Bimetallic rolls are widely used in steel rolling industries because of the excellent hardness, wear resistance, and high-temperature properties. The control of the residual stress distribution is necessary since the compressive residual stress at the surface may improve fatigue life although the central tensile residual stress may cause fracture originating at the center. Recently, to reduce the tensile stress appearing at the roll center, quenching heat treatment is performed just after heating the roll nonuniformly instead of uniformly with sufficient time. In this paper, the quenching processes after uniform and nonuniform heating are compared on the basis of FEM simulation. It should be noted that a large amount of experimental data of the core and shell materials is utilized for the wide range of temperature including the quenching process. The results show that the tensile stresses at the roll center for nonuniform heating are less than that for uniform heating by 89MPa (26%) at the maximum stress point, although the same compressive stresses appear at the surface. The inner layer tensile residual stress increased by 14% with increasing diameter from 600mm to 800mm in uniform heating, but tensile residual stress was almost unchanged in nonuniform heating.
When scaling down a conventional forming process to the microscale, the influence of the size effect must to be considered. This effect comes from the material properties and frictional behavior at the microscale. We investigate the effect of grain size on the forward-backward micro-extrusion behavior of an aluminum alloy using a desktop experimental setup. The extrusion force increases with decreasing grain size, which agrees with the Hall-Petch effect. The backward extrusion length increases with decreasing grain size because of the tendency of small grains to flow into the small backward extrusion gap. A micro-Vickers hardness test shows that a smaller billet grain size leads to more significant work hardening upon plastic deformation. We focus on the simulation of micro-extrusion for a 6063 aluminum alloy billet by the ALE-based finite-element method. In this process, the material is extruded both forward and backward with dependences on the grain size and friction conditions. The metal flow separation caused by an increasing friction coefficient indicates that the friction at the die-billet interface affects the complicated metal flow in forward-backward extrusion.