OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 6 No. 4 2024 Fig. 2. Change in the modulus of elasticity of low-alloy structural steels depending on the test temperature Results and discussion In order to use data shown in Fig. 2 in further calculations of contact stresses in deformation zones, the linear approximation of the elasticity modulus (Young’s modulus) ЕS dependence on temperature was performed for hot rolling of strips and equation (2) was obtained with the determination coeffi cient R2 = 0.9869 and the calculated value of the Fisher criterion (F-test). The F-test value is greater than that from the table, so the linear regression equation given below is signifi cant and gives an accurate and reliable prediction. 2.1778 0.0011 , S i E t = − ⋅ (2) where ti is the temperature of the rolled strip in the i-th mill stand, °С. The actual process mode for rolling a strip from 0.1 C-Cr-Si-Ni-Cu steel with the thickness of 2.1 mm and the width of 1,270 mm in the fi nishing seven-stand train of Mill 2000 of PAO Severstal in stands No.7, No.9 and No.11 respectively, more utilized during hot rolling, was used to study the distribution of normal contact stresses after a strip contact with working rolls. The above-mentioned features of hot rolling of low-alloyed structural steels and calculation formulas from Table 1 were used to study stresses. The target chemical composition of the specifi ed steel grade, its rolling process mode, structural parameters of deformation zones and calculated values of normal contact stresses in the above-mentioned stands are provided in Table 2. The Fig. 3 schematically represents the distribution of maximum normal stresses on the plastic section in stands No.7, No.9 and No.11 during strip hot rolling according to the mode specifi ed in Table 2. This plastic section completely consists of the stick area [11–13]. The estimated values from Table 2 and Table 3 demonstrate that maximum values of contact stresses pxmax infl uence the plastic section of the deformation zone in the lag section with the length of х2 (Fig. 1) near the neutral section, also one can see slight decrease of such stresses to maximum values р4maх on the border of the plastic and second elastic section. Taking into account the above, when determining the stress-strain state of the strip in the contact with working rolls, particularly when calculating х4 and р4maх, it is necessary to take into account the peculiarity of the change in the modulus of elasticity of the steel in Fig. 2. Calculation using formula (1), taking into account the tests of the ultimate strength of high chromium cast iron working rolls σu = 700–800 MPa [17] used in fi nishing train stands of Mill 2000, indicates that permissible contact stresses are in the range of [σ] = 1,050–1,200 MPa. Comparing the maximum normal contact stresses рхmax from Table 2 and the above permissible stresses [σ] we can conclude that these stresses are the most dangerous for the working rolls in stand No.11, because the stresses fall in the range of
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