TY - JOUR
T1 - Characterization of bainitic/martensitic structures formed in isothermal treatments below the Ms temperature
AU - Navarro-López, A.
AU - Hidalgo Garcia, J.
AU - Sietsma, J.
AU - Santofimia Navarro, M.J.
PY - 2017
Y1 - 2017
N2 - Advanced Multiphase High Strength Steels are generally obtained by applying isothermal treatments around the martensite start temperature (Ms). Previous investigations have shown that bainitic ferrite can form from austenite in isothermal treatments below Ms, where its formation kinetics is accelerated by the presence of the athermal martensite. That athermal martensite is tempered during the isothermal treatment, and fresh martensite may form during the final cooling to room temperature. The distinction between product phases present after the application of this type of heat treatments is difficult due to morphological similarities between these transformation products. The aim of this study is to characterize the structural and morphological features of the product phases obtained in isothermal treatments below the Ms-temperature in a low-carbon high-silicon steel. Multiphase microstructures, having controlled fractions of product phases, were developed by applying isothermal treatments above and below Ms, and were further studied by electron back scatter diffraction (EBSD) and scanning electron microscopy (SEM). The bainitic or martensitic nature of these product phases is discussed based on this characterization. Results showed that bainitic ferrite appears in the form of acicular units and irregularly shaped laths. Tempered martensite appears as laths with a sharp tip and as relatively large elongated laths with wavy boundaries containing protrusions.
AB - Advanced Multiphase High Strength Steels are generally obtained by applying isothermal treatments around the martensite start temperature (Ms). Previous investigations have shown that bainitic ferrite can form from austenite in isothermal treatments below Ms, where its formation kinetics is accelerated by the presence of the athermal martensite. That athermal martensite is tempered during the isothermal treatment, and fresh martensite may form during the final cooling to room temperature. The distinction between product phases present after the application of this type of heat treatments is difficult due to morphological similarities between these transformation products. The aim of this study is to characterize the structural and morphological features of the product phases obtained in isothermal treatments below the Ms-temperature in a low-carbon high-silicon steel. Multiphase microstructures, having controlled fractions of product phases, were developed by applying isothermal treatments above and below Ms, and were further studied by electron back scatter diffraction (EBSD) and scanning electron microscopy (SEM). The bainitic or martensitic nature of these product phases is discussed based on this characterization. Results showed that bainitic ferrite appears in the form of acicular units and irregularly shaped laths. Tempered martensite appears as laths with a sharp tip and as relatively large elongated laths with wavy boundaries containing protrusions.
KW - Austenite decomposition
KW - Bainitic ferrite
KW - Dilatometry
KW - EBSD characterization
KW - Isothermal treatments
KW - Martensite
UR - http://resolver.tudelft.nl/uuid:de810159-0656-49f0-b3bf-96d83caef022
U2 - 10.1016/j.matchar.2017.04.007
DO - 10.1016/j.matchar.2017.04.007
M3 - Article
SN - 1044-5803
VL - 128
SP - 248
EP - 256
JO - Materials Characterization
JF - Materials Characterization
ER -