FNC Heat Treatment & Carbonitriding

Introduction to Heat Treating Steel

Heat treating steel is a vital process in metallurgy that involves the use of heat to alter the physical and chemical properties of steel. This process plays a significant role in enhancing the steel’s mechanical properties such as hardness, toughness, ductility, and its resistance to wear and tear.

Steels undergo heat treatment to achieve a variety of desired properties. Some treatments make the steel softer and more ductile for shaping, while others increase its hardness for improved wear resistance. The heat treatment process involves heating the steel to a specific temperature, holding it at that temperature for a certain period, and then cooling it at a controlled rate.

There are different types of heat treatments, including hardening, tempering, annealing, normalizing, and surface hardening techniques. This article focuses on two surface hardening methods: FNC (Ferritic Nitrocarburizing) heat treatment and carbonitriding.

Understanding Hardening Heat Treatment

Hardening heat treatment is a process that increases the hardness of steel, making it more resistant to abrasion and wear. This process involves heating the steel to its austenitizing temperature, then rapidly cooling it—usually in water, oil, or air. The rapid cooling causes the steel to form martensite, a hard, brittle form of steel.

However, the hardened steel becomes too brittle for most applications. As a result, it goes through a process called tempering, which involves heating the steel to a lower temperature to reduce its brittleness while retaining most of its hardness.

Hardening heat treatment plays a significant role in a variety of industries, from automotive to construction, and contributes to the life and performance of steel parts.

What is Carbonitriding?

Carbonitriding is a type of case-hardening heat treatment that enriches the surface of steel with carbon and nitrogen. This treatment is performed at temperatures below the lower critical temperature of steel, in the presence of carbon and nitrogen-bearing gasses.

The process begins by heating the steel in a furnace filled with a carbon-rich atmosphere. Then, nitrogen is introduced into the furnace, which diffuses into the steel along with the carbon. The carbon and nitrogen diffuse into the steel’s surface, forming a hard, wear-resistant case.

Carbonitriding is often used on low-carbon steels that are not suitable for hardening. It provides a hard, wear-resistant surface while maintaining a tough and ductile core.

The Process of FNC Heat Treatment

Ferritic Nitrocarburizing (FNC) heat treatment is another case-hardening process, which enriches the surface of the steel with nitrogen and carbon. Unlike carbonitriding, FNC heat treatment is performed at temperatures below the lower critical temperature of steel, in a nitrogen-rich atmosphere.

The process begins by heating the steel in a furnace filled with a nitrogen-rich atmosphere. Then, carbon is introduced into the furnace, which diffuses into the steel along with nitrogen. The nitrogen and carbon diffuse into the steel’s surface, forming a hard, wear-resistant case.

FNC heat treatment is used to improve the wear resistance, fatigue strength, and corrosion resistance of steel parts. It is also beneficial for reducing the distortion of parts during heat treatment.

Comparing FNC Heat Treatment & Carbonitriding

Both FNC heat treatment and carbonitriding are case-hardening processes that improve the properties of steel. However, there are differences between these two processes. The main difference lies in the atmosphere used during the treatment. While carbonitriding uses a carbon-rich atmosphere, FNC heat treatment uses a nitrogen-rich atmosphere.

In terms of hardness, both processes result in similar surface hardness levels. However, FNC-treated parts typically exhibit higher fatigue strength and improved wear resistance compared to carbonitrided parts.

On the other hand, carbonitriding can achieve a greater case depth than FNC, making it more suitable for applications that require a hard, wear-resistant surface with a deeper case.

Pros and Cons of FNC Heat Treatment

FNC heat treatment offers several advantages. It improves the wear resistance, fatigue strength, and corrosion resistance of steel parts. Additionally, it reduces the distortion of parts during heat treatment, which can save costs associated with post-treatment machining.

However, FNC heat treatment also has its disadvantages. The process is more complex and requires more precise control over the furnace atmosphere and temperature. Additionally, the case depth achieved by FNC is typically less than that of carbonitriding. Therefore, FNC may not be suitable for applications that require a deeper case.

Pros and Cons of Carbonitriding

Like FNC, carbonitriding also has its pros and cons. One of the main advantages of carbonitriding is its ability to achieve a greater case depth than FNC. This makes it ideal for parts that require a hard, wear-resistant surface with a deeper case.

However, carbonitriding also has its downsides. The process can cause more distortion of parts compared to FNC, which may require additional post-treatment machining. Moreover, the process is less effective at improving corrosion resistance compared to FNC.

Applications of FNC Heat Treatment & Carbonitriding

Both FNC heat treatment and carbonitriding find extensive applications in various industries. They are used to treat parts that require improved wear resistance, fatigue strength, and corrosion resistance.

FNC heat treatment is commonly used in the automotive industry for parts such as gears, shafts, and piston rings. It’s also used in the aerospace industry for components that require high wear resistance and fatigue strength.

Carbonitriding, on the other hand, is often used for low-carbon steels that are not suitable for hardening. It is commonly used in the tool and die industry and for components like gears, shafts, and fasteners in the automotive industry.

Choosing Between FNC Heat Treatment & Carbonitriding

The choice between FNC heat treatment and carbonitriding depends on the specific requirements of the application. If the part requires a deeper case, carbonitriding may be the better choice. However, if minimizing distortion and improving corrosion resistance are more important, FNC heat treatment may be the better option.

In any case, it’s important to work with a reputable heat treatment provider that understands the unique requirements of your application and can provide the appropriate treatment.

FNC Heat Treatment & Carbonitriding

Heat treating steel is a critical process in various industries, enhancing the material’s mechanical properties to meet specific application requirements. Both FNC heat treatment and carbonitriding are valuable processes that offer unique advantages. Understanding their differences and potential applications can help businesses make informed decisions about the best heat treatment for their specific needs.

FNC Heat Treatment & Carbonitriding: 586.468.2790