An effect of static recrystallization with inclusion interaction and a change of tensile mechanical properties of drawn free cutting steels 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 ware performed on two types of cold-drawn free-cutting steels 11SMnPb30 and a lead-free 11SMnBi30 as a non-toxic variant of the first one. The rough square-shaped bars were delivered in high strength state (Re = 716 MPa, Rm = 765 MPa) and low plasticity (A4 = 9%) and final fixing products.
A series of electron backscattered diffraction (EBSD) mapping of selected area was used for monitoring of static recrystallization process on in-situ heated sample from 450 up to 550 °C to provide information about structural changes. The original heavily-deformed structure with many dislocation sub-cells started the recovery process at 450°C and continued to a massive recrystallization at 550°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 connected with TESCAN SEM image acquisition.