Nitrate

Nitriding – Advanced Surface Hardening Process in CNC Machining

The nitriding process works by changing the chemical composition and microstructure of the material surface via controlled diffusion of nitrogen at high temperatures. Nitriding usually takes place between 500°C and 600°C, where nitrogen reacts with alloying elements such as chromium, aluminum and molybdenum in the steel, forming hard nitrides such as chromium nitride (CrN) or alumina nitride (AlN).

This change in surface composition creates a hard, wear-resistant layer, while the core of the metal remains soft and tough. The process primarily affects the top few millimeters of the material, resulting in a hard, thin layer known as the “nitrided layer.”

The rate at which nitrogen diffuses into the metal depends on the temperature and composition of the material. Cooling methods play a lesser role because no quenching is required. The use of controlled environments, such as ammonia or plasma, ensures that the nitrogen concentration remains consistent during treatment. The result is a uniformly hardened surface that improves the wear and fatigue resistance of the part.

Types & Variants of Nitriding Process

There are several variations of the nitriding process, each with specific advantages depending on the material and application:

• Gas nitriding: The most common method, in which parts are heated in a furnace in an ammonia-rich environment. The ammonia decomposes and nitrogen atoms diffuse into the metal surface.
• Plasmanitriding (Ion Nitriding): This advanced technique places parts in a vacuum chamber and bombards them with nitrogen ions through a plasma field. Plasmanitriding offers greater control over the depth and uniformity of the nitrided layer, making it ideal for precision components.
• Salt bath nitriding: A less common method in which parts are immersed in a molten salt bath with nitrogen-containing compounds. Salt bath nitriding creates a thinner nitrided layer than gas nitriding, but offers good process control.

Each method provides different hardness levels and layer thicknesses, with gas nitriding being the most versatile for large-scale applications and plasma nitriding providing the best control for finely tuned, precise treatments.

Material suitability & Preparation

Nitriding is especially effective on alloy steels containing elements such as aluminum, chromium and molybdenum, which form stable nitrides during the process. Common materials that are nitrided are:

• Nitration steel (e.g. 41xx, Nitralloy series)
• Tool steel (e.g., H11, H13)
• Stainless Steel
• Cast Iron
• Titanium alloys for highly specialized applications

Prior to nitriding, the parts must be thoroughly cleaned to remove any contaminants that may interfere with nitrogen uptake. Pretreatment processes such as degreasing, blasting or pickling may be necessary to free the surface of oxides, oil or scale. In addition, the parts must be machined to final dimensions, as post-processing after nitriding is difficult due to surface hardness.

Performance Enhancements & Benefits

The main benefits of nitriding are:

• Increased Surface Hardness: Nitriding can reach surface hardnesses between 800 and 1200 HV (Vickers hardness), providing excellent wear resistance.
• Improved Fatigue Strength: By hardening the surface, nitriding increases the fatigue life of parts, especially important for parts subjected to cyclic loads, such as crankshafts and gears.
• Increased Corrosion Resistance: The nitrided layer on the surface increases corrosion resistance, especially in nitrogen-rich environments.
• Reduced Friction: The hard surface reduces wear and friction between moving parts, increasing efficiency in applications such as engine parts.
• Minimal Distortion: Since nitriding occurs at relatively low temperatures and requires no quenching, the risk of distortion or cracking is minimized, making it ideal for precision components.

Applications & Relevance in Industry

Nitriding is crucial in industries that require high wear, fatigue and corrosion resistance. Key sectors include:

• Aerospace: Applied to turbine blades, landing gears and actuator components to withstand extreme stresses and high cyclic fatigue.
• Automotive: Crankshafts, camshafts, gears and valves benefit from nitriding due to increased fatigue strength and wear resistance.
• Tool and die construction: precision tools and dies require extreme surface hardness to withstand wear and maintain accuracy in long-term use.
• Medical devices: Nitrided surfaces are used in surgical instruments and implants to improve biocompatibility and longevity.

Nitriding meets stringent industry standards such as AMS 2759 for aerospace and automotive heat treatments, ensuring that parts meet critical performance and durability requirements.

Customization & Process Optimization

With us, you can count on fully customized nitriding processes tailored to each customer’s specific needs. By adjusting temperature profiles, gas mixtures and treatment times, we optimize the depth and properties of the nitrided layer based on the intended application. This allows us to refine the nitrogen concentration to balance surface hardness and toughness, ensuring optimal performance in high-load environments.

Our plasma nitriding capabilities offer exceptional precision in surface treatment, allowing us to treat parts with complex geometries and tight tolerances with minimal distortion.