Simulation And Experimental Study On Deformation Law Of Asynchronous Hot Rolling

As an important part of structural materials,steel materials play an important role in the process of modernization.However,with the development of science technology and industrialization,people have put forward higher requirements on the strength of materials,and at the same time,it has become a trend to increase the strength of materials under low-cost conditions.In order to avoid the decline of plastic and toughness caused by the increase of strength,this paper intends to adopt the asynchronous hot rolling process.Asynchronous hot rolling can be combined with severe plastic deformation(SPD)and thermo-mechanical control process(TMCP)for grain refinement.Asynchronous hot rolling can cause severe plastic deformation of austenite compared with synchronous hot rolling,more recrystallized nucleation sites are generated in the recrystallization temperature region,the austenite grains are fine,the austenite crystal defects after work hardening are increased in the non-recrystallization region,and the phase transformation and recrystallization nucleation point are increased.Finally,the purpose of refining the grains can be achieved in the subsequent controlled cooling process.In this experiment,the simulation and experimental research on the asynchronous hot rolling process were carried out mainly by means of simulation and pilot test.The experimental materials used low-carbon pressure vessel steel Q345R,the finite element simulation software used DEFORM-2D,and the experimental rolling mill is the Φ400 all-speed asynchronous hot rolling experimental rolling mill of the State Key Laboratory of Rolling and Automation(RAL)of Northeastern University.With the aid of optical microscope(OM),tensile testing machine,impact testing machine,EBSD,micro hardness tester,etc.The micro structure and mechanical properties of the different reduction ratios,the same velocity ratio per pass and the different velocity ratios per pass were studied.The main conclusions are as follows:(1)Under the same reduction ratio,with the increase of the velocity ratio,the equivalent strain increases along the thickness direction in the rolling cross shear zone,and the shear stress increases.When the velocity ratio is 1.2,the equivalent stress of the rolled part decreases,at the same time we can observe,as the velocity ratio increases,the macroscopic shear strain increases;(2)Taking the velocity ratio equal to 1.2 as an example,the comparison of the reduction ratios of 15%,30%and 50%can be seen that the slabs with a thickness of 20mm are rolled to 5mm after multiple passes,with each pass the reduction rate increase,the equivalent strain of the upper and lower surfaces on the outlet side increases.When the reduction ratio is 30%,the equivalent strain of the core decreases slightly.When the reduction ratio reaches 50%,the equivalent strain of the core increases;(3)Taking the reduction rate of 15%as an example,the comparison of the velocity ratios of 1.0,1.1 and 1.2 shows that the equivalent strain of the core increases with the increase of the velocity ratio;Under the rolling reduction rates of 15%,30%and 50%,the grain size of the asynchronous rolling along the thickness direction is smaller than that of synchronous rolling;At the same time,when the reduction rate is 15%,it is better to refine the grains by using 1.2 and 0.8 for interval pass speed ratio,and the grain size is less than 1.2 for each pass;(4)Asynchronous rolling charpy energy is greater than synchronous rolling,indicating that asynchronous rolling can improve the impact toughness of materials,while asynchronous rolling and synchronous rolling are all ductile fractures at room temperature,when the reduction rate is 50%and the speed ratio is 1.2,the charpy energy is the largest;(5)The tensile strength of the longitudinal rolling of the asynchronous rolling is greater than that of the synchronous rolling.When the reduction rate is 50%and the specific speed ratio is 1.2,the tensile strength of the material is the largest;Asynchronous rolling micro hardness distribution is larger than synchronous rolling in the thickness direction.When the rolling ratio is 50%,the velocity ratio is 1.2,the hardness value is the largest,and its value is 161HV.