Papers by Author: L.D. Yao

Abstract: Two mild steels with Nb-microalloying and Nb-free were smelted. After single-pass hot compression of various processes conducted on a Gleeble-2000 thermomechanical simulator, the effects of deformation conditions and Nb-microalloying on microstructural evolution kinetics, including the volume fraction, grain size and grain number per unit area were investigated through quantitative metallographic analysis. The experimental results show that, grain number per unit area of DIF increases with decreasing deformation temperature or increasing deformation amount; the grain size of DIF is not very sensitive to the deformation conditions; the volume fraction of DIF increases due to the increased grain number per unit area. The microalloying element of Nb dissolved in austenite inhibits the grain growth and reduces the volume fraction of DIF.

Abstract: In this study, a TMCP was attempted to obtain a low carbon high strength Nb-Ti microalloyed dual phase with low yield ratio at Baosteel. Optical and scanning electron microscopy was utilized to analyze microstructures. A mixed fine microstructures consisting of acicular ferrite and martensite/austenite was observed. The austenite maintained a small grain size during reheating in the temperatures ranging from 1100°C to 1250°C. The growth of austenite was strongly retarded by Nb and Ti nitride and carbide. The higher end cooling temperature (650°C) had much influence on the refinement of microstructures, especially the length of ferrite packets, whereas the lower temperatures (600-500°C) had little effect on the microstructure refinement.