Disipace energie a nestabilita procesu při tváření středně uhlíkové oceli za tepla

Abstract

Metallic materials that have exceeded elastic deformation deform plastically with hardening. The method of determining properties is operated by means of stress-strain curves. Plastometric tests on Gleeble were used, which always allow one of the three thermomechanical mechanical parameters to remain constant. The aims of the thesis are two: namely to describe mathematically the course of these stress-strain curves and then to derive the values of energy dissipation and plastic deformation instability. This dataset was acquired via series of uniaxial hot compression tests in the temperature range of 1173 K - 1553 K and the strain rate range of 0.1 s−1 - 100 s−1. The analysis used sinh relation for determination of activation energy and other constants, which was based on experimentally measured values of peak, i.e. maximum stress, with comparison of measured and calculated values. Subsequently, process maps are compiled using the energy dissipation efficiency η and the plastic deforma-tion instability criterion ξ, and these two parameters are also interpreted together as the criteria of formability at high temperatures.