The Effect of Deformation on Structure and Properties of Surface Diffusion Layers Formed in Iron Alloys under Alloying by Nitrogen and Carbon

摘要

The influence of preliminary plastic deformation in the range of 5-70 % on the structure formation and mechanical properties of surface layers in iron-based alloys under diffusion alloying by nitrogen and carbon in ammonia and propane-butane gaseous environment at the temperature 853 K during 0.5-6 hours was studied. Surface diffusion layers were investigated by means of X-ray diffraction, microhardness and wear resistance tests. It was established that the surface layer of iron alloy after gas saturation by nitrogen and carbon consisted of ε -phase with the hexagonal closed packed crystal structure or θ - phase with the orthorhombic structure isostructural to cementite lattice and the solid solution of nitrogen and carbon in α -phase. The deformation within the range of 25-30 % substantially affects surface diffusion layer structure, phase and chemical composition and properties. The θ - phase was revealed in the layer after 25-30 % deformation and saturation in gas mixture of 90 % ammonia and 10 % propane-butane. Obtained in this way layers show maximum microhardness, wear resistance and thickness. The ε -phase was formed in the alloy after deformation out of the 25-30 % ranges. The lattice spacing of the α -phase containing nitrogen and carbon decreases non-linearly within the 25-40 % degree of plastic deformation. We assume that high strengthening of the surface layers results from interaction of disperse carbonitrides on such crystal lattice defects as dislocations.