Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Microstructure Evolution and Fracture Mechanism of 55NiCrMoV7 Hot- Working Die Steel during High Temperature Tensile

Version 1 : Received: 15 May 2023 / Approved: 18 May 2023 / Online: 18 May 2023 (11:21:28 CEST)

A peer-reviewed article of this Preprint also exists.

Yuan, Y.; Wang, W.; Shi, R.; Zhang, Y.; Xie, J. Microstructure Evolution and Fracture Mechanism of 55NiCrMoV7 Hot-Working Die Steel during High-Temperature Tensile. Metals 2023, 13, 1056. Yuan, Y.; Wang, W.; Shi, R.; Zhang, Y.; Xie, J. Microstructure Evolution and Fracture Mechanism of 55NiCrMoV7 Hot-Working Die Steel during High-Temperature Tensile. Metals 2023, 13, 1056.

Abstract

In this paper, through high-temperature tensile tests of 55NiCrMoV7 steel, the high-temperature fracture behavior, microstructure evolution and carbide distribution characteristics of both thermal-mechanical coupling zone (fracture zone) and thermal stress zone (clamping zone) at different temperatures were studied. Intrinsic relationship between high temperature fracture and carbides types, distribution and size were revealed and evolution mechanism of microstructure near cracks in 55NiCrMoV7 hot-working die steel during high temperature deformation was clarified. Samples were stretched at different temperatures from 25 °C to 700 °C, and microscopic examinations were carried out by using SEM and TEM. The results showed that: With the increase of temperature, tensile strength and yield strength decreased, elongation and reduction of area increased, and fracture mode changed from brittle fracture to ductile fracture by transition temperature at about 400℃. During high temperature deformation, the grain dislocation density decreased, the tempered martensite decomposed, recovered, recrystallized, and then grain grew. M7C3 and M23C6 carbides precipitated and grew along the grain boundary, and a small amount of fine granular MC carbides were dispersed in the grain. The work done by the external force on the deformation zone would cause the temperature of it to be higher than tensile temperature, which provides thermodynamic conditions for the re-dissolution of small carbides near the fracture zone and the grain growth of large carbides, resulting in the decrease of small carbides and increase of large carbides in thermal-mechanical coupling zone.

Keywords

55iCrMoV7 steel; hot- working die steel; microstructure evolution; high temperature fracture mechanism; carbides

Subject

Chemistry and Materials Science, Materials Science and Technology

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