Ferritic Ion/Plasma Nitrocarburising - Explained

The title of this heat treatment might be a bit of a mouthful — Ferritic Ion/Plasma Nitrocarburising — but it describes the process accurately.

So let’s break it down and understand what this heat treatment is all about.

Ferritic Region & Crystal Structure

First, let’s start with the term ferritic.

Let us take a basic steel grade from the iron-carbon phase diagram - AISI 1045. To keep things simple, we'll ignore other alloying elements for now. This type of steel is primarily ferritic — meaning its crystal structure is body-centered cubic, or BCC. A Ferritic steel is relatively soft and ductile. Now, if we want to change those properties — for instance, to increase hardness — we need to alter the steel’s structure.

One way to do this is through heat treatment. If we heat the steel above the eutectoid temperature, which is around 727 degrees Celsius, it transforms from ferrite (BCC) into austenite (which has a face-centered cubic, or FCC, structure).
Then, by rapidly cooling — or quenching — we can form martensite, a hard and brittle phase with a body-centered tetragonal (BCT) structure.

Phase changes of the steel above 727 C	Ferritic Ion/Plasma Nitrocarburising temperature

But in ferritic nitrocarburising, we stay below that eutectoid temperature. That means the steel retains its ferritic structure throughout the process — hence the name.

Nitrocarburising Basics

Now let’s look at the "Ion/Plasma Nitrocarburising" part.

In our explanation on plasma nitriding, we discussed how alloying elements [like chromium, molybdenum, vanadium, aluminum, or titanium] affect the surface hardness and case depth. These elements form hard nitrides during the process.

But what happens when your steel doesn’t contain many strong nitride formers? Steel grade AISI 1045 does not contain any of the alloy elements that are strong nitride formers.

Nitrogen diffuses into the crystal structure, and distorts it, which increases the hardness, but not as much as when it forms nitrides.

Nitrocarburising offers a way to significantly boost surface hardness and wear resistance — by promoting a thicker white layer compared to standard nitriding.

Comparison in surface hardness after nitriding between AISI 1045 and AISI 4142	The formed white layer on top increases the surface hardness greatly.

Key Differences from Standard Plasma Nitriding

There are three main differences between ion/plasma nitriding and nitrocarburising:

1. Carbon Addition:
   A small amount of carbon-bearing gas — [like CO or hydrocarbons] — is added to the plasma atmosphere. This helps form a thicker white compound layer.
2. Temperature:
   The process runs at a slightly higher temperature than standard nitriding, though still below 727°C to maintain ferritic structure.
3. Time:
   The treatment time is usually shorter, but still long enough to form an effective white layer.

Applications:

Ferritic ion/plasma nitrocarburising is widely used across industries — from automotive components like gears and shafts, to tools and welding tables — wherever enhanced surface wear resistance is required without altering the core toughness.

Be sure to check our video for a visual explanation: