Improvement of Tensile Properties of Commercial Eutectoid Steel by Tailoring the Microstructure and Crystallographic Data Through Quenching and Partitioning Processing

The aim of the current paper was to introduce a new heat treatment regarding the quenching and partitioning (Q&P) processing of tailoring desirable complex microstructure to obtain a good strength-ductility combination. Change in length under heating and cooling of commercial eutectoid steel was study using dilatometry to understand the kinetic of phase transformations. Then, the specimens were subjected to different Q&P paths to develop various microstructures consisting of martensite, bainite, carbide, and even retained austenite. Resulted microstructures were analyzed by x-ray diffraction, scanning electron microscopy, and electron backscattered diffraction techniques. Finally, tensile test was performed to demonstrate the role of microstructure and crystallographic data on mechanical properties. A complex microstructure containing finely dispersion of nanoscale carbide particle within the ferritic-bainite sheaves in a low tetragonal tempered martensite showed the optimum microstructure with yield strength of 950±15 MPa, ultimate tensile strength of 1710±15 MPa, and total elongation over 9.7%. Results also revealed that lattice distortion and dislocation density in the martensitic and bainitic structure are strongly dependent on carbon-partitioning from saturated martensite to untransformed austenite, austenite decomposition to bainite, formation of the transition carbides, and theirs transformation into cementite