Numerical and Experimental Investigations on Residual Stress and Hardness within a Cold Forward Extruded Preform

Abstract

Using a preform fabricated by a cold forward extrusion process, the present study numerically predicted and experimentally investigated its residual stress and microstructural characteristics, as well as its plastic deformation damage and hardness. Prior to realizing the preform, AISI 1035 cold-drawn medium carbon steel material with a diameter of 50.0 mm and a height of 121.0 mm is first spheroidized and annealed, after which phosphophyllite is used to coat its outer surface. To identify the influence of the spheroidizing and annealing on the mechanical properties and the microstructural phase, uniaxial compression tests and microscopic observations are carried out. After assuming the deformation behavior of the workpiece during the cold forward extrusion with a plastic material model and with an elasto-plastic material model, separately, three-dimensional finite element simulations are adopted to visualize the residual stress and the plastic deformation damage. The preform produced by cold forward extrusion is fully scanned by using an optical 3D scanner, the Vickers micro-hardness is measured, and the residual stress through EBSD (electron backscatter diffraction) analysis is observed. Briefly, the results show that the ferrite and pearlite within the raw workpiece is well spheroidized by the heat treatment, and that there is a decrease in the KAM (kernel average misorientation) value of about 40%. In terms of the preform obtained by the cold forward extrusion, the dimensional requirement is more suitably met with the predicted layout when adopting the elasto-plastic material model than that of the plastic material one, and the numerically predicted residual stress agrees with the Vickers micro-hardness distribution. It can be verified that the dislocation density (or the internally stored strain energy) based on the IQ map and the IPF map is substantially increased around the extrusion region, and that the KAM value is increased by roughly 516% as the whole average of the observed values.

Simulation Study on Temperature and Stress Fields in Mg-Gd-Y-Zn-Zr Alloy during CMT Additive Manufacturing Process

“…Additionally, the residual stresses at the center of the weld beads for each layer were measured using X-ray diffraction and compared with simulated data. Figure 12 uses the Kernel Average Misorientation (KAM) diagram to represent the average orientation difference between two adjacent points [ 39 , 40 , 41 ]. The KAM diagram shows that the residual stress of the 1st layer is the largest, and the residual stress of the 11th layer is greater than that of the 6th layer.…”

Simultaneous Enhancement of Strength and Sulfide Stress Cracking Resistance of Hot-Rolled Pressure Vessel Steel Q345 via a Quenching and Tempering Treatment

“…Another important factor for triggering SSC failure is residual stress [33][34][35], which is closely related to the plastic deformation accompanied by phase transformation. A Kernel average misorientation (KAM) map of the EBSD that reveals local misorientation and the strain energy may be used to estimate the stress distribution [36][37][38]. Figure 5 shows a typical KAM map, in which the green area indicates the strain induced by a high dislocation density.…”

Ejector pin-related high-cycle fatigue fracture of the critical die corner during automatic multistage cold forging of an automotive wheel nut

“…The ejector pin may apply counterpressure to prevent the material's fracture during forward extrusion [ [11] , [12] , [13] ]. In the stepped long shaft forging, the ejector pin usually plays no considerable role during the plastic deformation of the material [ [14] , [15] , [16] ], even though it can exert some counterpressure on the bottom side of the material [ 13 ]. On the contrary, the material during manufacturing the short or flat forgings may exert a significant force on the ejector pin, which may be considered a die part.…”

“…Hu et al [ 15 ] predicted the ejector pin's force during ejecting the material after the forward and backward extrusion process with an emphasis on the lubrication. Ku [ 16 ] numerically and experimentally studied the evolution of residual stress, damage, and hardness during the cold forward extrusion, considering the effect of the ejecting process on them.…”