Abstract
Iron–nickel based ultra-high strength steel (wt. 18~20% Ni) is characterized by its high strength and low thermal conductivity, and is normally used to make key components by forming and machining processes. The optimization of these processes is based on a deep understanding of the mechanical and dynamic behaviors under high strain, high strain rate, and high temperature. In this paper, the relationship of stress to strain, strain rate, and temperature is systematically investigated by the dynamic compression tests combined with quasi-static compression tests, and the hardening and softening is associated with the transformation in microstructures. According to the analysis, dynamic recrystallization around 600 °C is assumed to be one important influencing factor, hence hot deformation equations are established and the critical strain for dynamic recrystallization and the volume fraction of the dynamic recrystallized grains are defined.
Highlights
Iron–nickel based ultra-high strength steel is a kind of low carbon Fe-Ni martensite steel with inter-metallic compound precipitated and hardened by aging treatment
It is found that continuous dynamic recrystallization (CDRX) in the thermal is formed by breaking the matrix grains, generating low angle grain boundaries by a large number deformation is not achieved by nucleation and growth of new grains like static recrystallization, but of dislocations, gradually converting to high angle grain boundaries and forming the recrystallized is formed by breaking the matrix grains, generating low angle grain boundaries by a large number grains [28,29,30,31,32,33]
The of deformation stress to strain,are strain rate, and temperature systematically investigated by the dynamic compression relationship of stress to strain, strain rate, andand temperature is systematically investigated tests combined with quasi-static compression tests, the underlying mechanisms are discovered.by the dynamic compression combinedbased withultra-high quasi-static compression and underlying
Summary
Iron–nickel based ultra-high strength steel (wt. 18~20% Ni) is a kind of low carbon Fe-Ni martensite steel with inter-metallic compound precipitated and hardened by aging treatment. 18~20% Ni) is a kind of low carbon Fe-Ni martensite steel with inter-metallic compound precipitated and hardened by aging treatment It is used in a wide variety of applications in transportation industries owing to its unique comprehensive mechanical properties, i.e., ultra-high strength up to 2.2 GPa, good plasticity and toughness, high hardness, excellent fatigue resistance and low crack propagation rate [1,2,3,4]. The SHPB technique has been used to determine the dynamic behaviors of iron–nickel based ultra-high strength steel under the impact compressive loading conditions of strain-rates ranging from 103 s−1 to 104 s−1 and temperatures from 25 ◦ C to 1200 ◦ C, and the microstructures of the samples after compression are observed and analyzed. Two shims with much higher strength are added at both ends of the sample
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