For customers who need steel parts with improved toughness, higher hardness and retained ductility with less risk for distortion, nitriding is a good candidate. But finding the right heat treater to perform the work can be difficult if you’re unfamiliar with the nitriding process, and it’s even harder given the sea of trade names that permeate the industry.
Nitriding is an umbrella term covering case hardening processes that achieve the above-mentioned characteristics via the introduction and interaction of nitrogen and carbon at a part’s surface. Nitrogen is soluble in iron at elevated temperatures and diffuses into the surface of steel parts, forming both a compound layer and a diffusion zone that increase surface hardness.
At Paulo, we believe in clarity. That means untangling trade names to reveal the truth behind variants in the nitriding process: There are many ways to reach the same metallurgical results.
The truth about trademarks
Trademarked heat treatments give customers the impression that nitriding processes differ wildly from one another. The opposite is true: The ways nitrogen and carbon are supplied to part surfaces can be subtly tweaked —and therefore patented— but they all achieve similar part characteristics.
Because different trade names often only indicate different means to reach an identical end, it’s important to understand the end first and then work backwards into finding the appropriate heat treatment.
Use this rundown of nitriding variants to learn more about trade names, processes and the parts commonly treated via each method:
Ferritic nitrocarburizing (FNC) – Ferritic nitrocarburizing is a form of nitriding that achieves desired part characteristics while maintaining ferritic temperatures (between 975 and 1,125 degrees Fahrenheit). These temperatures are comparatively low; the process significantly reduces the risk that parts will crack or distort. For this reason, FNC is a popular treatment for machined parts like automotive powertrain components, cams, transmissions and brake rotors as well as firearm components like slides and barrels.
Compared to other nitriding variants, FNC delivers a shallower hardness depth and its treatment cycles are comparatively short. It is executed via the following media:
- Liquid salt bath – Parts are submerged in molten salt baths. Specified case depth and porosity dictate the blend of salt used. Patented blends to deliver the nitrogen and carbon resulted in trade names like Melonite, Tufftride, Tenifer, Arcor and Nu-Tride.
- Fluid bed FNC – Parts are placed in pots of heated sand that’s agitated by gaseous compounds that contain the nitrogen and carbon needed to achieve the desired finished qualities. Trade names include Nitro Wear, Oxy-Blue, Tectyl Nitro Black and Dyna Blue.
- Gas nitrocarburizing – This FNC method is carried out in a furnace; the nitrogen and carbon are injected into the furnace as gaseous compounds. Again, the compounds and their concentrations can vary depending on what the specifications call for, which has resulted in a host of trade names including Ni Temper, TriNiding, Trinide, Nitroflex, Lindure, Nitro Tec, Epsolite, MicroWear, MicroTect, MicroCoat, Oxy Nitrocarburizing, Vario Nitrocarburizing, QNN Nitriding, QNF (ferritic), QNA (austenitic), QNO (oxidize), Rapid Black, Controlled, Nitroc and Dyna Brite.
FNC has become increasingly popular because it works across a broad range of parts and industries. Because the delivery of nitrogen and carbon via FNC is more controllable compared to other heat treatments, desired hardness can be achieved without the need for tempering following treatment. That keeps treatment costs comparatively low.
Gas nitriding – In gas nitriding, parts are heated in sealed furnaces. Nitrogen is injected in the form of ammonia gas. Heat causes the ammonia molecules to break apart, freeing the nitrogen atoms to diffuse into parts.
While FNC methods target compound layer characteristics at a part’s immediate surface, gas nitriding focuses on the diffusion zone beneath the compound layer. Hardness depths achieved via gas nitriding are comparatively deeper than those achieved by FNC; gas nitriding treatments take significantly longer (from several hours to a couple days) and are therefore more costly.
Gas nitriding is often used on gears and both hydraulic and fuel pump components.
How can we help
Manufacturers can make better heat treatment decisions when they’re armed with clear, usable information that allows them to separate heat treatment from patents and trade names. If you have any questions or need some advice, contact us to reach metallurgists who are ready to assist. You can also learn more about why outsourcing heat treatments like nitriding is the right move for your business by downloading the guide below.
Trademarks cited in this article are the property of their respective owners.