Research On Microstructure And Properties And Process Development Of V Micro-alloy Steel Under Ultra-Fast Cooling

Good performance of impact toughness, horizontal cold bending and sinking-resistance are all needed in the use of automobile beam steel. Besides, it was required for high dimension accuracy and good shape. The microalloyelement Vanadium in the steel strengthens the matrix and the production cost is low. Applied with UFC process, the precipitation of microalloy element Vanadium in ferrite was promoted to strengthen the steel greatly and refined the grains which guides the production process of cost-saving. Vanadium microalloyed steel is getting more and more application in the production of automobile beam steel. The match of strength and ductility was optimized by the precipitation strength of V(C,N) and grain refinement of ferrite. It realized the goal of security and energy saving and has broad application prospect. The main work and obtained achievements are:(1) The material P510L (from PanGang Steel) was selected as the research object. The effect rules of deformation temperature, deformation degree and deformation rate on the resistance of deformation of this material is researched with single-pass pressing experiments. The mathematical models of the dynamic crystallization deformation and resistance of deformation were built. The static recrystallization behavior of austenite in the holding time after deformation was researched and the plot the static softening curve was drawed by using double-pass press experiments.(2) The continuous cooling phase transformation of austenite was studied with the object:V micro-alloyed steel with N-0.0160%. Fs is 730℃～622℃, Ps is 713℃～602℃and Bs is583℃～458℃.(3) With the helf of the formula of solide solution product and the kinetics equations of V(C,N) precipitation, the dissolution equation and the precipitation kinetics of four different vanadium microalloyed steels, which contains N-0.0055%,0.0107%,0.0160%,0.0193% respectively had been established with V-0.08%. The temperatures, at which the precipitation is fastest, had been achieved for different N contents.(4) Based on the grain refining and precipitation strengthening of ferrite by the precipitation of V(C,N) in ferrite, the reasonable TMCP process with rolling at recrystallization zone and UFC technology was built and the corresponding laboratory hot rolled experiments were carried out. The hot rolled process to obtain the optical mechanical properties and microstructure for four different N-contents V-microalloyed steels are developed. The accurity of the kinetics model of V(C,N) precipitation was tested by comparing the experiment results with the calculation results.