Modification of Nanostructured Maraging Steels Surface with Atmospheric Nitrogen at Steel Hardening in Confined Space

摘要

The specific features of atmospheric nitrogen surface nitriding of cold-rolled foils (the value of the coherent-scattering region is 10 nm) from stainless maraging steels after hardening in a confined space containing air are considered. Thermodynamic evaluation of the probability of influence caused by the confined space air on the phase transformations and solubility of the atmospheric nitrogen shows that the surface modification takes place in two stages: at the first stage, oxidation dominates; and at the second stage, predominantly the nitrogen absorption by the surface takes place. While changing, the nitrogen solubility reaches the maximum in the range of 10 - 22 % of Cr and has the largest values at the air pressure in the range of 0.001 - 0.04 MPa. Based on the nitrogen solubility diagrams, optimal conditions for the nitrogen austenite formation without the formation of nitrides are established. The developed method for nitriding allows the formation of nitrogen austenite layer of about 20 μm in thickness in the surface of nanostructured maraging steels without deteriorating the surface electrochemical properties.