Main Difference – Carburizing vs Nitriding
Heat treatment is the use of heat to modify the properties of a material, especially in metallurgy. Heat treatment is done via heating and cooling of substances. It is used to alter one or more chemical and physical properties in order to obtain desirable properties such as increased strength, increased hardness, resistance to impact, softening, and increase ductility. There are four major types of heat treatment methods as annealing, tempering, hardening, and normalizing. Hardening is the process of increasing the hardness of a metal. There are two major types of hardening processes as case hardening and surface hardening. Surface hardening can be done in two processes known as differential surface hardening and differential metal structure hardening. Carburizing and Nitriding are the two techniques used in differential metal structure hardening process. The main difference between carburizing and Nitriding is that in carburizing, carbon is diffused to the steel surface whereas, in Nitriding process, nitrogen is diffused to the steel surface.
Key Areas Covered
1. What is Carburizing
– Definition, Different Types
2. What is Nitriding
– Definition, Improvement of Properties
3. What is the Difference Between Carburizing and Nitriding
– Comparison of Key Differences
Key Terms: Annealing, Carburizing, Case Hardening, Gas Carburizing, Hardening, Liquid Carburizing, Metallurgy, Nitriding, Pack Carburizing, Surface Hardening, Tempering, Vacuum Carburizing
What is Carburizing
In carburizing, the metal alloy is placed at a high temperature for several hours in a carbonaceous environment. The temperature should be higher than metal’s upper transformation temperature (critical temperature). Then, carbon is absorbed into steel from the carbonaceous environment and slowly diffused into the surface layers.
The carbonaceous environment can be charcoal or carbon monoxide. The purpose of carburizing is to make the surface of the steel hard and wear resistant. This technique is mainly used 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.
There are four main forms of carburizing as follows.
Pack Carburizing
Here, components are packed in an environment with a high carbon content. Components are heated with the production of carbon monoxide (a reducing agent). The reduction by carbon monoxide occurs on the steel surface with the release of carbon that is diffused into the surface due to high temperatures. Then this carbon gets hardened.
Gas Carburizing
Here, carbon monoxide is supplied to the heated furnace. Rest of the process is similar to that of gas carburizing.
Vacuum Carburizing
This process involves the carburizing of steel in an oxygen-free, low-pressure Since the system is oxygen-free, the temperature can be considerably increased without any surface oxidation. Higher temperatures increase the carbon diffusion rates and thus the hardening is increased.
Liquid Carburizing
Here, the steel is submerged in a liquefied carbon environment. Carbon diffusion is more efficient in this method.
What is Nitriding
Nitriding is a heat-treating process that diffuses nitrogen into the surface of a metal to create a hardened surface. The Nitriding process utilizes nitrogen and heat. This is usually used for fuel injection pumps. In this method, nitrogen is diffused to the steel surface instead of carbon. Nitriding can be done at lower temperatures than carburizing.
Figure 1: A Computerized Heat Nitriding Treatment Furnace
The diffusion of nitrogen gas normally occurs at low temperatures, and hardening occurs without quenching. Only the surface is hardened, the core remains the same. When a steel has undergone Nitriding process, it has excellent wear resistance. The corrosion resistance is also improved. In addition, the fatigue life of steel is improved. Fatigue property is the capacity of steel to withstand a stress without breakage.
Difference Between Carburizing and Nitriding
Definition
Carburizing: Carburizing is a heat treatment process that diffuses carbon into the surface of a metal to create a hardened surface.
Nitriding: Nitriding is a heat-treating process that diffuses nitrogen into the surface of a metal to create a hardened surface.
Components
Carburizing: Carburizing uses a carbonaceous environment.
Nitriding: Nitriding uses nitrogen instead of carbon.
Temperature
Carburizing: Carburizing is done at very high temperatures.
Nitriding: Nitriding can be done at low temperatures.
Diffusion
Carburizing: In carburizing, carbon is diffused onto the surface of the metal alloy.
Nitriding: In Nitriding, nitrogen is diffused onto the surface of the metal alloy.
Conclusion
Carburizing and Nitriding are two types of surface hardening processes that are used to make a steel surface hardened while the core remains soft. The main difference between carburizing and Nitriding is that in carburizing, carbon is diffused to the steel surface whereas, in Nitriding process, nitrogen is diffused to the steel surface.
Reference:
1. “Carburizing Process and Techniques – Four Methods of Carburizing.” Brighthub Engineering, 25 May 2011, Available here.
2. “What is Nitriding? – Definition from Corrosionpedia.” Corrosionpedia, Available here.
3. “Nitriding.” Wikipedia, Wikimedia Foundation, 12 Jan. 2018, 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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