Experimental and numerical investigation of residual stresses around cold extrusion hole of ultrahigh strength steel

In this work, the residual stresses around the cold extrusion hole surface of ultrahigh strength steel specimen and the effects of key processing and design parameters have been systematically studied. The residual stresses at different orientations and the micro-hardness profile was established. A two-dimensional finite element (FE) model was established to simulate the residual stresses associated with the hole extrusion process and the numerical result showed a good agreement with the experimental data. The validated FE model was used to establish the effects of key processing and design parameters (including extrusion intensity, hole diameter and e/d, e is defined as the distance from the hole center to the specimen boundary and d is defined as the diameter of hole) on the residual stresses around the hole surface. The results show that, with increasing extrusion intensity, hole diameter and e/d, the maximum radial compressive residual stresses around the hole increase. With extrusion intensity larger than 6600 MPa, the hole diameter larger than 6 mm and e/d larger than 14/6, respectively, the increase in the residual stress became insignificant. With increasing extrusion intensity, the maximum tangential residual tensile stresses around the hole increases, while, the hole diameter and e/d showed no significant influence on the residual tangential stresses.