Effect of ultrasonic surface treatment of steel 40Kh13 on the microstructure of nitrided layer formed by high-intensity low-energy implantation with nitrogen ions

Abstract

X-ray diffraction and transmission electron microscopy were used to study the microstructure and phase composition of surface layers of steel 40Kh13 subjected to irradiation with high-intensity low-energy ion beams, ultrasonic surface modification, and combined treatment including ultrasonic surface modification and ion implantation. It was found that the ultrasonic modification of steel surface leads to changes in the structure of tempered martensite and the formation of grain structure with a grain size of 0.3 μm and nanosized special carbides Cr23C6 in the martensite lamellae. The ion implantation into this steel results in the formation of a nitrided layer consisting of a nitride region, which represents a mixture of several phases (α-, γ′-, ɛ, and ultrafine chromium nitrides), and a zone of internal nitriding (α″ and nitrogen-containing martensite αN). The preliminary ultrasonic modification causes an increase in the nanohardness and in the thickness of the nitrided layer, which is due to the more intense penetration of nitrogen atoms into the surface layer and an increase in the volume fraction of iron nitrides and density of ultrafine chromium nitrides in this layer.