Effect Of V On Precipitation Behavior Of Second Phase,Microstructure And Properties In Ti-Mo Microalloyed Steels

China is one of the countries with affluent reserves of titanium(Ti)resource.It has important economic and strategic meanings to develop high performance Timicroalloyed steels because of the low price of Ti ore compared with other microalloying elements,resulting in a more competitive advantage in the production costs by utilizing full potential of Ti microalloying.It is found that the addition of vanadium(V)is favorable for the precipitation hardening and combination properties of the Ti-Mo microalloyed steel.However,it has not been fully understood on the influence mechanism of V on the precipitation behavior of the procipiates and microstructure-properties of Ti-Mo microalloyed steels.In the present study,Ti-Mo and Ti-Mo-V steels were used to clarify the effects of V on the thermodynamics and kinetics of precipitation.In addition,the effects of V on the microstructure-properties of Ti-Mo microalloyed steels during continuous cooling,the coiling and the tempering processes were analyzed.Results in the present study provide reference and theoretical basis for the producing of high performance Ti-microalloyed steels.In order to clarify the effects of V on the precipitation behavior of the Ti-Mo microalloyed steels,the precipitation behavior of Ti-Mo and Ti-Mo-V steels were studied by theoretical calculation combined with experimental method.In the high temperature austenite region,V promoted the precipitation of Ti-Mo steel,while in the low temperature austenite region.V delayed the precipitation of Ti-Mo steel.The addition of V increased the precipitation nucleation rate of Ti-Mo steel in ferrite,and the precipitation start time was advanced,which promoted the precipitation of Ti-Mo steel in the ferrite region.Moreover,the coarsening rate of precipitates in Ti-Mo-V steel was slightly larger than that of Ti-Mo steel.To clarify the effects of V on the microstructure-properties of the Ti-Mo microalloyed steels during the continuous cooling process,thermal simulation experiments and related microstructural observations were conducted.Results demonstrate that V decreased the decomposition temperature of the austenite during cooling and shortened the transformation area of ferrite-pearlite,made the bainite area move towards to bottom left and inhibited bainitic transformation of undercooled austenite.The microstructure-properties of Ti-Mo and Ti-Mo-V steels were studied by means of laboratory rolling and microscopic observation,aiming at clarifying the effects of V on microstructure-properties of Ti-Mo microalloyed steels during coiling.The austenite grain size and ferrite grain size of Ti-Mo-V steel were both larger than those of Ti-Mo steel after deformation.When the coiling temperature changed between 550~650°C,the yield and tensile strengths of Ti-Mo steel decreased with the increase of coiling temperature,while they firstly increased and then decreased with the increase of coiling temperature in the Ti-Mo-V steel.Moreover,the change of elongation was not obvious in the Ti-Mo and Ti-Mo-V steels.The strength of Ti-MoV steel was higher than that of Ti-Mo steel under the same coiling temperature.In order to analyze the effect of V on the microstructure and properties in Ti-Mo microalloyed steels during tempering,the microstructure and hardness of Ti-Mo and Ti-Mo-V microalloyed steels were compared.The results indicate that the hardness of Ti-Mo-V microalloyed steel was larger than Ti-Mo microalloyed steel at the same tempering temperature and time.In addition,at the same tempering temperature,the hardness values of two experimental steels decreased and then increased followed by decreasing again with the increase of tempering time.