Research On Cold Rolling Strip Behavior Based On The Variation Of Material's Mechanical Properties

The cold rolling strip has been widely used in industrial fields such as automobile, construction due to its low energy consumption, low cost, high production efficiency and good plate shape quality. The mechanical properties of the strip would be changed during the rolling processes, which will directly affect the plate shape and the distribution of stress-strain in the strip. Such complicated stress-strain distributions make it much harder to predict the behavior of cold rolling strip. At present, the study on the changing of material's mechanical properties during rolling process is still lack of systematic analysis.The strip is subjected to a series of external forces such as tension, rolling force, friction, etc. And the strip subjects to a large plastic deformation during rolling process. Because of the work hardening phenomenon, the stress state in the strip rolling zone would become more complicated. In this paper, to measure the variation of mechanical properties after each rolling step, a series of experiments were performed. First, five rolled plate samples were obtained through the continuous rolling tests with different cold rolling steps. The in-situ tensile tests were taken to get the tensile-elongation relationship. Then the weighted average method and finite element method were adopted to obtain the true stress-strain relationships included necking process. To obtain the mechanical properties and microstructures of each rolling step, the SEM, metallographic microscope and microhardness tests were conducted. The material properties after rolling step were introduced into the finite element software ABAQUS to analyze the stress-strain behavior of the strip during continuous rolling process.The results showed that the elastic modulus, yield strength and the tensile strength of the strip increase obviously with the addition of rolling step, while the ductility of the strip decreases distinctly. The grain of the strip steel material is elongated along the rolling direction. And the degree of lattice distortion gradually increases after each rolling process. The microhardness of the material also increases along the rolling process. Compared with the simulation results of constant material properties and the varied material properties the error of stress in rolling zone and residual stress became bigger with the rolling step increased. While the difference between the strain and the thickness along the rolling direction is neglectable. In the simulation of plate with edge notch, it is found that the notch shape changed consistent with the rolling experiment through varied material properties. The stress and strain distribution of the leading edge of the defect can be analyzed accurately with varied properties.