Research and development of rational hot rolling modes of bimetallic sheets X65+316L in Ural Steel`s rolling mill 2800

The paper summarizes the experience of developing a rational mode of hot package rolling of bimetal X65+316L and its application in the conditions of existing production at the 2800 rolling mill of Ural Steel. The technology of assembling bimetallic packages (blanks) for subsequent rolling is described. The concept of thermomechanical rolling of pipe steel grades is considered and the technological modes of production of monometal of strength class X65, which serves as the main layer in the bimetal, are analysed. The main features of the production of clad plates from a package blank at the 2800 mill of Ural Steel are disclosed. The pass-by-pass distribution of therolling force and relative reduction is shown during experimental rolling of clad plates of the X65+316L combination with a thickness of 20–26 mm (cladding layer thickness 3±0.5 mm), a width of 2500–2600 mm. A rational technological mode for rolling clad plates X65+316L, developed for the conditions of the 2800 rolling mill, is presented, including: heating and holding the package at T = 1230÷1250 °C, rolling with reductions εrough ≤ 11 % and εclean = 10÷11 %, at Ter ≤ 850 °C, as well as intensive cooling of the rolled product in the CCF from the side of the main layer after rolling, which made it possible to master the production of clad plates with a thickness of 20–26 mm for pipe purposes (combination of X65 + 316L) from bimetallic packages. The article presents the results of studies and tests of bimetallic plates rolled using rational hot rolling modes, which confirmed the achievement of the specified rolled product quality parameters: tensile strength of bimetallic plates ranged from 550 to 600 MPa (strength classes K55 (X60) – K56 (X65), shear stress 482 – 536 MPa, impact toughness KCV 280-310 J/cm2 at 0 °C, not less than 250 J/cm2 at -20 °C and not less than 200 J/cm2 at -40 °C, the proportion of the viscous component after Drop-Weight Tear Test (DWTT) 90-100% at –20 °C, 100 % continuity at ultrasonic testing according to GOST 22727 class 1, absence of delamination by multidirectional bending at an angle of not less than 120°.