Deformation Behavior And Fatigue Properties Of Carbon Non - Quenched And Tempered Steel With Different Vanadium Content

Vanadium is the most main microalloyed elements in microalloyed steel; Its content is usually controlled below0.15%. As the scope of application expand and more demanding of service condition, demands for its comprehensive performance is getting higher and higher, particularly fatigue performance. To this paper, by using Gleeble3800testing machine, rotating-bending fatigue test, SEM, OM and other test means, exploring high temperature hot deformation behavior, controlled forging cold behavior and high cycle fatigue behavior in the two different content of V (V1,0.15%; V2,0.28%) of microalloyed steel.First, in this paper, the continuous cooling transformation curves of the tested steels were research by Gleeble-3800thermal simulation testing machine, the law of the phase were investigated, Combined with the actual forging parts features of controlled cooling after forging process has carried on the laboratory simulation. The results show that with the increase of vanadium content, the critical cooling rate of ferrite+pearlite microstructure transformation decreases, the CCT curves of test steels moved to the right obviously. With the increase of deformation, the ferrite volume fraction increases. When forging deformation, the deformation induced transformation to promote the precipitation of ferrite phase, thus compared with high temperature heating without deformation (heat treatment), the strength of the test steel in forging state level reduced.Single compression tests were carried out using Gleeble-3800thermal simulator to investigate the hot deformation behavior of two vanadium microalloyed medium-carbon steels for fracture splitting connecting rod. The results show that the hot deformation behavior of the tested steels is similar to that of conventional medium-carbon microalloyed steels and dynamic recrystallization is easier to occur at higher deformation temperature and lower strain rate. The austenite deformation resistance and activation energy of deformation increases with increasing vanadium content and thus the starting time of dynamic recrystallization was delayed. Finer recrystallization austenite grain size could be obtained at higher strain rate and lower deformation temperature and vanadium content has little effect on recrystallization austenite grain size. TEM observation reveals that vanadium is mainly in dissolved condition in austenite and thus affects the dynamic recrystallization behavior of the tested steels.The high-cycle fatigue properties of the experiment steels were studied by using rotating-bending fatigue test. The results show that both fatigue limit and the ratio of fatigue limit to tensile strength of37MnSiVS steel are significantly higher than those of38MnVS steel and quenched and tempered40Cr steel, which are562MPa,0.614, respectively. With the increase of V, higher quantity of finely distributed V (C, N) particles were formed, and these V (C, N) particles have specific orientation relationship with ferrite matrix and thus significant effect on precipitation strengthening and microstructure refinement. The finer and uniform microstructure and lower microhardness ratio of pearlite to ferrite of37MnSiVS steel are the main reasons for37MnSiVS steel has even better high-cycle fatigue properties.