XU Yunbo
,
YU Yongmei
,
LIU Xianghua
,
WANG Guodong
钢铁研究学报(英文版)
Based on thermodynamics and kinetics, a new mathematical model was developed to calculate the CCT diagrams and the transformation kinetics in low carbon niobium steels, in which the effect of deformation on the degree of supercooling was taken into account. The undercooling caused by deformation is the major reason for the increase of the starting transition temperature during continuous cooling. The critical cooling rate of bainite formation is within 2-5 ℃/s for the studied niobium steels and deformation is suitable for the occurrence of pearlite. The ferrite volume fraction increases with the increase of the austenite boundary area, and decreases with the increase of the cooling rate. The calculated CCT diagrams and the volume fraction of each phase are in good agreement with the measurements.
关键词:
low carbon niobium steel;thermodynamics;supercooling degree;continuous cooling transformation;computer model
XU Yunbo
,
YU Yongmei
,
LIU Xianghua
,
WANG Guodong
钢铁研究学报(英文版)
The recrystallization kinetics and grain size models were developed for the CMn and niobiumcontaining steels to describe the metallurgical phenomenon such as softening, grain growth, and strain accumulation. Based on the recrystallization kinetics equations, the mean flow stress and the rolling load of each pass were predicted and the optimum rolling schedule was proposed for hot strip rolling. The austenite grain refinement is associated with the addition of niobium, the decrease of starting temperature of finish rolling, and the reduction of finished thickness. The mean flow stress curve with a continuous rising characteristic can be usually observed in the finish rolling of niobiumcontaining steel, which is formed as a result of the heavy incomplete softening and strain accumulation. The predicted rolling loads are in good agreement with the measured ones.
关键词:
hot strip rolling;recrystallization;mean flow stress;strain accumulation;grain size
