Characterization of Isothermally Heat-Treated High Carbon Nanobainitic Steels

Isothermal heat treatment close to the martensite-start temperature at various transformation times, followed by hardness and compression tests, has been performed for three new high carbon experimental nanobainitic steels. Microstructural characterization clearly revealed the formation of lower bainitic structures with plate thickness in the range of nanometers. Analysis of the volume fraction of the bainitic phase via x-ray diffraction indicates that the presence of Co and Al accelerates the transformation resulting in almost complete transformation within 24 h. The effect of transformation and the resulting microstructure on the mechanical properties are also presented. Finally, the data collected from the compression tests have been used to develop an enhanced correlation between the yield strength and hardness in steels. Comparison of the improved correlation with three other frequently used correlations from the literature reveals a good performance of the proposed correlation.