Effect of tempering temperature on resistance to deformation behavior for low carbon bainitic YP960 steels

A low carbon bainitic steel YP960 for construction machinery was designed by directly quenching and tempering (DQ&T), and the mechanism for tempering temperature on tensile behavior was studied. A modified Voce relation was established using the experimental results to describe the stress-strain relationship of the as-quenched and as-tempered specimens, and quantitative model parameters for flow curve have been derived and discussed taking account into the evolution of precipitations and dislocation cell during temper. The reliability of the model was verified by a comparison between the predicted flow stress curves from the model and the experimental data. When tempering temperature is 823 K, the “hard regions” and “soft regions” form as a result of inhomogeneous recovery. With the help of Crussard-Jaoul (C-J) analysis, the cooperative deformation relationship between softer regions and harder regions was studied, which was confirmed by EBSD and TEM analysis. The cooperative deformation between softer regions and harder regions can reduce stress concentration and improve the uniform elongation of low carbon bainitic YP960 steels.