Hardening of carbonaceous and alloyed steels by low energy nitrogen ions irradiation in arc discharge plasma

Abstract

Effect of low energy nitrogen ions irradiation in arc discharge plasma on structure and properties of a surface carbonaceous and alloyed steels (U8, St.30, PhVG, Ph12M, 5PhNV) was studied. The ion irradiation of steel specimens was performed vacuum facility with a triode gas plasma source based on thermionic cathode arc discharge ignited in atmosphere of pure nitrogen at low pressure. The nitrogen ions bombarded steel specimens surface carried out an energy 600 eV. The pressure of nitrogen at ion irradiation was 0,9...2 Pa. The temperature of irradiated specimens was not above 520°C. Studies were made into the structure, composition and microhardness of irradiated carbonaceous and alloyed steel specimens. Metallographic, X-ray diffraction and electron-microscope methods were used to investigate the surfaces of irradiated specimens. It is founded that microhardness of irradiated steel specimens surface increases by factors of 1.8 to 3. The thickness of strengthened layer reaches 80 ... 100 microns. Unstrengthening of bulk after nitrogen ions irradiation took place for carbonaceous steels with low heat resistance (U8, St.30). The bulk of material exhibits practically no unstrengthening after ion irradiation of alloyed steels with high heat resistance (PhVG, Ph12M, 5PhNV). The X-ray diffraction analysis performed for irradiated steels by nitrogen ions points presence of Fe 2-3/N (ϵ-phase), Fe4N (γ-phase) and carbide phase in most cases. Wear resistant and life-in-service of steel tools after nitrogen ions irradiation (U8, PhVG) were increased by factors of 2 or 3.