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Measurement of Nitriding Layer for CNC Machined Parts

If you're interested in enhancing the wear resistance and fatigue strength of your CNC machined parts, nitriding may be a viable option. However, measuring the nitriding layer is critical to achieving the desired properties.

In this blog, we will discuss the different methods for measuring the nitriding layer on CNC machined parts, including microhardness testing, surface roughness testing, and metallographic examination. We will also explore the advantages and disadvantages of each method to help you choose the best approach for your specific application.

Additionally, we'll delve into the differences between nitriding and carburizing, as well as the advantages of testing the nitriding layer by metallographic examination. By the end of this blog, you'll better understand the importance of measuring the nitriding layer for CNC machined parts and how to select the most suitable method for your needs.

What is the Nitriding Process?

Nitriding is a surface hardening process often used on CNC machined parts to improve their wear, fatigue, and corrosion resistance. During the nitriding process, the part’s surface is exposed to a nitrogen-rich environment, typically through ammonia gas or other nitrogen-containing compounds.

nitriding process
nitriding process

The process is typically carried out in a furnace, and the temperature and duration of the process depend on the specific material and part geometry. The nitrogen atoms diffuse into the part’s surface, forming nitrides and increasing the surface hardness of the material.

One standard nitriding method for CNC machined parts is gas nitriding, which involves heating the part in a nitrogen-rich atmosphere. Another method is plasma nitriding, which involves using an electrically charged plasma to ionize nitrogen atoms and bombard the part’s surface.

When you nitride a steel part, it can become significantly harder, typically by 200-1000 HV (Vickers hardness), depending on the type of nitriding process used and the steel composition. The depth of the nitride layer also plays a role in the hardness, with deeper layers resulting in higher values. Plus, you can expect improvements in the tensile and fatigue strength of the part. With nitriding, the fatigue strength of steel parts can increase by up to 100% in general.

Nitriding is commonly used on steel and its alloys, including low alloy steels, tool steels, and stainless steels. Some specific steel grades that can be nitrided include 4130, 4140, 4340, 6150, and so on.

cnc machined parts before and after nitriding
cnc machined parts before and after nitriding

Nitriding has many benefits in the field of CNC machining:

  1. Increased surface hardness: Nitriding forms nitrides on the part’s surface, increasing its surface hardness and wear resistance. This can improve the part’s ability to withstand abrasion, erosion, and other types of surface wear.
  2. Improved fatigue resistance: Nitriding can increase the part’s resistance to fatigue failure by creating a compressive stress layer on the part’s surface. This can help to prevent crack initiation and propagation, leading to longer service life.
  3. Enhanced corrosion resistance: Nitriding can improve the part’s corrosion resistance by creating a nitride layer that is less susceptible to corrosion than the underlying material. This can be especially beneficial for pieces that are exposed to harsh environments, such as marine or industrial applications.
  4. Improved dimensional stability: Nitriding can reduce the risk of distortion and warping during heat treatment by minimizing the temperature gradient across the part. This helps maintain the part’s dimensional stability and reduces the need for post-nitriding machining or grinding.
  5. Cost-effectiveness: Nitriding is often a more cost-effective finishing option than other methods, such as plating or coating. It can also be performed on difficult or impossible parts to coat or plates, such as complex geometries or internal surfaces.

The Most Common Method of Measuring Nitride Layers on CNC Machined Parts

Our team provides comprehensive metallographic examination and Hardness method testing to guarantee the highest quality standards for your customers’ nitriding CNC parts. In this way, you can rest assured that all delivered components meet even the strictest customer requirements – with detailed test reports provided on request.

nitrided cnc part
nitrided cnc part

Metallographic Examination

metallographic examination
metallographic examination

The metallographic examination is a testing method used to analyze the microstructure and properties of metals and alloys. It involves preparing a small sample of the material by cutting, grinding, and polishing it to a mirror-like finish. The selection is then etched with a chemical solution to reveal the microstructure, which can be examined under a microscope to identify the various phases, grains, and other features of the material.

The metallographic examination can also often be used to evaluate the effectiveness of surface treatments, such as nitriding or carburizing, by examining the microstructure of the treated layer and the underlying metal. This can provide information about the thickness and uniformity of the treated layer, as well as any changes in the properties of the material.

The metallographic examination provides detailed information about the microstructure and properties of metals and alloys and is widely used in a variety of industries, including aerospace, automotive, and manufacturing.

Hardness Method

hardness method
hardness method

Various hardness testing techniques can be used to measure the nitride layer on CNC machined parts.

Microhardness testing involves using a microhardness tester to measure the hardness of the nitride layer by making a small indentation on the surface using a diamond indenter.

Surface roughness testing uses a profilometer to measure changes in surface roughness, which can help estimate the thickness of the nitride layer.

Eddy’s current testing measures changes in the electrical conductivity of the nitrided layer to provide rapid, non-destructive measurements of the nitride layer thickness.

The choice of hardness testing method will depend on the specific properties of the nitride layer and the intended application of the part. Microhardness testing is commonly used for measuring the hardness of nitride layers, while surface roughness testing and eddy current testing may be used to estimate the thickness of the layer.

Compare Metallographic Examination and Hardness Method for Measuring Nitride Layers on CNC Machined Parts

Metallographic examination and hardness testing are two powerful methods to provide insights into the nitride layers of CNC machined parts. Both approaches have their benefits, as a brief comparison reveals: one provides meaningful information on microstructure while the other allows for surface-level readings – both invaluable when it comes to gauging quality in this field.

Metallographic examination: This method involves preparing a thin section of the nitride layer and examining it under a microscope to evaluate the microstructure and composition of the layer. The metallographic examination can provide detailed information about the thickness, uniformity, and design of the nitride layer, as well as any defects or variations within the layer.

Hardness methods: These methods involve measuring the hardness of the nitride layer using specialized testing equipment, such as a microhardness tester or nanoindentation instrument. Hardness methods can provide information about the surface properties and wear resistance of the nitride layer, as well as its thickness and uniformity. However, they may give less detail about the internal structure or composition of the coating than metallographic examination.

AT-Machining’s Capability and service

At AT-Machining, we are experts in providing high-quality CNC machining services for a wide range of applications. Our state-of-the-art CNC machines are capable of producing complex and precision parts with tight tolerances, making them ideal for the demanding requirements of automotive, aerospace, and other industries.

Additionally, we offer a range of finishing services, including nitriding, to improve the hardness and durability of our machined parts. When it comes to measuring the nitriding layer of CNC machined parts, our team uses a variety of advanced methods, including metallographic examination and hardness testing, to ensure that every aspect meets our customers’ exact specifications.

metallographic examination report 1
metallographic examination report
metallographic examination report 3
metallographic examination report

We are committed to providing the highest quality products and services to our customers, and we are dedicated to helping you achieve success in your respective industries.


What Types of Parts Are Generally Suitable for Nitriding Processes?

  1. Gears: Nitriding can improve the wear resistance and fatigue strength of loads, making them more durable and longer-lasting.
  2. Shafts: Nitriding can improve the surface hardness and wear resistance of shafts, reducing the risk of surface damage or failure due to abrasion or erosion.
  3. Bearings: Nitriding can improve the fatigue resistance and corrosion resistance of bearings, helping to extend their service life.
  4. Dies: Nitriding can improve the wear resistance of dies used in forging, stamping, or other manufacturing processes, reducing the need for frequent replacement.

What is the Difference Between Nitriding and Carburizing?

Nitriding and carburizing are both surface-hardening processes used to enhance the wear resistance and fatigue strength of metals. Nitriding involves the diffusion of nitrogen into the surface of the part, which reacts with alloying elements in the metal to form a thin, hard, wear-resistant nitride layer. The nitride layer has a high surface hardness and improved wear resistance and enhances the part’s fatigue strength by introducing compressive stresses on the surface.

Carburizing involves the diffusion of carbon into the surface of the part, which reacts with alloying elements in the metal to form a thick, hard, wear-resistant case with increased toughness, impact resistance, and resistance to galling and fretting but lower surface hardness and wears resistance than nitriding.

Does Nitriding Have an Effect on the Accuracy of CNC Parts?

Yes. Nitriding affects the accuracy of CNC machined parts. This is because nitriding involves a high-temperature process that can distort the part if proper precautions are not taken. Additionally, the nitride layer can cause dimensional changes in the part due to its thickness and hardness. However, with careful process control and post-nitriding machining, these effects can be minimized, and the accuracy of the CNC parts can be maintained. It is essential to work with an experienced and skilled nitriding service provider who understands the potential effects of the process on the machined parts.

What Are the Disadvantages of Testing Nitriding by Metallographic Examination?

Time-consuming: The metallographic examination process can be time-consuming, requiring several steps such as sample preparation, grinding, polishing, and etching. This can result in longer lead times and increased testing costs.

Skilled personnel: Metallographic examination requires experienced personnel with the expertise and training to properly prepare and analyze the samples. This can add to the testing costs and limit the availability of testing facilities.

Sample size limitations: The size of the sample used for metallographic examination is limited by the size of the part being tested. This can be an issue for larger parts or parts with complex geometries.

Limited scope: Metallographic examination only provides a limited view of the nitrided layer and underlying metal. Other testing methods, such as hardness or corrosion resistance, may be needed to provide a more comprehensive analysis.

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Hey there, I’m Sam!

From AT-Machining, I’m a CNC Machining Expert in this field for more than 20 years.  We offer cost-effective machining services from China. Ask for a quote for your ongoing or upcoming projects now!

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