Nitriding

Nitriding

A computerised heat treatment furnace used in nitriding processes.

Nitriding is a heat treatment process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. This process is predominantly used for steel and other ferrous alloys. Nitriding is performed at relatively low temperatures compared to other heat treatment processes, typically between 500 and 550 °C (932 and 1022 °F).

Process

The nitriding process involves the introduction of nitrogen into the surface of a metal. This is achieved by exposing the metal to a nitrogen-rich environment, such as ammonia gas or plasma, at elevated temperatures. The nitrogen atoms diffuse into the metal surface, forming hard nitrides with the alloying elements present in the metal.

Types of Nitriding

There are several types of nitriding processes, including:

• Gas Nitriding: This involves the use of ammonia gas as the nitrogen source. The ammonia decomposes on the surface of the metal, releasing nitrogen atoms that diffuse into the metal.

• Plasma Nitriding: Also known as ion nitriding, this process uses a plasma discharge to introduce nitrogen ions into the metal surface. The plasma is generated by applying a high voltage to the gas, ionizing it.

• Salt Bath Nitriding: In this process, the metal is immersed in a molten salt bath containing nitrogen-bearing salts. The nitrogen diffuses into the metal from the salt.

Applications

Nitriding is used to improve the surface properties of metals, such as hardness, wear resistance, and fatigue strength. It is commonly applied to components such as gears, crankshafts, camshafts, and other parts that require high surface hardness and wear resistance.

Advantages

• Improved Surface Hardness: Nitriding significantly increases the surface hardness of metals, enhancing their wear resistance.

• Low Distortion: Since nitriding is performed at relatively low temperatures, it causes minimal distortion of the treated parts.

• Corrosion Resistance: The formation of nitrides on the surface can improve the corrosion resistance of the metal.

Disadvantages

• Limited Depth: The depth of the hardened layer is limited compared to other hardening processes.

• Long Processing Time: Nitriding can take several hours to achieve the desired surface properties.

Related pages

• Heat treatment
• Case hardening
• Surface engineering
• Plasma (physics)