In this study,the three-windows method,the jump-ratio method and the R-map method in energy-filtered transmission electron microscopy(EFTEM) have been applied to mapping carbon distribution in 35SiMn steel after a quenching-partitioning treatment.The carbon contamination is successfully suppressed by using EFTEM and plasma-cleaning TEM samples.Compared to the three-windows method and the jump-ratio method,the R-map method provides carbon distribution with less noises,and is insensitive to changes in sample thickness.We have demonstrated that the R-map method is a better way for carbon mapping in middle-carbon steel without the influence of carbon contamination.
The cementite formation and coarsening behaviors of 0. 2 mass% C-5 mass% Mn steel during tempering at 500℃ were investigated by in-situ transmission electron microscope（ TEM）. In-situ TEM observation showed uniform distribution of cementite particles at the early stage of tempering in the rapidly heated（ 500 ℃ / s） sample. Elemental analysis confirmed that the cementite growth was dominated by Mn diffusion. During the cementite growth,the coarsening behavior of intragranular cementite was significantly controlled by the matrix diffusion,while that of the intergranular cementite was mainly governed by the boundary diffusion. The in-situ TEM observation revealed that the dislocation pipe diffusion of Mn took place during tempering,which accelerated the Mn diffusion between cementite particles. The coarsening rates of individual cementite particles were calculated based on the in-situ TEM observation.
Ye XIAXi-nan LUOXiao-yan ZHONGHui-hua ZHOUCun-yu WANGJie SHI
Mn distribution and austenite morphology at the early stage of intercritical annealing of 5Mn steel were investigated. It was experimentally demonstrated that a newly formed 20 nm-thick austenite was formed without the partitioning of Mn. The elemental analysis confirmed that the growth of austenite should be controlled by the diffusion of C prior to the diffusion of Mn at a low heating rate. The austenite growth started under negligible-partitioning local equilibrium mode and then switched to partitioning local equilibrium mode. Mn segregation at the γ/α interface suggested that the collector plate mechanism was the essential way of Mn partitioning at the early stage of austenite growth.
Xi-nan LUOXiao-yan ZHONGHai-wen LUOHui-hua ZHOUCun-yu WANGJie SHI
