in this method, the surface becomes harder while the core remains soft. Some subcategories of carburizing include pack carburizing, gas carburizing, vacuum carburizing, and liquid carburizing, depending on the nature of the hardening process.

What is Carbonitriding?

Carbonitriding is an industrial technique that is useful in hardening a metal surface using carbon and nitrogen. Therefore, it is a surface modification technique. Also, this technique increases the hardness of the metal surface and reduces the wear.

Figure 01: A Furnace Used for Carbonitriding

Initially, in this carbonitriding process, carbon and nitrogen atoms diffuse into the surface of the metal. Then, the atoms create barriers to slip. Often, the carbonitriding method is inexpensive. Moreover, this technique is similar to the gas carburizing method. However, the difference is that carburizing adds only a carbonaceous environment while carbonitriding applies both a carbonaceous environment and ammonia. Here, ammonia is the source of nitrogen.

What is the Difference Between Carburizing and Carbonitriding?

Carburizing and carbonitriding are two different methods used to harden a steel surface. The key difference between carburizing and carbonitriding is that carburizing is the process of hardening a steel surface using carbon, whereas carbonitriding is the process of hardening a steel surface using carbon and nitrogen. Furthermore, Carburizing involves a carbonaceous environment, while carbonitriding involves a carbonaceous environment with ammonia gas.

Moreover, another difference between carburizing and carbonitriding is that carbonitriding is comparatively more expensive than carburizing.

Summary – Carburizing vs Carbonitriding

In brief, carburizing and carbonitriding are the two techniques used in differential metal structure hardening process. The key difference between carburizing and carbonitriding is that carburizing is the process of hardening a steel surface using carbon, whereas carbonitriding is the process of hardening a steel surface using carbon and nitrogen.

Reference:

1. Daksh Patel. “Carbonitriding.” LinkedIn SlideShare, 20 Oct. 2013, Available here.
2. “Carburization.” Carburization – an Overview | ScienceDirect Topics, Available here.
3. “Carbonitriding.” Wikipedia, Wikimedia Foundation, 9 Aug. 2018, Available here.
4. “Carburizing.” Wikipedia, Wikimedia Foundation, 19 July 2019, Available here.

Image Courtesy:

1. “Computerised Heat Treatment Furnance” By S zillayali – Own work (CC BY 3.0) via Commons Wikimedia

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