A study for the Constitutive Equations of 1.4021 and 1.4841 Stainless Steels in Hot Deformation

Analysis of deformation processes depends on many factors such as initial shape of material and dies, rate of deformation, temperature, constitutive equation, friction and so on. In this study, constitutive equations were developed for 1.4021 and 1.4841 stainless steels and the best one was selected. Compression test was used to depict the flow stress behavior of material vs. strain. These tests were done by Dilatometer. Accuracy of results depends on the specimen geometry and lubricants in Dilatometery test. Upper bound method was used to estimate the coefficient of friction between dies and work piece. Homogenous compression is accomplished by eliminating friction at the contact surfaces or changing the initial shape of the work piece. Under homogenous compression conditions, height reduction and resulting radial and circumferential expansion are uniform throughout the test specimen. Furthermore, under these conditions, radial and circumferential stresses are zero, and the only stress acting is the uniform compressive stress in the axial direction. In this study work piece has a cylindrical shape with 5 mm diameter and 7.5 mm height and two ends were tapered with an angle 22°. Other initial shapes of work piece can be used are cylindrical, cylindrical with 16° conic angle and cylindrical with Rastegaev model. Several constitutive equations were used to describe the flow stress curves. The validity of selected constitutive equations was verified by comparing the free boundary of material after Dilatometery test and numerical simulation of the compression test using Msc.Super forge software.