STUDY OF THE EFFECT OF CARBON PARTITIONING ON THE MECHANICAL AND ELECTROCHEMICAL PROPERTIES OF THE SAE 9254 STEEL
In the present work, of effect of a quenching and partitioning cycle on the mechanical and electrochemical properties of the SAE 9254 steel was studied. Initially, the critical phase transformation temperatures were assessed by dilatometry. The samples were treated following four quenching and partitioning routes using quenching interruption temperatures of 200 °C and 250 °C and reheating temperatures of 300 °C and 400 °C. Quantitative assessment of the ferrite and austenite phases was undertaken by X-ray diffractometry. Qualitative analysis was carried out by optical microscopy (OM) and scanning electron microscopy (FEG-SEM) coupled to EDS detector for evaluating the presence of segregations. Mechanical properties were evaluated by Vickers microhardness and nanoindentation tests. Electrochemical properties were assessed by electrochemical impedance spectroscopy and potentiodynamic polarization using a 0.1 M NaCl solution as the electrolyte. X-ray diffraction revealed the presence of retained austenite for the samples subject to all treatment routes with similar contents. Microstructural characterization by OM showed the presence of martensite and retained austenite, with segregation regions. EDS analysis of these regions revealed the presence of manganese, silicon, chromium and carbon. Dilatometric curves showed volumetric expansion during the reheating step, evidencing secondary martensite formation (fresh martensite).