Effect of vanadium on the high-cycle fatigue fracture properties of medium-carbon microalloyed steel for fracture splitting connecting rod

The present investigation effort was made to study the effect of V up to 0.45% on the high-cycle fatigue properties of medium-carbon microalloyed (MA) steel 37MnSiVS, for the development of new crackable MA forging steel with excellent fatigue properties. The results show that the amount of V(C,N) precipitates increases with increasing V content and most of the precipitates are less than 5 nm. Owing to the significant precipitation strengthening effect of these nanosized particles, the hardness increase of ferrite with increasing V content is higher than that of pearlite and accordingly a decrease of pearlite/ferrite hardness ratio. Therefore, both fatigue strength and fatigue strength ratio increase with increasing V content and excellent fatigue properties could be obtained when V content is higher than about 0.28%. The fatigue crack growth (FCG) behavior is similar for all the three 37MnSiVS samples with an exponent m ≈ 3.5. It is concluded that V can improve the fatigue properties of ferrite-pearlite steel mainly through precipitation strengthening and therefore it is anticipated that MA steel's fatigue property could be further improved as well as more fine V(C,N) particles be obtained.