Constitutive Modelling and Hot Workability Analysis by Microstructure Examination of GH4169 Alloy

Abstract

The relationships between hot deformation parameters and flow behaviour have attracted many researchers' attention for the past few decades, whilst precise constitutive modelling of GH4169 remained a problem, which seriously affected the process and microstructure control of alloys. In this work, a modified Arrhenius type model was introduced to describe the flow stresses of various compression conditions. The model showed high precision in flow stress prediction. In order to facilitate workability evaluation for engineering applications, the hot processing maps were established at the strain of 0.4~0.6. The processing maps revealed an instability domain at 900~950 • C and 0.1~1 s −1 , a high dissipation efficiency domain at 1060~1100 • C and 0.001~0.01 s −1 , and a stable deformation domain for the rest of processing parameters. Microstructures of each domain were observed via optical microscope (OM) and electron backscattered diffraction (EBSD). The intriguing finding was that the microstructures morphology agreed well with the descriptions in "discontinuous mechanism", and incompletely recrystallized microstructures were found in the instability domain. Fully recrystallized microstructures were found in the stable deformation domain, and grain coarsen in the high dissipation efficiency domain. Optimal hot working conditions were suggested based on the microstructure analysis. This investigation contributed to a comprehensive understanding of the workability of GH4169.

Hot Workability of 300M Steel Investigated by In Situ and Ex Situ Compression Tests

“…In practical production of 300M steel forgings the optimal hot working parameters could be implemented by the deformation temperature selection, punch speed selection, and pre-forging shape designing. The optimal dissipation coefficient was between 35% and 40% according to previous research [26]. When the deformation temperature and the pre-forging shape was restrained, the punch speed curves could be continuously adjusted to ensure that the average dissipation coefficient was between 35% and 40%, and under such circumstances, the finite element simulation was beneficial for the optimization of punch speed curves.…”

An Accurate Method for Crystallographic Reconstruction of Parent Austenite from Inherited Martensite in a Low-Alloy Steel

“…Furthermore, more Σ3 twin boundaries were generated at a high strain rate. This is because the formation of Σ3 twin boundaries was promoted by DRX [23,24].…”

Flow Behavior and Hot Processing Map of GH4698 for Isothermal Compression Process

“…However, the Johnson-Cook model was inadequate for materials with nonexponential type stress-strain curves, and the Zerilli-Armstrong model was established for an NiTi alloy by Shamsolhodaei et al [3]. To achieve a higher prediction accuracy, the Arrhenius model was modified to incorporate the influence of strain, and based on the modified Arrhenius model, flow stress models were established for various nickel-based alloys, e.g., the GH4169 alloy by Chen et al [4], N08028 alloy by Wang et al [5], and 80A alloy by Gu et al [6]. The results by Lin et al [7] and Wang et al [8] indicated that the accuracy of the flow stress models could be further improved by a neural network, but the applications were limited, owing to the difficulty in finite elemental integration.…”

“…Moreover, physical-based models were proposed to investigate the underlying mechanisms of the influences of creep, dislocation motion, and grain size on flow stresses by Lin et al [9], Haan et al [10], and Zhou et al [11]. By comparing the above-mentioned models, the Arrhenius model showed an advantage in applicability and accuracy, and thus it has been widely used in the flow stress modeling of nickel-based alloys [4][5][6].…”

“…By comparing the different instability criterions from Gegel et al [17][18][19][20], the different shapes of the deformation instability domains of GH79 alloy were compared by Ge et al [21], and it was noted that the deformation instability domains from Prasad's criterion could effectively predict the deformation instability of GH79. It was shown by the result of Chen et al [4] that the optimal hot working parameters of GH4169 were located at areas whose dissipative efficiencies were 30-35%. Specifically, for the GH4698 alloy, the flow behaviors were investigated by Zhang et al [22], and a flow stress model was established.…”