Baoguang Sang

The evolution of carbides and the impact toughness of a vacuum‐melted H13 steel were studied under different spheroidizing annealing conditions. The main carbide types identified after annealing were Cr ₇ C ₃ , Cr ₂₃ C ₆ , Mo ₂ C, Mo ₆ C, and VC. Prolonging the holding time led to a gradual increase in the average carbide size, indicating that excessively long holding times should be avoided. During isothermal holding, carbide growth followed the Ostwald ripening mechanism. The impact toughness exhibited an initial increase followed by a decrease with extended isothermal time. After 2 h of isothermal treatment, the formation of chain‐like carbides along grain boundaries resulted in lower toughness. At 3 h, these chain‐like carbides gradually dissolved, yielding carbides with moderate size and a relatively uniform distribution, corresponding to an average impact energy of 22.1 J. In contrast, further extension to 4 and 5 h promoted pronounced carbide coarsening and the dissolution of numerous fine carbides, leading to a considerable deterioration in impact toughness.

1. Die-casting was used to produce large quantities of parts that require high dimensional accuracy and surface roughness, and its production efficiency is high and the cost is low. Die-casting die...

The hot deformation characteristics of M50 steel in the temperature range of 900–1150 °C and strain-rate range of 0.01–10 s⁻¹ was investigated in this study using a Gleeble-3800 thermal simulation testing machine. The true stress–strain curves showed that the deformation resistance increased with decreasing deformation temperature, and increasing strain rate before the peak stress was reached. After the peak stress, dynamic reversion occurred, and consequently, the deformation stress decreased. The softening phenomenon was more obvious when the strain rate was low. The calculated values of the thermal deformation-activation energy Q and stress index n were 233,684.2 J/mol and 5.025568, respectively. On this basis, the Arrhenius-type constitutive equation was established, and in addition, a polynomial fit based on strain was performed to obtain the 9th-order strain-compensated constitutive equation with high fitting accuracy. By processing the flow stress curves, the processing maps of M50 steel were constructed, and the optimal processing range was predicted to be in the range of 1070–1150 °C and 0.01–1 s⁻¹. The recrystallization behavior of M50 steel was also studied by constructing a dynamic recrystallization kinetic model and combining optical microscope (OM) and electron backscatter diffraction (EBSD) observation. The results show that with the increase of deformation temperature, the degree of recrystallization transformation increased accordingly, and the original grains were gradually replaced by recrystallized grains. Besides, in the optimal process zone for thermal processing, the recrystallized grains grew with decreasing strain rate and increasing temperature.