Experimental study on the martensitic transformation in AISI 304 steel sheets subjected to tension under wide ranges of strain rate at room temperature

Abstract

In this work, the martensitic transformation occurring in AISI 304 steel sheets subjected to tension at room temperature has been experimentally studied. Tensile tests performed on AISI 304 specimens are split into two different types; in situ tensile tests and macroscopic tensile tests. The former are conducted mounting the sample in a tensile micromachine originally developed in ENSAM/Metz within the range of strain rates 10-5 s-1≤̇≤10-3 s-1. The latter are performed under static and dynamic conditions of deformation within the range of strain rates 10-3 s-1≤̇≤102 s-1. Using X-rays diffraction technique, in situ tensile tests have allowed measuring the stress of the phases during loading by placing the tensile micromachine under the range of a PROTO goniometer. Additionally, the martensitic transformation has been recorded via mounting the tensile micromachine into a scanning electron microscope. The volume fraction of martensite has been measured in the post mortem specimens, Vα′≈70%. Moreover, the static macroscopic tensile tests, 10-3 s-1≤̇≤10-1 s-1, have been recorded using a high speed infrared camera. It has been proven that martensitic transformation takes place in AISI 304 steel for a temperature increase over ΔT>140K. The macroscopic dynamic tensile tests are performed within the range of strain rates, 1 s-1≤̇≤100 s-1. A considerable amount of martensite has been detected in the post mortem samples, Vα′≈35%. This proves that plastic deformation is the dominant mechanism responsible for the transformation phenomenon in this steel. The free energy supplied by straining the sample relegates to a secondary role the rise in temperature taking place during the course of plastic deformation.