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Ferritic Nitrocarburizing (FNC)/Salt Bath Nitriding

January 17th, 2021

Firearm, automobile, aerospace and other manufacturing industries use case-hardening techniques to improve their products durability, corrosion resistance and other features. As an affordable and effective case-hardening technique, ferritic nitrocarburizing/salt bath nitriding offers distinct advantages. Learn more about liquid nitriding and how Specialty Steel Treating can improve the critical qualities of your manufactured components.

History of Ferritic Nitrocarburizing

Ferritic nitrocarburizing, known as FNC or salt bath nitriding, started to be used in the 1950s. This process was introduced to solve the issues with low-temperature salt bath processing being used in Great Britain. This older treatment option was water soluble, so it could be washed off during routine cutting tool cleaning.

Liquid nitriding further improved the gaseous process. Instead of just introducing nitrogen, like typical nitriding services, FNC introduces nitrogen and carbon. The process has continued to be refined and performed using state-of-the-art equipment to deliver impressive case hardening results.

How the FNC Process Works

FNC starts by heating the steel component to a precise temperature. It uses a salt bath for liquid nitriding. As the workpiece is heated, it becomes diffused with both carbon and nitrogen atoms. The temperature range is usually lower than other heat treatment levels to reduce the risk of distortion.

Finally, the component is quenched at a precise temperature and rate to control the cooling process. This ensures the nitrogen, carbon and oxygen atoms are locked into the iron in the ideal arrangement. Failure to handle the quenching process properly can affect the entire case-hardening process.

This process is commonly used to create hydraulic components, transmission components and other durable steel parts. Many materials can be processed using FNC, including these common options:

  • High alloy steels
  • Low alloy steels
  • Unalloyed steels
  • Stainless steels
  • Ductile iron
  • Cast iron
  • Sintered metals

Benefits of Ferritic Nitrocarburizing/Salt Bath Nitriding

Choose liquid nitriding from Specialty Steel Treating for a number of benefits to your final product. Here are just a few reasons that manufacturers from diverse industries choose this process:

  • Increased durability: High wear resistance levels ensure your hydraulic shafts, axle components and other manufactured products can withstand extreme pressure and wear during normal operation.
  • Reduced part weight: A durable exterior allows engineers to create components using altered specifications. The result can be a lighter component that offers the same level of wear resistance.
  • Improved corrosion resistance: Cast iron, steel and sintered metals can all enjoy higher levels of corrosion resistance after undergoing the FNC case hardening process.

The overall process is an efficient way to improve the dependability of your automotive, hydraulic or firearm components. Whether you’re creating a complete product or sending custom components to a manufacturer, consider FNC as an alternative to other case hardening processes.

Limitations of the FNC Process

The FNC process is not for every workpiece. While liquid nitriding can improve the durability, corrosion resistance and lightweight features of your manufactured components, there are a few reasons to consider a different case hardening process. Here are some limitations of the FNC process:

  • Reduced malleability: Some workpieces require some malleability, which is reduced after this case hardening process.
  • Volumetric changes: While less than the changes caused by other case hardening services, FNC still causes some growth to occur in your workpieces.
  • Tempering resistance: Workpieces that are exposed to extreme heat in the normal course of operations need tempering resistance. If you’re planning on tempering your pieces, then this resistance can be a limitation of FNC.

Whether a particular feature of ferritic nitrocarburizing/salt bath nitriding is an advantage or a limitation depends largely on your application. At Specialty Steel Treating, we offer this and other case hardening services that are designed to offer the critical features your workpieces need to compete in a competitive industry.

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