Evolution of structure and mechanical properties at high temperature tempering of medium carbon microalloyed steel

Abstract

The evolution of the structure and mechanical properties of medium-carbon microalloyed steel after quenching and tempering at 650оС of various durations has been studied. It is shown that the change in the microstructure and softening of steel with an increase in the duration from 2 to 3000 minutes falls on two stages of martensite tempering: medium (stage II) and high-temperature (stage III). Intensive drop of strength properties ~ 100 MPa/min at stage II is replaced by a very inert softening ~ 0.1 MPa/min at stage III. Using TEM, EBSD and X-ray diffraction analysis the evolution of the microstructure was observed and a quantitative estimation of the strengthening components and their relative contribution to the yield strength at different stages of tempering was performed.