{"id":21635,"date":"2023-06-12T14:54:20","date_gmt":"2023-06-12T11:54:20","guid":{"rendered":"https:\/\/fractory.com\/?p=21635"},"modified":"2024-04-10T12:22:25","modified_gmt":"2024-04-10T09:22:25","slug":"nitriding-explained","status":"publish","type":"post","link":"https:\/\/fractory.com\/nitriding-explained\/","title":{"rendered":"Nitriding Explained – How It Works, Benefits & Types"},"content":{"rendered":"

Many types of heat treatment methods<\/a> are used across the industry to make metals more suitable for different applications.<\/p>\n

In this article, we explore a thermochemical surface treatment<\/a> process that hardens a metal’s outer surface by increasing its nitrogen concentration.<\/p>\n

What Is Nitriding?<\/strong><\/h2>\n

Nitriding is a type of case-hardening<\/a> process that hardens the outer layer of a part by adding nitrogen to its surface.<\/strong> The added nitrogen combines with iron and other alloying elements in the metal’s composition to form hard metallic nitrides.<\/p>\n

As the nitrogen reaches only a certain depth, the interior of the part retains its original properties and, therefore, is relatively softer. We can achieve a final surface hardness<\/a> of up to 76 HRC (90 HRA) through the nitriding process.<\/p>\n

The hardness layer (case depth) generally has a thickness of 200\u2013300 \ud835\udf07m (0.0002m) but can be up to 2 mm in some applications. We can control it by changing factors such as the duration of exposure, nitriding temperature, gas flow, etc.<\/p>\n

The nitriding process creates a compound layer – a white layer as the outer layer with a diffusion zone underneath. The diffusion zone consists of the absorbed nitrogen as well as the hard nitride precipitates.<\/p>\n

Nitriding is carried out at temperatures below the austenitisation temperature of steel. The austenite formation begins at 727 \u00b0C<\/a> (1340 \u00b0F) for plain carbon steel but varies for alloy steels based on composition.<\/p>\n

Thus, nitriding is typically carried out at a process temperature between 500 and 550 \u00b0C (930 – 1022 \u00b0F) and up to maximum temperatures of 620 \u00b0C (1150 \u00b0F).<\/p>\n

The nitriding process can take anywhere from 4 to 100 hours. Beyond 100 hours, the layer thickness increases at a very slow rate, making the process unfeasible.<\/p>\n

When Is Nitriding Used?<\/strong><\/h3>\n

Nitriding is not used on all types of steel. It can be used for plain carbon steel, but it is generally preferred for low-carbon alloy steels that have nitride-forming elements such as aluminium, molybdenum and chromium. These elements facilitate precipitation hardening<\/a>.<\/p>\n

Apart from steels, nitriding also provides good results with titanium, molybdenum and aluminium alloys<\/a>.<\/p>\n

Nitriding Benefits<\/strong><\/h3>\n

Nitriding provides many advantages over popular case hardening procedures such as carburising. Some of the benefits of using nitriding are as follows.<\/p>\n

Lower temperature<\/h4>\n

The nitriding process works at temperatures of about 550 \u00b0C (1022 \u00b0F), which is well below the temperatures of other processes such as carburising<\/a>. Nitrided parts, therefore, undergo reduced distortion and deformation and offer very good dimensional control.<\/p>\n

High surface hardness with a ductile core<\/h4>\n

Nitrided parts have high surface hardness coupled with a ductile core. The combination of these properties provides a wear-resistant surface with a flexible core that can handle impact loads much better than a hard material.\u00a0<\/p>\n

Thus, we can use nitrided components in applications where impact loads are present along with exposure to abrasives or friction<\/a> without worrying about sudden failure under high loads.<\/p>\n

Increased corrosion resistance<\/h4>\n

The nitriding process improves the corrosion resistance of some steels. The deposited hard nitride layer prevents the formation of pits that would eventually corrode through pitting corrosion<\/a> in an untreated part. To obtain maximum corrosion resistance, the white layer formed after the nitriding process must be maintained intact.<\/p>\n

Plasma nitriding, for instance, improves the corrosion resistance of 410 stainless steel<\/a> as the iron nitride layer on the surface protects the metal underneath from a corrosion attack.<\/p>\n

But there are cases where nitriding increases the corrosion rate. For instance, when plasma nitriding was performed on martensitic X17CrNi16-2 stainless steel, its corrosion resistance actually decreased. This is mainly because of the formation of chromium nitride which reduces the initial corrosion protection offered by chromium in the solid solution.<\/p>\n

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