Controlling Roll Temperature by Fluid-Solid Coupled Heat Transfer

Currently, when magnesium alloy sheet is rolled, the method of controlling roll temperature is simple and inaccurate. Furthermore, roll temperature has a large influence on the quality of magnesium alloy sheet; therefore, a new model using circular fluid flow control roll temperature has been designed. A fluid heat transfer structure was designed, the heat transfer process model of the fluid heating roll was simplified, and the finite di erence method was used to cal?culate the heat transfer process. Fluent software was used to simulate the fluid?solid coupling heat transfer, and both the trend and regularity of the temperature field in the heat transfer process were identified. The results show that the heating e ciency was much higher than traditional heating methods(when the fluid heat of the roll and tempera?ture distribution of the roll surface was more uniform). Moreover, there was a bigger temperature di erence between the input and the output, and after using reverse flow the temperature di erence decreased. The axial and circum?ferential temperature distributions along the sheet were uniform. Both theoretical calculation results and numerical simulation results of the heat transfer between fluid and roll were compared. The error was 1.8%–12.3%, showing that the theoretical model can both forecast and regulate the temperature of the roll(for magnesium alloy sheets) in the rolling process.

Influence of slip ratio on worn-surface microstructure and fatigue wear behavior of D2 wheel steel

To investigate the worn-surface microstructure and fatigue cracks in D2 wheel steel under the pure rolling and 0.5% slip ratio conditions,a rolling wear test using a GPM-40 wear machine to simulate the wheel/rail operation was performed. After testing,a transmission electron microscope,a scanning electron microscope with electron backscatter diffraction,and micro-hardness testers were used to characterize the microstructure and fatigue cracks.The surface microstrncture and hardness of the pure rolling sample were in a steady state after 8 × 10^4 cycles;however,the 0.5% slip ratio sample reached a steady state after 7 × 10^3 cycles.Regardless of whether the test uses the slip ratio,the orientation of lamellar pearlites gradually became parallel to the surface and a portion of lamellar cementites was fragmented and dissolved during the formation of steady-state microstructure.The slip ratio accelerates this process.The hardening mechanism of the samples shows a decrease in the lamellar spacing of pearlite and the refinement of proeutectoid ferrite (PF).As the number of cycles increased,plastic deformation of samples became increasingly severe and the wear mechanism of the samples was fatigue wear in steady state.The sample surfaces formed shallow cracks,which gradually peeled off.The slip ratio accelerated the initiation and propagation of fatigue cracks because of the high friction stress on the contact surface.Most fatigue cracks initiated at the interface of pearlite and PF and in the PF region.

Characterization of hot deformation behavior of wear-resistant steel BTWl using processing maps and constitutive equations

In order to predict flow instability of wear-resistant steel BTW1, the hot compressions of wear-resistant steel BTW1 were firstly performed at the temperature of 900-1150 ℃ and at the strain rate of 0.05-15 s-1. Then, the constitutive relation was established based on Arrhenius-type hyperbolic sine equation. The results demonstrated that the flow stress depended on the deformation temperature and strain rate. When the deformation temperature kept constant, the flow stress increased as the strain rate increased. When the strain rate remained constant, the flow stress decreased as the temperature increased. The flow stresses calculated by constitutive equations were in a good agreement with experimental results. The apparent activation energy for deformation in the above processing region was estimated to be 369 kJ tool-1. A processing map could be obtained by the superimposition of an instability map on a power dissipation map. Based on the analysis of processing map and the microstructures, the theological instability regimes of strain rate and temperature for hot deformation of wear-resistant steel BTWl had been identified.