Numerical Simulation, Microstructure, properties of EH40 ultra-heavy plate under gradient temperature rolling

This paper investigates the novel gradient temperature rolling process for ultra-heavy plates. Between rolling passes, water cooling is used to create a temperature gradient along the thickness direction of the ultra-heavy plate, which increases deformation of the core and improves the final mechanical properties of the plate. The DEFORM-3D software package was used to simulate the temperature and strain fields of the gradient temperature rolled plate. Simulation results show an obvious temperature gradient along the thickness direction of the plate and during rolling, deformation is more likely to penetrate the core. The surface to core strain ratio decreased from 14.7:1 to 1.8:1 compared to conventional rolling. Furthermore, the results of hot rolling experiments clearly show refinement of the microstructure. A layer of fine grains with an average diameter of about 1–2 μm formed on the surface of the plate and the average grain size was found to be 6.7% finer at 1/4-thickness and 11.8% finer at 1/2-thickness compared to conventionally rolled sheets. Moreover, the high-angle grain boundaries were 8.7% larger at 1/2-thickness. The microstructure of the gradient temperature rolled plate is mainly ferrite and pearlite with a small amount of granular bainite at the core. The pearlite phase initially exhibits a lamellar structure that is eventually transformed into degraded pearlite. The granular bainite is finer and more uniformly distributed compared to that of a conventional rolling plate. In addition, the yield strength and tensile strength of the gradient temperature rolling plate are higher and less elongation is observed, and the impact energy at low temperatures (−20 °C and −40 °C) is higher; from the surface to the core as the thickness increases, the decrease in impact energy is even smaller.