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Frequently asked questions about the Nitriding process

Q: What materials are suitable for nitriding?
A: Certain types of alloy steel plus some tools steels

Q: Which materials are most commonly used for nitriding?
A: There are alloy steels specifically produced for nitride hardening, notably:
BS970: 722M24 (also known as EN40B)
BS970: 905M39 (also known as EN41)
BS970: 897M39 (also known as EN40C)
The following steels are also frequently used for nitriding:
BS 970: 708M40/709M40 (also known as EN19)
BS970: 817M40 (also known as EN24)
Tool steels suitable for nitriding include:
H13 tool steel
P20 tool steel
D2 tool steel
H10A tool steel
H21 tool steel

Many of the above steels may be marketed under trade names or as equivalent foreign specifications, please call if you need advice on the suitability of a steel for nitride hardening.
We also often treat “gauge plate” (01) steel, often referred to as ground flat stock, though not technically nitrideable it does produce a degree of nitride hardness, sufficient to provide abrasion resistance suitable for use in many applications. It is frequently nitrided to avoid the distortion resulting from normal “through” hardening.

Q: Will my components distort during nitriding?
A: The whole justification for nitride hardening is to produce high surface hardness with minimal, or zero, distortion. What can sometimes cause movement is the manufacturing process prior to treatment. Production induced stresses can relieve themselves during the process, leading to distortion. For this reason complex components are sometimes “stabilised” (i.e. stress relieved) part way through the machining process. This will not be necessary for most applications, but if unsure, please give us a call. All our furnaces are designed to process components in the vertical plane. You will see the effort we apply to jigging in photos elsewhere on this website.

Q: What hardness and case depth levels are achievable?
A: That depends principally on the chemical analysis of the material used and the core condition. Please look at our technical information section for advice, if your material is not listed, please call us.

Q: Can components be nitrided when their core is in the soft (annealed or as-rolled) condition?
A: To a degree – but it's not advisable. A pre-hardened part will exhibit notably superior surface hardness and greater durability.

Q: How do you test the result of the nitriding treatment?
A: We do not test customer's components unless specifically requested (and it's a very rare request). However we do place relevant test pieces in each furnace load. After the nitriding process is completed these test pieces are checked for surface hardness and case depth. The results are recorded and retained for every load treated.

Q: What exactly is meant by “case depth”?
A: Good question, most customers mean “total” case, some refer to “effective” case, but that needs to be specified. Some customers with very exacting requirements provide their own test piece made from the same material as their components. They usually specify a minimum hardness figure at a particular case depth. We grind down to that depth then test. This is the most accurate method of defining case depth – but it does cost extra, please contact us for more details.

Q: Can parts of a component be left soft, for further machining for example?
A: Yes – we use special paints to keep certain areas soft by insulating the component's surface from the nitriding atmosphere. This is an operation that we pride ourselves on, some parts require very intricate and extensive “masking”, for example racing car crankshafts. See photos elsewhere on our website, the green areas are where parts have been “masked”

Q: The process takes a long time compared to other hardening methods, why is this?
A: Nitriding is a diffusion process, which inevitably needs a lengthy treatment time. We offer cycles ranging from 12 to 90 hours duration. As nitriding specialists, we do run all cycles to a schedule, meaning you don't have to wait long until we assemble a load.

Q: Where can I get suitable nitriding steels?
A: If your normal supplier can't help, we have a database of specialist nitriding steel suppliers.

Q: Why should I consider nitriding over other processes that do not need specialised material?
A: That depends on your requirements – for some components, for example, racing car crankshafts or plastic mould tools, nitriding may be the only option. In other instances, you should consider the extensive remedial work that may be required following other processes. The nitride hardening process is worthy of close consideration for any wearing component of complex or lengthy configuration.

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