Effect of Different Austempering Heat Treatments on Corrosion Properties of High Silicon Steel
Mattia Franceschi,
Luca Pezzato,
Alessio Giorgio Settimi,
Claudio Gennari,
Mirko Pigato,
Marina Polyakova,
Dmitry Konstantinov,
Katya Brunelli,
Manuele Dabalà
Affiliations
Mattia Franceschi
Department of Industrial Engineering, University of Padua, Via Marzolo 9, 35131 Padova, Italy
Luca Pezzato
Department of Industrial Engineering, University of Padua, Via Marzolo 9, 35131 Padova, Italy
Alessio Giorgio Settimi
Department of Industrial Engineering, University of Padua, Via Marzolo 9, 35131 Padova, Italy
Claudio Gennari
Department of Industrial Engineering, University of Padua, Via Marzolo 9, 35131 Padova, Italy
Mirko Pigato
Department of Industrial Engineering, University of Padua, Via Marzolo 9, 35131 Padova, Italy
Marina Polyakova
Department of Mechanical Engineering and Metallurgical Technologies, Nosov Magnitogorsk State Technical University, pr. Lenina, 38, 455000 Magnitogorsk, Russia
Dmitry Konstantinov
Department of Mechanical Engineering and Metallurgical Technologies, Nosov Magnitogorsk State Technical University, pr. Lenina, 38, 455000 Magnitogorsk, Russia
Katya Brunelli
Department of Industrial Engineering, University of Padua, Via Marzolo 9, 35131 Padova, Italy
Manuele Dabalà
Department of Industrial Engineering, University of Padua, Via Marzolo 9, 35131 Padova, Italy
A novel high silicon austempered (AHS) steel has been studied in this work. The effect of different austenitizing temperatures, in full austenitic and biphasic regime, on the final microstructure was investigated. Specimens were austenitized at 780 °C, 830 °C, 850 °C and 900 °C for 30 min and held isothermally at 350 °C for 30 min. A second heat treatment route was performed which consisted of austenitizing at 900 °C for 30 min and austempering at 300 °C, 350 °C and 400 °C for 30 min. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been used to evaluate the microstructural evolution. These techniques revealed that the microstructures were composed of carbide-free bainite, ferrite, martensite and retained austenite (RA) in different volume fractions (Vγ). An aqueous borate buffer solution with 0.3 M H3BO3 and 0.075 M Na2B4O7∂10H2O (pH = 8.4) was used for corrosion tests in order to evaluate the influence of the different volume fractions of retained austenite on the corrosion properties of the specimens. The results showed that when increasing the austenitization temperatures, the volume fractions of retained austenite reached a maximum value at 850 °C, and decrease at higher temperatures. The corrosion properties were investigated after 30 min and 24 h immersion by means of potentiodynamic polarization (after 30 min) and electrochemical impedance spectroscopy (after both 30 min and 24 h) tests. The corrosion resistance of the samples increased with increases in the volume fraction of retained austenite due to lower amounts of residual stresses.
