Nitriding of Internal Cylindrical Surfaces in Abnormal Glow Discharge

Abstract

The nitriding of cylindrical tubes with a length of 300 mm, an external diameter of 20 mm, and an internal diameter of 6 mm made of low-alloy structural steel 30CrN2MFA is investigated. The tubes are subjected to heat treatment (quenching at 860°C and aging at 600°C) before nitriding. Nitriding is performed at 500°C for 4 h in a N₂: H₂ = 1: 1 mixture at a total pressure of 5.3 mbar in abnormal glow discharge. The hardness after nitriding increases by 1.5‒2 times on both the external and internal surfaces of the tubes. The thickness of the hardened layer on the internal surface varies from 90 to 225 μm.