Coupled Model for Carbon Partitioning from Martensite into Austenite During the Quenching Process in Fe-C Steels
- PDF / 2,445,333 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 26 Downloads / 152 Views
TION
IN order to reduce the chemical potential difference of carbon on both sides of the ‘martensite/austenite interface’ (a¢/c interface) during the quenching and carbon partitioning (Q&P) process, carbon will diffuse from martensite (a¢) into austenite (c),[1–3] which will increase the carbon content in the austenite to improve its stability of the austenite even at room temperature (RT). The effect of this retained austenite is to provide the TRIP (transformation-induced plasticity) effect,[4] which significantly improves the elongation. There are two main Q&P processes: (a) the martensitic transformation and carbon partitioning process are independent, i.e., the carbon is permitted to partition when the martensitic transformation stops and the carbon partitioning temperature (PT) is constant or continuously rises (as shown in Figures 1(a)); and (b)) the martensitic transformation and carbon partitioning proceed simultaneously, i.e., there is still martensitic transformation during the carbon partitioning process when the carbon partitioning temperature is equal to the quenching temperature (QT), and will reduce continuously (as shown in Figure 1(b)). Many studies have focused on the carbon partitioning process without martensitic transformation (as shown in Figure 1(a)). J. Speer has constructed a thermodynamic model for carbon partitioning, the ‘Constrained Carbon Paraequilibrium model,’[2,3] which successfully explained the relationship between retained austenite content and quenching temperature without martensitic PEIXING LIU, Doctoral Candidate, BIN ZHU, Lecturer, YILIN WANG, Associate Professor, and YISHENG ZHANG, Professor, are with the State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan, 430074, China. Contact e-mail: [email protected] Manuscript submitted September 20, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
transformation. Santofimia et al. constructed a carbon partitioning model[7,8] with consideration to the movement of the ‘a¢/c interface,’ in order to explore the effects of the migration of the ‘a¢/c interface’ on the carbon partitioning process. The results show that this model can also be used to explain the phenomenon that carbon enriches from martensite into austenite. Clarke et al. found that the partitioning time has a major effect on the volume fraction of the final retained austenite, after studying the effects of partitioning time on the carbon partitioning process.[9] However, the preconditions for the above carbon partitioning process are as follows: the martensite stops transforming, and no consideration is given to the effect of martensitic transformation on the carbon partitioning process or the effect of carbon partitioning on the martensitic transformation process itself. The study of carbon diffusion velocity during the martensitic transformation conducted by Hsu et al.[10] showed that the diffusion velocity of carbon atoms keeps pace with the formation velocity of lath martensite, in which the carbon cont
Data Loading...
