Nitro-carburizing of die steel 5XHM in the general-purpose highly active medium

Abstract

The purpose of the study. To develop a carburizer for nitrocementation based on amorphous carbon DG-100 and nitrogen-containing components urea (NH2)2CO, potassium iron-sulphide K4Fe(CN)6. Study the features of nitrocementation of X12MF steel in nitrogen-carbon medium at different temperatures.
Methods. Metallographic and X-ray diffraction analyses of nitrocemented samples were carried out using Quanta FEG650 electron scanning microscope and EMMA diffractometer. Wear tests of carbonitrided samples were carried out under conditions simulating the operation of die tools.
Results. Experiments have shown that modified layers on 5ХНМ steel begin to form already at 500°C. The depth of these layers depends on the processing temperature: at 550°C the depth is about 5 microns, and at 650°C 15... 20 microns. X-ray diffraction analysis revealed the presence of hexagonal carbonitride ε on the surface of steel treated at 550°C, and carbonitrides of two types (ε-phase and phase isomorphic to cementite) at 650°C. The microhardness of surface layers reaches 10 GPa at 550°C and 8...9 GPa at 650°C. The depth of diffusion layers depends on the urea content in the paste, while the influence of potassium iron-sulphide is evident only at temperatures above 600°C. Conclusion. Nitrocementation in a highly active nitrogen-carbon medium is an effective method of hardening of stamping tools made of 5ХНМ steel. At low temperatures (550°C), preferential saturation with nitrogen occurs, and at 650°C joint saturation with nitrogen and carbon. The resulting carbonitride layers have high hardness and wear resistance, which makes this method promising for hardening tools operating under increased loads.