The Effect Of Grain Size On Mechanical Properties And Formability In Vanadium-alloyed Steel

Grain refining causes not only an increase of strength of metal materials but also an improvement of toughness. Ultra-fine grained steels are promising in the future. The ultra-fine grained steels no longer follow traditional mechanical properties relations, by reason of new deformation mechanism of experimental. Its formability is also different from coarse-grained material. It is necessary to study mechanical behaviors of ultrafine-grained steels in-depth.Low-carbon vanadium-alloyed steels was systematically studied to investigate the effect of deforming processing on microscopic structure and microhardness by single, multi-pass thermal test. Ultrafine-grained steels by hot continuous rolling process were tested to research the effect of different grain sizes on mechanical properties and formability. The characteristics of mechanical properties on ultrafine-grained steels were studied. It was discovered that strengthening mechanism of ultrafine-grained steels between grain sizes on mechanical properties and formability by SEM , TEM and graphic analysis method.The results are as follows: The ultra-fine grain ferrite steels microstructure and properties relation matches Hall-Patch relationship, but there is big deviation. The deviation is the slope of the Hall-Petch decrease obviously while the intercept of the Hall Petch increase markedly. The exact analyzing discovered that ultra-fine grain ferrite steel’s boundaries is thinning as grain refining, the effect of grain boundaries on mechanical property present in two aspects: With increasing the grain boundaries total length, the yield strength increase; On the other hand, the yield strength is reducing as grain boundaries thinning. Ultra-fine grain steels plate is of excellent formability, by reason of fixing the free carbide, greatly decreasing the volume percent of pearlitic structrure, obtained the single phase ferritic microstructure.