Correlation of ferrite and martensite micromechanical behavior with mechanical properties of ultrafine grained dual phase steels

Thermomechanical treatment was employed to produce ultrafine grained dual-phase (UFG DP) steels consisting of different volume fractions of martensite and different ferrite grain sizes. The effects of intercritical annealing temperature on the microstructure and deformation behavior of DP steels were investigated. The modified Crussard-Jaoul analysis illustrated four-stage deformation of the investigated DP steels. The ferrite nanoindentation response in the microstructures showed that increasing the intercritical annealing temperature from 780 to 820 degrees C, resulted in an increase in the ferrite nanohardness by about 46% due to a decrease in the average ferrite grain size by about 34%. The average martensite nanohardness decreased by about 18% with decreasing its carbon content by about 18%. The mechanical properties of UFG DP steels, such as strength, elongation, energy absorption, and strain hardening characteristics were well correlated with the ferrite and martensite micromechanical behavior.