Deformation and Fracture Testing for Hot Working Processes

Abstract

A hot workability testing apparatus has been designed and constructed for determining flow stress and fracture of materials at elevated temperatures. The system is composed of four major elements: a closed-loop servo-controlled hydraulic testing machine with programmable and custom-made control components; a high temperature tooling and radiant heating furnace for isothermal test conditions; a test specimen transfer device for ease of testing and rapid quenching; and a computerized data acquisition and reduction system. Isothermal, homogeneous compression tests are performed for flow stress determination, while upset and bend tests are used for workability evaluation. Test temperatures to 1200°C may be achieved, along with constant strain rates up to 20s’1 for both compression and bend tests. Specimens can be quenched within 0.5-0.75s to permit the study of the microstructures developed during hot deformation. In both compression and bending, interrupted deformation schedules can be programmed. Change of rate tests to measure strain rate sensitivites are also possible. Capabilities of the system are illustrated by results obtained for the multiphase alloy MP35N (35% Co, 35% Ni, 20%o Cr, and 10% Mo).