Transactions of Materials and Heat Treatment

Title：Research on hot deformation behavior and processing map for 40Mn steel

Authors： Kong Delei Lei Liping Zeng Pan

Unit： Tsinghua University

KeyWords： 40Mn steel dynamic recrystallization high-temperature rheological stress model processing map microstructure

ClassificationCode：TG142.1+4

year,vol(issue):pagenumber：2019,44(3):122-132

Abstract：

The isothermal compression test was carried out by Gleeble-1500D thermo-mechanical simulator to study the hot deformation behavior and dynamic recrystallization of 40Mn steel. Then, the high-temperature rheological stress model and the processing map were established, and the microstructure of compressed specimens was observed by the Optical Microscope. The results show that the high temperature rheological stress of 40Mn steel can be described by a hyperbolic sine model including dynamic recrystallization characteristic, and the average deformation activation energy of thermal deformation is 300.48 kJ·mol-1. Therefore, 40Mn steel has the characteristic of dynamic recrystallization softening, and there are obvious differences in the processing map under different strains. Furthermore, the processing map is divided into work hardening-dynamic recovery stage and dynamic recrystallization stage. In the work hardening-dynamic recovery stage, there are two processing instability regions located at 900 ℃-1 s-1 and 1200 ℃-1 s-1 respectively, and the mechanisms are adiabatic shear zone and grain boundary cracking respectively. In the dynamic recrystallization stage, there is a processing instability zone located in the low-temperature and high-strain-rate zone, and the mechanism is adiabatic shear zone. There is an optimal processing zone with temperature 1050-1150 ℃ and strain rate 0.003-0.01 s-1, which is a dynamic recrystallization zone. The ‘necklace’ microstructure at 850 ℃-1 s-1 is observed, which verifies the reliability of the processing map and provides the guidance for the evaluation of hot workability and research the forging process.

Funds：

国家重点研发计划(2017YFB0701800)

孔得磊(1993－)，男，硕士研究生，E-mail： kdl16@mails.tsinghua.edu.cn；通讯作者: 雷丽萍(1968－)，女，博士，副研究员，E-mail: leilp@mail.tsinghua.edu.cn

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