Alloy Effects on the Nitriding Process of H13 and AISI 4140 Steels: Preliminary Results

The state of the art for controlling the nitriding process is to measure and control the temperature and nitriding potential in the atmosphere to define the nitrogen concentration and phase stability at the steel surface. The experimental Lehrer diagram for pure iron is widely used in industry to specify the nitriding potential for the nitriding process of steels. However, applying the pure iron Lehrer diagram for the alloy steels can lead to erroneous results because of the different phase stabilities. To extend our previous work on the nitriding process simulation for steels, the systematic investigation on the role of alloy elements on the nitriding process has been conducted.

By using computational thermodynamics, alloy specific Lehrer diagrams, nitriding potential vs. nitrogen concentration diagrams, mole fraction of phases vs. nitrogen concentration diagrams, and mole fraction of phases vs. nitriding potential diagrams etc., are developed to systematically understand the effects of alloying elements on the phase evolution during nitriding. This analysis addresses the fundamental understanding on why certain steels are easier to be nitrided and how to control the nitriding process for specific steels. In the present work, H13 and AISI 4140 are selected for the nitriding experiments to verify the simulation results.