Expected Changes Out of the Standard Nitriding Process
26 February 2021Standard nitriding process is a type of heat treating process that is being utilised by many manufacturers. This process is done through the introduction of nitrogen into the surface of a metal, allowing it to obtain a case-hardened surface. The case-hardened surface of a metal part becomes possible as it is being held at a temperature below on which its crystal structure transforms into austenite on heating. The transfer of nitrogen into the metal surface is initiated by subjecting the material to ammonia.
What is great about nitriding is that it maximises lower temperature and less part distortion compared to other case-hardening processes and techniques. It is also easier to control, especially when it comes to process parameters. One limitation of this process, however, is that it tends to create a more brittle surface for a high surface-hardness case compared to one that has undergone the carburising process.
Once the standard nitriding process is carried out, the following properties of a metal part or components are expected to be changed and altered.
Surface Appearance
Metal parts and components that are subjected to the standard nitriding process are typically known to have a dull, matte-grey colour. However, there are instances where additional steps are made, which then convert the parts’ surfaces into darker colours.
Case Structure
Metal parts that are processed through standard nitriding are expected to be diffused with nitrogen, but there are limitations on how far it can reach from a part’s surface, especially during the nitriding period. As more alloy elements are eliminated from the solid solution, the nitrogen will then diffuse farther into the metal part and subsequently increase deep case. The case depth, after all, will depend on the amounts of alloy elements that the nitrogen must reach with and interact with before the diffusion takes place.
Dimensional Changes
The standard nitriding process enables the parts to slightly increase in size due to the occurrence of an increasing volume in the case. The increasing volume enables the part to stretch its core, resulting in tensile stresses in the core that are compensated equally by compressive stresses in the case. All these changes materialise once the parts have already cooled to room temperature. Factors that can affect dimensional changes include the overall composition of a part, tempering temperatures, time and temperature of nitriding, the relative thickness of the case or core, part shape, and areas marked off.
Amount of Growth
The amount of growth during the standard nitriding process is normally constant for parts that are processed in varying batches under fixed processing cycle. Allowance can only be made once the amount of growth for a part has been identified. Though, sharp corners or edges must be avoided on parts that have been subjected to the standard nitriding process since they are vulnerable to chipping.
Some of the most common metals that can undergo the standard nitriding process include high-carbon, low-alloy steels that include alloy elements of titanium, aluminium, and/or molybdenum. As for applications, the same process can be used for gears, crankshafts, camshafts, valve parts, extruder screws, die-casting tools, forging dies, extrusion dies, injectors, plastic-mould tools, and many more. For more information about the standard nitriding process, feel free to contact us at Alpha Detroit Heat Treatment.
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