Do you feel lucky today, punk? The iconic Smith & Wesson 29 of Dirty Harry fame has a modern nitrocarburized cousin. And the infamous Glock 17 of Die Hard, 24 and many other movies and TV is also nitrocarburized.
Do you use cold, hard steel?
Tools, dies, and other metal components often require low-carbon, low-alloy steels. Or maybe you are creating something like cams, cutting blades, dies, or piston rods. Even medium and high-carbon steels sometimes need a final finish to improve resistance to metal fatigue.
Finished pieces are scuff and corrosion resistant. Are you familiar with nitriding and nitrocarburizing? These processes harden the surfaces of treated parts. But what is the difference?
Read on to learn more.
What Is Nitrocarburizing?
Nitrocarburization is a thermochemical diffusion process. Nitrogen, carbon, and a very small number of oxygen atoms diffuse onto the surface of steel or other ferrous alloys. This forms a surface compound layer and a diffusion layer.
There are two types of nitrocarburizing. Both types are low temperature, that is between 490°C and 580°C. This is below the tempering temperature of steel, which is over 600°C. The processes cause little or no distortion.
Nitrocarburizing is more commonly applied to low-alloy steels, mild steels and cast irons, but can equally be applied to any steel which is thermally stable at the treatment temperatures.
Austenitic and Ferritic Nitrocarburization
The first type is austenitic. Austenitic nitrocarburizing happens at the upper end of the temperature range. It has certain advantages:
- Enhances surface hardness
- High wear resistance
- Excellent fatigue strength
- Improved corrosion resistance
- Zero to minimal distortion
Ferritic nitrocarburizing is conducted at a lower temperature. It is often used instead of chrome plating. Its case depth is usually less than that of austenitic nitrocarburization.
Ferritic nitrocarburizing solves some of the problems of size change and distortion that are seen in higher temperature treatments.
Both types of nitrocarburization are used with steel and other iron alloy metals in a salt bath. Despite the name, the process is really a modified form of nitriding with carbon added.
Nitriding vs. Nitrocarburizing
Nitriding is another low-temperature process where nitrogen is transferred and taken up by the steel. It occurs around 510°C.
Most commonly, the term nitriding refers to steel heated in ammonia gas. The term nitrocarburization refers to steel treated in salt or exogas. The process is carried out in a sealed retort furnace at temperatures between 490°C and 530°C in a flowing ammonia atmosphere for up to 120 hours
Unlike nitrocarburization, in nitriding only nitrogen is transferred. The nitriding processes give the surface hardness and a distinct microstructure. However, the nitriding process takes tens to hundreds of times longer than nitrocarburization to achieve the same case depth.
Why Choose Nitrocarburization Over Other Processes?
More efficient process time is the primary reason to choose nitrocarburization over classic nitriding. Both processes offer case hardening, protection against abrasion and improvements in adhesive strength.
The compound layer of a nitrided or nitrocarburized steel is between 2 and 30 micrometers thick. Resistance to corrosion, friction, and wear properties are determined by this layer.
Under the compound layer is the diffusion zone, which goes deeper into the steel. The diffusion layer is around 0.1–0.5 mm. The hardness and depth of the diffusion layer determine static and fatigue strength as well as load-bearing capacity.
Depending on the alloy and process, virtually the same case depth and hardness can be achieved in 4 hours by nitrocarburizing that would take 24 hours with a classical nitriding process.
Applications
A hardness range of 300–1300 Vickers is obtained through this process. It depends on the steel alloy used. The hardness of the compound layer will determine how resistant the alloy is to wear.
Examples of applications are:
- Cylinders
- Pistons
- Gears
- Crankshafts
- Cams
- Barrels
Nitriding and nitrocarburizing can replace surface treatments like chromizing or black oxidizing. It also looks good.
Advantages to Nitrocarburizing for Certain Applications
For surfaces exposed to sand or other abrasives, nitrocarburizing provides abrasive wear resistance. After nitrocarburizing the surface hardness is higher than the hardness of the abrasive particles. However, this compound layer is quite thin, so this form of protection alone is only suitable in mild conditions.
On the other hand, nitrocarburizing improves the adhesive wear resistance of steel. The compound layer gives low friction. Opposing steel surfaces will have less tendency to stick together. Lubricant added to the porous outer layer tends to last longer.
Corrosion resistance is improved in comparison to other thermal and thermochemical treatments. Other surface hardening methods do not have the added benefit of an attractive deep black appearance.
As mentioned before the principal benefits of nitrocarburizing, are its low cost, shortened production cycle, and very small distortion of treated materials.
Choose Miheu Precision for Your Custom Nitrocarburizing Needs
Miheu is a family owned business with 40+ years of experience in heat treatments of steel. Facilities include steel heat treatment solutions such as traditional oil hardening and tempering in pit furnaces. In addition, Miheu has the most advanced systems for nitrocarburizing and all kinds of nitriding.
Let a Miheu expert help find the most appropriate solution for a specific steel requirement. Explore the annealing, quenching (oil or water) and normalization to start. Custom CNC machining, milling, and grinding are available. Additionally, sandblasting and bluing, dimensional control, and straightening are available to get the results wanted.
Reasons Miheu is superior to all other Slovenian steel processors:
- All in one place
- Our well-educated and dedicated team
- Strong, supportive culture
- Flexibility and short turnarounds
- High precision of our products and services
Let Miheu help you realize your complete product. High accuracy and high-efficiency Mazak CNC machining centers are waiting for your design. Custom component work is a specialty.
Contact us today to discuss how we can work together.