Effect of annealing time and phosphorus addition on bake hardening behavior of ultra-low carbon bake hardening steel  

作　　者：Xi-liang Zhang Hua-feng Hou Tao Liu Qian Zhou Hong-ji Liu Yu-long Zhang Hao-xuan Cui Zheng Lv 

机构地区：[1]College of Mechanical and Equipment Engineering,Hebei University of Engineering,Handan 056038,Hebei,China

出　　处：《Journal of Iron and Steel Research International》2018年第12期1287-1295,共9页

基　　金：the National Natural Science Foundation of China (Nos.51874114 and 51501052);the Youth Talent Support Program of Hebei Province (No.BJ2017056).

摘　　要：The relationship of the P and C grain boundary segregation and its effect on bake hardening behavior were investigated in ultra-low carbon bake hardening (ULC-BH)steel with and without P addition annealed at 810 ℃ for various time using electron probe micro-analyzer,electroh backscattered diffraction,and three-dimensional atomic probe techniques.Results revealed that P addition and annealing duration considerably affected the bake hardening behavior of experimental steel. The BH value of ULC-BH steel without P addition is lower than that with P addition within a short annealing time,and the difference in the BH value gradually decreases as the annealing duration is prolonged.P segregation is dominant in terms of a high P bulk content in steels with P addition at the expense of C segregation during annealing.By contrast,opposite effects are observed in low carbon bake hardening steel.The high residual solute C content in steel with P addition is due to P segregation at the grain boundary.Site competition is mainly responsible for the lower BH value in ULC-BH steel without P addition than that with P addition.As the annealing time is further extended,C segregation begins at grain boundary despite the delayed P segregation,leading to a gradual decrease in the solute concentration in the matrix of steels with P addition.C and P segregations reach the equilibrium as the annealing time increases to 60 min at 810 ℃ in the two steel samples.Theoretical calculations reveal that the residual solute C concentration in the matrix decreases to zero,and this finding is consistent with the change trend of the bake hardening value.Hence,the C segregation at grain boundary. adversely influences the bake hardening property of ULC-BH steel.

关 键 词：Ultra-low CARBON BAKE HARDENING steel CARBON PHOSPHORUS ADDITION BAKE HARDENING BEHAVIOR Grain boundary segregation 

分 类 号：TF[冶金工程]