DETERMINATION OF HARDENING CURVES OF HSLA STEEL IN THE PROCESS OF COLD ROLLING

Based on the methods and principles of the mathematical theory of experiment, in mechanical properties (yield strength, ultimate strength) the changes are investigated of hardly-deformed steel for the automotive industry (grades HC260LA, HC300LA, HC380LA, HC420LA to EN10268). It concerns the process of cold deformation. In industrial production of cold-rolled sheet a single-factor experiment was planned and carried out. To eliminate the influence on the result of independent factors (heterogeneity of chemical composition, mode of hot-rolled, of cold deformation) experimental randomization was performed. Samples of hot-rolled steel are selected for each brand from the strips of different heats. Three samples across the width of the strip were cut on sections of length with steady state regime of rolling. Cold rolling with a fixed level degree of deformation was performed on the laboratory mill for each group of samples with different combination of independent factors. Tensile test was performed under identical conditions for all samples with different sets of independent factors and degree of deformations. A statistical appraisal of the results of the experiment was executed. Obtained values of the yield strength and the ultimate strength for each test steel were smoothed by a three-parameter dependence of A. V. Tretyakov, using the method of least squares. An algorithm for approximating the results of the experiment is implemented as a program. Hardening curves of HSLA steel were built in cold deformation process. Results of the experiment are used in a mathematical model "Cold Rolling" for calculating and optimization modes of cold-rolling of HSLA steel on the mill 2030.