In-Situ Study Of Recrystallization And Deformation Processes In Free-Cutting Steel

An effect of static recrystallization with inclusion interaction and a change of tensile mechanical properties of drawn free-cutting steel has been studied in the scanning electron microscope (SEM) equipped with a combined in-situ heating and tensile stage. The main goal of all in-situ tests was to effectively improve plasticity and optimize strength which is important for application of the final products from free-cutting steels. The tests were performed on two types of cold-drawn free-cutting steels 11SMnPb30 and a lead-free variant 11SMnBi30. The rough square-shaped bars were delivered in high strength state (R-e = 607 MPa, R-m = 658 MPa) and low plasticity (A(5) = 10 %) and final fixing products. A series of electron backscattered diffraction (EBSD) mapping of selected area was used for monitoring of static recrystallization process [1-3] on in-situ heated sample from 450 up to 550 degrees C to provide information about structural changes. The original heavily-deformed structure with many dislocation sub-cells started the recovery process at 450 degrees C and continued to a massive recrystallization at 550 degrees C. The influence of inclusions on all processes were studied as well. After sample cool down to the room temperature a tensile experiment was performed to compare the change of mechanical properties of the recrystallized sample to the original state of cold-drawn sample without any thermal treatment. A novel approach of multi-site in-situ deformation process monitoring has been used utilizing an advanced software integration and automation possibilities of a combined tensile-heating stage by NewTec and with TESCAN SEM image acquisition.