Effect of Holding Temperature on Microstructure and Mechanical Properties of High-Strength Multiphase Steel

Isothermal holding following intercritical annealing is usually used in microstructure control, e.g., fractions and stabilities of retained-austenite (RA). Fe-0.22C-2.5Mn-0.47Si-0.41Cr-0.02Nb (mass%) steel is subjected to intercritical annealing and isothermal treatment at 250, 300, 350, and 400 degrees C to elucidate the impact on microstructures and mechanical properties by means of electron microscopy and uniaxial tensile test, respectively. The results show that the isothermal holding temperature is vital for the formed phases, including the morphology, volume fraction, and carbon content of RA in the processed steels. The tensile test results indicate that the mechanical properties including Ultra-tensile strength (UTS), Yield strength (YS), as well as Total Elongation (TEL) are attributed to the synthetic action of all constituents of phase morphology and corresponding fractions, e.g., hard-to-soft phase ratio, morphology and fraction of RA, dispersed precipitates. An excellent combination of strength-ductility of the present multiphase steel has been explained in terms of their specific microstructure.