Normal force influence on smoothing and hardening of steel 03Cr16Ni15Mo3Ti1 surface layer during dry diamond burnishing with spherical indenter

Introduction. Sliding burnishing minimizes roughness and hardens of the steel surface. Quality of the formed surface and strength characteristics of the surface layer are determined by the burnishing speed, force and feed. Due to the danger of the surface micro-destruction during burnishing, the problem of selecting the favorable value of the normal force at a given feed arises. The current investigation aims to study the effect of normal force during dry diamond burnishing with a spherical indenter on smoothing the surface microprofile and strain hardening of the 03Cr16Ni15Mo3Ti1 austenitic steel surface layer. Research methods. Profilometry, scanning electron microscopy (SEM), microdurometry are used. Results and discussion. As the result of dry burnishing of deformation-stable austenitic steel 03Cr16Ni15Mo3Ti1 with a spherical indenter with a 2 mm radius made of natural diamond at a sliding speed of 10 m/min and feed rate of 0.025 mm/rev, it is found that in the investigated variation range of the burnishing normal force (100...200 N) the value of the smoothing coefficient of the initial steel surface microprofile after finish turning is 79...90 %, the greatest smoothing with a decrease in the average roughness parameter Ra from 1.0 to 0.1 µm is achieved at a force of 150 N; during diamond burnishing the initial (after finish turning) surface is hardened by 15...43 % (up to 382...444 HV), as the burnishing force raises from 100 to 175 N, a non-monotonic increase of the average microhardness from 409 to 444 HV 0.05 takes place; burnishing with a load of 175 N forms a gradient-hardened layer with a thickness of 300...350 μm with the appearance of individual microfractures in the form of beadings and micro-cracks on the surface, the maximum hardening is caused by the formation of a highly dispersed surface layer of 30...40 μm thick with a structure of highly dispersed austenite and the corresponding activation of grain-boundary and dislocation strengthening mechanisms. The results can be used when selecting the diamond burnishing parameters of parts made of corrosion-resistant austenitic steels according to the criteria for obtaining low surface roughness without significant microfractures and effective strain hardening of the surface layer.