Effect Of Cold Deformation On The Friction Wear Property Of High-nitrogen Nickel-free Stainless Steel

The high-nitrogen nickel-free stainless steel (HNNFSS) used in this paper was melt by nitrogen-pressurized induction melting method and cold rolled to get different deformation which were 20%,40% and 60%; the effect of cold deformation on the microstructure, tensile property, corrosion resistance and friction wear property of HNNFSS were mainly studied. The microstructure and phase were analyzed using optical microscope (OP), transmission electron microscope (TEM) and X-ray diffraction (XRD). The mechanical properties were measured via tensile tests, its corrosion behavior was studied by means of electrochemical tests, and the friction wear experiments were carried out on the Tribometer, after which worn surfaces were analyzed using scanning electron microscope (SEM), microhardness tester and X-ray photoelectron spectroscopy (XPS). The main results were summarized as follows:HNNFSS possessed stable austenite structure. The deformation mechanism transformed from dislocation planar slip to twinning gradually as the strain increased. Due to cold deformation, both strength and hardness of HNNFSS increased rapidly, while its plasticity and toughness were decreased. The fracture morphology of HNNFSS was mainly characterized by dimples, together with some tear ridges.In dry friction wear tests, both cold deformation and load had significant effect on the friction coefficient-time curves. Under same load condition, as cold deformation increased, the wear rate of HNNFSS decreased first and then increased, however, its friction coefficients were mostly same. Because of increasing load, the wear rate of HNNFSS increased a lot and its friction coefficients decreased gradually. The main wear mechanism was abrasive wear together with brittle flaking, and the latter became important with increasing cold deformation and load. Moreover, when the friction pair was GCr15 or 304 steel ball, cold deformation had different influences on the friction wear property of HNNFSS and the wear mechanism changed correspondingly.The electrochemical tests showed little effect of cold deformation on the corrosion resistance of HNNFSS in the same solution. In the corrosion-wear tests, the friction coefficient kept relative stable with time; the friction coefficients of HNNFSS were nearly equal in the same solution in spite of increasing cold deformation and friction coefficients obtained in the phosphorus-containing solutions were smaller than those obtained in the phosphorus-free solutions. When the distilled water,0.9%NaCl and 3.5% NaCl solutions were choosed as the corrosive media, HNNFSS exhibited improved wear resistance as cold deformation increased; however, the wear resistance of HNNFSS decreased gradually with the increase of Cl" concentration. In PBS solution, there was no obvious difference in the wear resistance of HNNFSS with different cold deformation; nevertheless, as cold deformation increased, HNNFSS’s wear resistance in Hank’s solution was improved monotonously and that in the pH6.0Hank’s solution increased first but then deceased. In the corrosive media, the main wear mechanism was abrasive wear companied with some pitting corrosion. In Hank’s solution, HNNFSS was more wear-resistant than 317L stainless steel, but less wear-resistant than Co-Cr-Mo alloy; their friction coefficients were almost identical.