Liquid Nitriding / Salt Bath Nitriding (SBN) / Ferritic Nitro-Carburizing (FNC)

Overview

Liquid nitriding is a subcritical surface enhancement process with one of the longest track records of success of any case hardening technology. It is widely used to enhance the wear and corrosion resistance of plain carbon steels; low alloy steels; and stainless steels.

In a liquid nitriding bath which is maintained between 500 - 630°C (930 - 1165°F), nitrogen-bearing salts produce a controlled and highly uniform release of nitrogen at the surface of the workpiece. Nitrogen diffuses into, and chemically combines with, nitride-forming elements in the metal, producing, through a catalytic reaction, a tough, ductile compound layer with exceptional mechanical properties. This hard compound layer has wear properties that are 200% to 1000% greater than the original material, and greatly enhanced resistance to corrosion, galling and scuffing. Below the compound zone is another distinctive region, the diffusion zone. This zone results from the progressive diffusion of nitrogen and the formation of a solid solution of nitrogen in the base material. The diffusion zone contributes a critical fourth benefit of salt bath nitriding: substantial enhancement of fatigue strength, typically 20% to 100%.

Nitrogen Diffusion
Nitrogen Diffusion
After Nitriding, the surface can be oxidized to create a 1-3 μm corrosion resistant, black iron-oxide layer

After Nitriding, the surface can be oxidized to create a 1-3 μm corrosion resistant, black iron-oxide layer

Oxidized Sub-Micron Porosity

Oxidized Sub-Micron Porosity

Sub-micron size surface porosity:

  • Can be tailored for specific applications
  • Very useful for impregnating with especially formulated oils & polymers significant improvement in corrosion protection & run-in characteristics
  • Porosity needs to be controlled – excessive amounts can make compound layer friable

Liquid Nitriding modifies the surface metallurgy and properties of ferrous materials

Liquid Nitriding modifies the surface metallurgy and properties of ferrous materials