Three Nitriding Processes in Heat Treatment: Overview and Translation

1. Ion Nitriding 

Principle:

• Utilizes glow discharge in a vacuum chamber where the workpiece acts as the cathode.
• Nitrogen/hydrogen gas is ionized, forming a plasma zone. Positive ions (N⁺, H⁺) bombard the workpiece surface, converting kinetic energy into heat to reach the desired temperature.
• Surface purification occurs via atomic sputtering, while nitrogen diffuses into the surface via adsorption and diffusion.

Key Features:

• Controlled Parameters: Atmosphere composition, pressure, electrical parameters, and temperature regulate the surface compound layer (“white layer”) and diffusion layer structure.
• Advantages: Faster processing, minimal distortion, and precise control over microstructure.

2. Gas Nitriding 

Objectives:

• Primarily enhances surface hardness and wear resistance.

Methods:

• Isothermal Nitriding:
  • Constant temperature (480–520°C) and ammonia decomposition rate (15–30%).
  • Long duration (~80 hours), suitable for shallow layers and strict distortion requirements.
• Multi-Stage Nitriding:
  • Segmented temperature, decomposition rate, and time (e.g., 50 hours total).
  • Deeper layers but higher distortion risk due to elevated temperatures.
• Corrosion-Resistant Nitriding:
  • Higher temperatures (550–700°C) and shorter durations (0.5–3 hours).
  • Forms chemically stable compound layers for resistance to wet air, steam, and combustion gases.

3. Nitrocarburizing 

Mechanism:

• Conducted below the Fe-N eutectoid temperature.
• Simultaneous nitrogen and carbon diffusion:
  • Carbon accelerates nitrogen diffusion and high-nitrogen compound formation.
  • Nitrogen increases carbon solubility, reducing compound layer brittleness.

Applications:

• Enhances fatigue strength, corrosion resistance, and lubricity.
• Commonly used for low-alloy steels (e.g., automotive gears, dies).

Summary of Key Differences