The effect of thermomechanical treatment on the microstructure and mechanical properties of AISI ۴۳۴۰ steel

In order to evaluate Ferrite-Bainite microstructure on mechanical properties of AISI ۴۳۴۰ steel, new thermo mechanical treatment (TMT) were done. TMT including austenitizing, apply reduction in cross-sectional area (rolling), quenching in water and then intercritical annealing, austempering and finally quenching in cold water. Ferrite-Bainite microstructure with different volume levels of ferrite and bainite were produced. The microstructures were characterized by X-ray diffraction, and scanning electron microscopes (SEM). The “Image J” software was used to determine the volume fraction of the ferrite. Hardness and tensile tests were performed according to standard on produced samples. The produced samples with new TMT showed a significant increment of tensile strength while the elongation did not change much compared to the prototype. Tensile strength was reached from ۱۰۶۰ to ۱۶۴۰ MPa with ۲۰% elongation. Since on an industrial scale the issue of energy saving is important. The presented new method reached to the high strength in a short cycle time with respect to conventional methods.

Keywords:

AISI ۴۳۴۰ steel , thermo mechanical treatment (TMT) , Ferrite-Bainite , mechanical properties , intercritical annealing , microstructure