Stress current of metal is one of the main parameters that have a significant impact on the calculation accuracy of energy and force parameters of rolling. A great contribution to the creation of the metal flow stress calculation methods is made by: Zyuzin V., Brovman M., Dinnik A., Andreyuk A., Nikolaev V., etc. In this work we propose an improved method of calculating the metal flow stress at the base of the planned experiment. Experiments are designed as the plan of the second order. Researches are conducted for the following steel grades: normal quality construction steel 3; construction quality carbon non-alloyed steel 45; ball bearing steel ШХ 15, construction alloyed steel 12XН3A; high-alloyed stainless steel XH18H9T. It is applied orthogonal central compositional planning based on three factors: ε (the grade of deformation), υ (the speed of deformation), Θ (deformation temperature). The relationship between the real and coded variables was determined by the formula.
хi = (Χi - xi0)/δi,(1.1)where хi - code value of the; Χi - natural value of variable; xi0 - value of i-th variable at zero-level; δi - changing interval of the i-th variable. The results of the translation of natural variables into the code ones are presented in Table 1. Table 1 - Encoding factors and their levels of variation
It is proposed to determine current stress of the metal in the form of a polynomial of second degree
σ = a0 + a1ε + a2υ + a3Θ + a4ευ + a5εΘ + a6υΘ + a7ευΘ + a8ε2 + a9υ2 + a10Θ2, (1.2)where a0,a1,...,a10 - polynomial coefficients based on the results of experimental information on σт. Because of technological considerations, the following boundaries for study of factors were chosen: ε = 0,2 - 0,4, υ = 10 - 100с-1, Θ = 900 - 12000С. Calculation to determine the metal stress current were held by the methods: Zyuzin V., Andreyuka L., Nikolaev V. and the new formula. Pattern matrix of experiment, the results of calculations by the method of V. Zyuzin and the new formula for steel 12ХН3А presented in Table 2.
Table 2 - Plan matrix of experiment, the results of calculations by the method of V. Zyuzin and the new formula for steel 12ХН3А
The coefficients of the polynomial (1.2) are defined using the program Statistica, and are presented in Table 3.
Table 3 - The coefficients of the polynomial (1.2)
As a result of the calculations it was determined that the average error of the flow stress of metal by the method of V. Zyuzin in relation to the experimental data is 3.9%. Similar calculations obtained by other methods. Under the new method error was 1.0%.