OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 6 4 4 permissible values [σ] in several estimated points of the deformation zone рхmax and pnmax (Fig. 3). The fact of the maximum loading of the roll system of the four-high stand No.11 according to the existing production technology in the fi nishing train of the Mill 2000 is also confi rmed by studies in [18]. The risk of further growth of maximum contact stresses рхmax increases signifi cantly during hot rolling of strip sections with higher longitudinal thickness variation due to fl uctuations in the force Рi as a function of all crucial process factors [19, 20], therefore the risks of surface damage, reduced lifetime, or destruction of working rolls and the risk of emergency roll change increase due to repetitive loading and heavy thermal stresses [21–23]. It should also be noted that rolling of low-alloyed structural steels in the conditions of real production of the fi nishing train is performed before scheduled rolls change in all stands of Mill 2000, therefore the calculated values of maximum contact stresses рхmax and pnmax (Fig. 3) really aff ect the working roll lifetime. The studies [19, 20] can be used as a potential for improving the technology of hot-rolled high-strength steel strips production in the fi nishing train of a wide-strip mill to ensure high durability of working rolls. The essence of the proposed improvement in rolling strips of high-strength steels is that the increase of percentage reductions εi in the fi rst three stands of the Mill 2000 fi nishing train in the rolling direction to maximum permissible values of reductions εi.max or Pi.max force, as specifi ed in the mill technical passport data, have no signifi cant impact on growth of maximum normal contact stresses рхmax because of high Ta b l e 2 Chemical composition of 0.1 C-Cr-Si-Ni-Cu steel, rolling process condition and the results of calculating the structural parameters of the deformation zone and normal contact stresses Chemical composition, % С Si Mn Cr Mo Ni Al Cu Nb Ti V 0.102 0.87 0.55 0.63 0.05 0.53 0.016 0.46 0.001 0.003 0.002 Rolling stand No. 7 9 11 Outgoing thickness hi, mm 10.43 3.99 2.33 Percentage reduction εi, % 48.16 34.27 19.09 Back tension σi−1, MPa 20 30 40 Front tension σi, MPa 30 30 40 Rolling speed υi, m/s 2.3 5.76 10.36 Strip temperature ti, oС 1,024 984 939 Coeffi cient of friction μi 0.418 0.295 0.24 Plastic resistance σpl, MPa 167 239.9 315.1 Young’s modulus for work rolls ЕR, MPa 205,000 185,000 185,000 Young’s modulus for a strip ЕS, MPa 105,165 109,497 114,494 Rolling force Рi, MN 33.46 23.13 19.97 Length of deformation zone lc, mm 63.8 29.56 26.76 Elastic section length x4, mm 4.85 6.31 8.18 Maximum normal contact stresses р1max, MPa 172.6 247.1 327.7 Maximum normal contact stresses on the plastic section рхmax, MPa 332.5 645.9 1,067.7 Normal contact stresses in the neutral section рnmax, MPa 328.5 643.3 1,066.9 Maximum normal contact stresses р4max, MPa 190.5 378.9 798.3
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