Nitride components and nitro carburizing material phase

What is a nitride?

Nitride is a kind of thermal chemical processes, including the surface of the iron metal (such as steel) added the nitrogen.This makes the nitride layer is very hard and wear-resistant, and significantly improve the fatigue strength and corrosion resistance.

There are two commonly used nitride options:

• Metal nitride: only use nitrogen to enrichment.This is typically used for low carbon and low alloy steel and iron molybdenum, titanium, aluminum and alloy.
• Nitro carburizing: in addition to nitrogen and enrichment of metal by using a small amount of carbon.The most commonly used for iron base alloy.

Preparation of nitride and nitro carburizing component challenge

On nitriding and nitro carburizing components, most often the need for metallographic analysis, to control the manufacturing process of thermochemical nitriding process, and failure analysis.In the two applications, metallographic analysis method remains the same.

Metallographic scientist in the preparation of nitride and two major challenges facing the nitro carburizing components.


Figure 1: sample and Mosaic resin shrinkage clearance between capture abrasive and may cause nitride layer peeling off.


Figure 2: round edge: edge protection layer may lead to poor not focus under magnification.

For a complete description about how to deal with these challenges,Please download the complete application instructions.

The composition of the nitride layer

The nitride layer consists of two parts, namely the compound layer and diffusion zone.The thickness of two layer depends on various parameters, including the substrate metal components, the length of the thermochemical nitriding process and the use of temperature.

The composition of compound layer
Compound layer formed by two iron nitride phase: epsilon (Fe₃N) and gamma '(Fe₄N).Because it keep white after etching with nitric acid ethanol, which is called "white layer", the compound layer does not contain any metal.On the contrary, it is made of iron and nitrogen phase composition, not of metal.This layer is relatively hard, and the hardness increased with the decrease of the hardening layer depth.Porous area seen in compound layer in the outer region.

The diffusion area of
Diffusion zone is located in the compound layer directly.It contains nitrogen in solid solution, as well as alloy elements, such as tungsten, molybdenum, chromium, and aluminum) formation of acicular stable metal nitrides.These nitride etching needle can be visible so that the diffusion zone and its thickness can be measured.

If you want to learn more about the composition of the nitride layer, thickness and hardness of information, pleaseDownload the complete application instructions.


Figure 3: the composition of the nitride layer.

Thermochemical nitriding process

There are three commonly used nitriding process.Choice of method depends on the specific application finally nitride components.

The following brief introduction of the nitriding process.If you need to know the process in detail, and how each process affects the characteristics of the nitride components or parts, pleaseDownload the complete application instructions.


Salt bath nitro carburizing
After preheating, dip components composed of alkaline cyanic acid salt and alkali carbonate salt bath.Alkaline cyanate by oxidation and thermal release spread to nitrogen and carbon on the surface of the metal.

After salt bath nitro carburizing, quenching of components in the oxidizing salt bath.This produces a black iron oxide (Fe₃O₄), which is used to fill the porosity of the compound layer, and provide additional corrosion protection.

• Typical application: used in auto parts, such as the piston rod, CAM shaft and gear, as well as for aircraft parts, offshore and mechanical engineering industries.

Nitro gas nitriding and gas carburizing
A sealed in gas nitriding, the component of bell-shaped nitriding furnace.When reach the nitriding temperature, ammonia into the melting pot.When ammonia react with metal, it will break down and release the spread to new nitrogen on the surface of the metal.In the process of gas nitro carburizing, carbon is added to the gas.

• Typical application: the machine tool spindle, nodular cast iron pump shell, door lock device, and used for gas compressor piston pump components.

Plasma nitriding and plasma nitro carburizing
Plasma nitriding is carried out in a nitrogen/hydrogen atmosphere.The plasma is produced in the high voltage vacuum chamber.In this environment, ACTS as the cathode metal components, vacuum container ACTS as an anode.Plasma carburizing process are the same, but will add carbon gases.

• Typical application: as the plasma nitriding allows the use of a variety of nitriding layer, so these components can be used for many different applications.The camshaft and crankshaft, including high performance motor machine spindle, automotive die, corrosion resistant engine valve and high speed steel cutting tools.

Figure 4: use 1% ethanol nitrate etching salt bath nitro carburizing steel alloy (16 mncr5).Diffusion zone is etched into dark, with the compound layer of porous area display is white.


Figure 5: nitro gas carburizing carbon steel (580 ° C, 1.5 hours).


Figure 6: plasma nitro carburizing carbon steel (570 ° C, 6 hours).Two nitride layer porous area, and a very high surface finish.

Nitride components and nitro carburizing metallographic preparation

Nitride and nitro carburizing components during the preparation of the major challenges is () of porous zone break and compounds (area) in the first element of the grinding crack.In addition, the incorrect sample set and excessive polishing with a soft cloth can lead to edge roundingoff, this makes under high magnification thickness measurement and evaluation is very challenging.


Figure 7: cracks occurring in the process of preparation of coating.

Below, we can overcome these challenges concise advice is given.In order to more fully understand how to prepare nitride accurately and rapidly and nitro carburizing components for metallographic analysis, pleaseDownload the complete application instructions.

Cutting: how to avoid damage the nitride layer

• Water cutting machine on the cross section of nitride and nitro carburizing components.
• Using alumina cutting wheel.Choosing cutting wheel, please choose according to the hardness of the component.

Set: how to avoid the nitride and nitro carburizing shrinkage clearance in a sample

• Recommend the use of fiber reinforced resin (such as DuroFast)Thermal compression set.
• In order to improve the edge protection, please set sample before cutting sample with a thin layer of pure copper foil.

In addition, still can increase copper inlaid resin and coating contrast effect, the timeshare is especially useful in group processing oxidation.


Figure 8: high alloy steel (X45CrSi9V), nitro carburizing salt bath, using 1% ethanol nitrate oxide etching.Diffusion zone is etched into dark.The compound layer can't apart from the sample with resin.


Figure 9: same as the figure 8, the use of copper foil Mosaic.Can clearly see that the compound layer on copper foil, and can be measured.


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Grinding and polishing: how do you ensure that nitriding and nitro carburizing sample good edge protection

• Shall be carried out using silicon carbide foil/sand paper plane grinding.
• In order to ensure good edge protection:
  - in the rigid fine grinding disc (MD - LargoUse for fine grinding of diamond suspension).
  - then in satin woven fabric with diamond polishing cloth acetate fiber cloth (MD - DacPolishing).
  - use 1 mu m diamond or silica gel on short final polishing.

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Tips nitride coating grinding and polishing


Etching, etching and nitro carbide nitride sample

• In order to evaluate porous area, please first check the nitride coating, then etching metal nitride sample.
• With nitric acid of 1-3% ethanoletchingShow white compound layer.In the nitride alloy diffusion zone will darken.
• In order to identify the nitride diffusion zone of low carbon steel, please send sample when heated to 300 ° C for 45 minutes, then using 1% ethanol nitrate for etching.

Figure 10: alloy steel (42 crmo4), gas nitriding (36 hours under 510 ° C) and etched with the 1% ethanol nitrate.Dark diffusion area, white compound layer and porous area visible.

Download the complete application instructions, nitride and nitro carburizing component preparation methods of mature step by step.

Components and nitro carbide nitride material phase components

Thermal chemical adding nitrogen nitriding process for surface, and in some cases, add a small amount of carbon, so as to improve the wear resistance and corrosion resistance of metal components.There are three kinds of nitriding process, and will ultimately achieve very hard nitrides surface, the surface includes a compound layer and a diffusion zone.

Nitride components and nitro carburizing components of metallographic analysis is mainly used to control the quality of the nitriding process and analysis of fault component.

In dealing with nitride and nitro carburizing component, metallographic, faces two main challenges: in the process of cutting and grinding, nitride layer may be broken or crack;Incorrect set sample and polishing can lead to edge preparation the effect not beautiful.In order to overcome these challenges, metallographic scientists should follow designed for nitride and nitro carburizing component design specific methods, such as mentioned in this application notes.

Click here to downloadComplete application instructions.


Figure 11: ferritic nodular cast iron, gas nitriding, etched with 3% nitric acid alcohol (500 x).

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All images by the Chinese application experts Charily Zeng

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