RESEARCH ON MATERIAL FLOW-STRESS BEHAVIOR AND THE DIE-FORGING PROCESS FOR FORGED-STEEL BRAKE DISCS FOR HIGH-SPEED TRAINS

Due to the large size and complicated features, the brake discs of high-speed trains are difficult to forge, so a reasonable design of the process and the die parameter are prerequisites for successful forming. The flow stress of 23CrNiMoV, a forged-steel brake disc material for high-speed trains, was investigated by a uniaxial compression experiment on a Gleeble 1500 test machine. Based on the obtained flow-stress data, a series of numerical simulation analyses of the die forging of high-speed-train brake discs were carried out by using finite-element software. The effects of forging temperature, flash groove parameters and forming speed on the flow filling, forming load and temperature change of metal during die forging were studied. The simulation results were optimized and better process parameters were obtained. Based on the obtained process parameters, the simulation of the forming process was completed and a better forming quality was obtained.

Interactions Between Dynamic Softening and Strengthening Mechanisms During Hot Forging of a High-Strength Steel

Open-die forging is a critical step in the manufacture of large numbers of components used in the transportation and energy industries. Dynamic recrystallization, dynamic transformation, and dynamic precipitation take place during the hot deformation process and significantly affect microstructure conditioning, which ultimately influences the service properties of the component. In the present work, using a Gleeble 3800 thermomechanical simulator, the open-die forging of a large-size ingot made of a modified AISI 6140 medium carbon high-strength steel is investigated. Deformation temperatures ranging from 950°C to 1,250°C and strain rates ranging from 0.01 to 1 s−1, representative of the actual process, are considered in the analysis. The generated true stress–true strain curves are used as a basis for the development of a constitutive model predicting the occurrence of softening and strengthening phenomena as a function of thermomechanical conditions. The corresponding activation energy is determined to be about 374 kJ mol−1 and is compared against the values reported in the literature for other high-strength steels. Dynamic recrystallization kinetics is studied using the t50 model, and the influence of temperature and strain rate is quantified and discussed. The interaction between dynamic precipitation and dynamic recrystallization is discussed, and the deformation conditions under which such interactions occur are determined. The thermomechanical results are validated by microstructure examination, including laser confocal microscopy, field emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy. The present study focuses on reproducing the deformation cycle applied during the open-die forging process of a vanadium-containing high-strength steel used in the industry with special attention to the interaction between dynamic recrystallization and precipitation processes.

Research of stamping of unequal channel bars. Part 5. Methods for calculating the extrusion of channels. 3. Calculations of the extrusion of the hardening material

Experimental studies on the extrusion of channels from a hardening material have carried out. Comparison of the results with theoretical calculations showed the high accuracy of the obtained formulas. Keywords: die forging, extrusion, misalignment, punch, matrix, plane strain. [email protected]

Research of stamping of unequal channel bars. Part 5. Methods for calculating the extrusion of channels. 2. Extrusion of non-strengthening material

The results of experimental studies on the extrusion of channels from non-strengthening material are presented. Comparison of theoretical calculations with experimental results showed the high accuracy of the derived formulas. Keywords: die forging, extrusion, punch, matrix, misalignment, plane strain. [email protected]

Research of stamping of unequal channel bars. Part 5. Methods for calculating the extrusion of channels. 1. Alculation formulas

Calculation formulas for determining the most important parameters of the channel extrusion process are given. Keywords: die forging, extrusion, misalignment of a punch and a matrix, plane strain. [email protected]