The Microstructure And Mechanical Properties Uniformity Control Of Direct Rolling Process For Bar And Rod

In recent years,China's industry has been unprecedented rapid development,at the same time,resource consumption and environmental pollution and other problems are also increasing.In this context,the Direct Rolling Process for Bar and Rod came into being.This process realizes the maximum use of the temperature of the continuous casting billet by the rapid blanking,the heat preservation during the transportation process,the compact connection of the front and rear processes and the reasonable scheduling of the blanking and billet feeding process,eliminating the heating step in the production process of the rod and wire,saving a considerable part.Cost and energy consumption.This process can maximize the use of continuous casting slab temperature,eliminate heating steps in rod and wire production process,and save a considerable part of cost and energy consumption through rapid billet delivery,heat preservation in the delivery process,compact connection before and after processes,and reasonable scheduling of billet delivery and billet delivery process.However,there are still some problems that need to be improved at present,such as the temperature difference between the head and tail of the casting billet caused by the continuous casting process,and the performance difference between the head and tail of the rolled piece.This paper relying on the national key project of "13th Five-Year Plan"--Key Technology of Intelligent Preparation of Long Profile(2017YFB0304200),taking a good domestic wire rod rolling technology directly intelligent production line reconstruction project as the background,combined with the trend of the domestic industrial production intelligent,combined with the temperature field model and organization performance prediction tool,the process of direct rolling process for bar and rod narrow window interval analysis,for the straight rolling process of bar wire end performance uniformity control provides theory basis.The main contents of this paper are as follows:(1)The finite difference method was used to establish the heat transfer differential model,and C language and Visual Studio 2017 platform were used to simulate the temperature field of continuous casting billet in the whole process of continuous castingtransportation-rolling-cooling production under the direct rolling process for bar and rod process.(2)The HRB400E rebar with diameter of 20mm produced by billet with 165mm× 165mm size was studied by single pass compression experiment.The dynamic softening behavior of HRB400E rebar was investigated under high temperature.The dynamic recrystallization activation energy was determined to be 324.27kJ/mol.(3)Combined with the temperature field change of the rod and wire under the DROF process,the recrystallization behavior model,phase transformation model and microstructure performance model were used to predict the microstructure and mechanical properties of the hot rolled rod.The microstructure evolution of HRB400E rebar during hot rolling and cooling was analyzed.The results showed that due to the defect of induction heating system,there was a temperature difference between the head and the tail,the ferrite grain size of the tail of the product was 0.4 microns smaller than that of the head,the yield strength of the tail of the product was 5?10MPa higher than that of the head,and the elongation rate was 0.2%lower.(4)Based on the prediction of the microstructure of the product under the direct rolling process of bar and wire,the influence of the typical control strategy of the straight rolling process on the mechanical properties of the head and tail is analyzed:Strategy 1,Change the cutting method of the casting blank from flame cutting to hydraulic cutting;Strategy 2,increase the casting speed of the continuous casting machine from 2.55m/min to 3.00m/min;Strategy 3,change the cutting method and increase the pulling speed while adjusting the induction heating system.The research shows that:strategy 1 can increase the temperature of the casting head and tail opening and rolling by 17?,and the head and tail yield strength of the product is reduced by 13MPa and 10MPa,respectively.The warming effect of Strategy 2 is more obvious,which can increase the temperature of the open and end of the billet by about 40?,and the yield strength of the product is reduced by 29MPa and 25MPa respectively.The higher temperature makes the performance difference increase.In Strategy 3,the slab heating is used to reduce the heat demand.When the induction heat compensation rate is reduced to 50%of the original heat compensation rate,the performance fluctuation of the straight rolling product is effectively improved,and the head-to-tail yield strength is reduced by 21MPa and 28MPa,the energy consumption of induction heating is reduced,and the advantages of direct rolling process for bar and rod process can be exerted.